tag:theconversation.com,2011:/ca/topics/fault-lines-5922/articlesFault lines – The Conversation2023-09-22T10:50:15Ztag:theconversation.com,2011:article/2141522023-09-22T10:50:15Z2023-09-22T10:50:15ZView from The Hill: We can’t prepare for a future pandemic without fully looking at state governments’ decisions in the last one<figure><img src="https://images.theconversation.com/files/549736/original/file-20230922-26-xus58y.jpg?ixlib=rb-1.1.0&rect=10%2C5%2C3338%2C2389&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption"></span> </figcaption></figure><p>Nearly a year ago, a privately financed inquiry, led by Peter Shergold, a former head of the prime minister’s department, finished a review of Australia’s handling of the COVID pandemic.</p>
<p>The report, Fault Lines, was a solid piece of work, delving into the commendable and poor aspects of the response to what was such a massive health and economic crisis.</p>
<p>Among its findings were that lockdowns and border closures should have been used less and schools in the main should have been kept open. Both internal borders and schools were state responsibilities.</p>
<p>Australia always needed a federal government-commissioned inquiry into the management of the pandemic. Anthony Albanese recognised this and before the election he indicated Labor would have one. But he was vague about its form.</p>
<p>Now we have seen that form, and it’s clearly inadequate.</p>
<p>The terms of reference, issued on Thursday, say the inquiry will take a “whole-of-government” view. A whole of Commonwealth government, that is.</p>
<p>They are very detailed. But Albanese and Health Minister Mark Butler summed up the inquiry’s remit when they said in a statement it would consider Commonwealth responses, including “the provision of vaccinations, treatments and key medical supplies to Australians, mental health support for those impacted by COVID-19 and lockdowns, financial support for individuals and business, and assistance for Australians abroad”.</p>
<p>While looking at these areas will inevitably lead the inquiry into the various interfaces with the states, the terms of reference specifically say it will not extend to “actions taken unilaterally by state and territory governments”.</p>
<p>The inquiry will be done by a three-member panel, comprising Robyn Kruk, who has formerly headed departments at state and federal level; Catherine Bennett, an eminent epidemiologist, and Angela Jackson, a health economist.</p>
<p>There was immediate criticism that the inquiry is not a royal commission. Albanese dismissed this line of attack, suggesting royal commissions took a long time, and judges weren’t necessarily the best people for this job. These arguments sounded somewhat strange, however the fact it isn’t a royal commission is not the central problem here.</p>
<p>That problem is its failure to include the decisions of the states and territories – and notably that line emphasising their specific exclusion.</p>
<p>The COVID response was as much at state as federal level – in fact, on many aspects the states were the drivers. For example the Morrison government did not favour schools being closed, but state governments took a different view and did it.</p>
<p>So why exclude the states’ decisions? There is no logic about that, but it looked like some obvious politics was at play.</p>
<p>Facing criticism that he was protecting Labor states, Albanese pointed to the political mix of these governments at the time, when half of them were non-Labor. He also said there had been changes of government and leadership in some states.</p>
<p>One, more credible, reason for excluding state decisions is to avoid giving ammunition for a possible future change of government. The Palaszczuk government goes to an election in late October next year. That government came under much criticism over its uncompromising border closure during COVID, with damaging publicity about a lack of compassion. It is already facing an uphill fight to hang onto power. The last thing it would want would be an inquiry – which reports by September 30 next year – revisiting earlier decisions.</p>
<p>(Victoria’s Dan Andrews, who ran the harshest lockdowns, has his election behind him, but likely wouldn’t appreciate any potentially tough findings either.)</p>
<p>After what the government must have found an unexpectedly fierce attack over its inquiry, Butler on Friday argued it could get into state matters.</p>
<p>It would examine the health response – which included the public health and social measures. And they covered “distancing, contact tracing, border closures, lockdowns, all of those things are in scope. They’re utterly in scope of the inquiry. It would be extraordinary for them not to be,” he told the ABC.</p>
<p>That leaves the whole thing as clear as mud. On Butler’s words, it would seem up to the panel how far it wants to push the probing of state areas.</p>
<p>But broadly, it appears the Morrison government will have the blow torch applied, while the state administrations of the time will at most only get some indirect heat.</p>
<p>Albanese says the inquiry is aimed at looking forward to how we can be better prepared for the future.</p>
<p>But without a forensic eye on what was good and bad in the decisions taken by all governments, we will only receive partial advice on how to put Australia in the best position to deal with another such crisis. And by limiting the inquiry, the government has invited a cynical response from the public, who got to know quite a lot about how various governments performed in those hard times.</p><img src="https://counter.theconversation.com/content/214152/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michelle Grattan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Australia needed a federal government-inquiry into the management of the pandemic. Albanese recognised this and before the election he indicated Labor would have one. But he was vague about its form.Michelle Grattan, Professorial Fellow, University of CanberraLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2061722023-05-29T20:08:57Z2023-05-29T20:08:57ZEarthquakes can change the course of rivers – with devastating results. We may now be able to predict these threats<figure><img src="https://images.theconversation.com/files/528476/original/file-20230526-29-ge5jx9.jpg?ixlib=rb-1.1.0&rect=53%2C22%2C5027%2C3046&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Getty Images</span></span></figcaption></figure><p>New Zealand’s 2016 Kaikōura earthquake stopped the Waiau Toa – also known as the Clarence River – in its course. Within hours, the river flooded outside its channel and changed course. In the seven years since the magnitude 7.8 earthquake, the river has completely abandoned the path it used to take. </p>
<p>This is not the first time this sort of thing has happened.</p>
<p>Flooding and earthquakes are some of the most <a href="https://www.weforum.org/agenda/2016/01/which-natural-disasters-hit-most-frequently/">frequent natural disasters</a> globally. A great deal of work has been done to understand their risk – but relatively little to determine how they can occur at the same time. </p>
<p>This is a problem. Tens of thousands of active faults run under river channels around the world and in New Zealand. In places where faults and rivers intersect, earthquake and river flood hazards are also intertwined. </p>
<p><a href="https://www.science.org/doi/10.1126/sciadv.add2932">Our new research </a> shows that when a fault deforms the earth’s surface, it can cause an overlying river to suddenly flood outside its established channel. This can put unsuspecting communities at risk.</p>
<p>In some cases, the sudden river shifts – also known as avulsion – may even cause the river to establish a new channel within the landscape. </p>
<p>There are many examples of this phenomenon throughout history, including the 1812 <a href="https://www.britannica.com/event/New-Madrid-earthquakes-of-1811-1812">Reelfoot fault rupture</a>, which dammed the mighty Mississippi river for several hours. The same earthquake also permanently dammed the Reelfoot river, creating Reelfoot Lake.</p>
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Read more:
<a href="https://theconversation.com/nobody-can-predict-earthquakes-but-we-can-forecast-them-heres-how-199757">Nobody can predict earthquakes, but we can forecast them. Here's how</a>
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<p>Earthquakes occur due to sudden movement on faults. When a fault ruptures to the surface, it can shift one side of the fault vertically past the other. This can cause a large block of land to be permanently uplifted or depressed. </p>
<p>Where faults run under rivers, this vertical movement can produce a fault scarp – a wall of rock and/or soil – that obstructs the river’s ability to continue flowing in its usual channel. </p>
<p>This is what happened in Kaikōura in 2016. The Papatea Fault ruptured and created a 6.5 meter high barrier within the channel of the Waiau Toa, stopping the river in its course and rapidly and permanently altering the path it takes.</p>
<p>But can we predict this sort of thing before it happens?</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/527888/original/file-20230524-19-g3pkhd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/527888/original/file-20230524-19-g3pkhd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=746&fit=crop&dpr=1 600w, https://images.theconversation.com/files/527888/original/file-20230524-19-g3pkhd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=746&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/527888/original/file-20230524-19-g3pkhd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=746&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/527888/original/file-20230524-19-g3pkhd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=938&fit=crop&dpr=1 754w, https://images.theconversation.com/files/527888/original/file-20230524-19-g3pkhd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=938&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/527888/original/file-20230524-19-g3pkhd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=938&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Photographs taken the day after, and five years following, the 2016 Kaikōura earthquake, show how the landscape has changed.</span>
<span class="attribution"><span class="license">Author provided</span></span>
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</figure>
<h2>Forecasting shifts</h2>
<p>Data from the Kaikōura earthquake offered an opportunity to test whether these sorts of shifts in river flows, and potential flooding, can be “forecast” in advance. Turns out, it might be possible.</p>
<p>We constructed two flood models that aimed to reproduce the Waiau Toa river shift. The first model used topographic data obtained following the 2016 Kaikōura earthquake, containing the real Papatea fault scarp. The second model simulated the avulsion using pre-earthquake topography, modified with an artificial Papatea fault scarp. </p>
<p>Both models performed well, and accurately reproduced patterns of flooding that took place in 2016. This indicates that changes in river flood patterns following surface rupturing earthquakes can be predicted ahead of time. </p>
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Read more:
<a href="https://theconversation.com/seismologists-cant-predict-an-impending-earthquake-but-longer-term-forecasts-and-brief-warnings-after-one-starts-are-possible-199666">Seismologists can't predict an impending earthquake, but longer-term forecasts and brief warnings after one starts are possible</a>
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<p>That said, it is impossible to predict the exact amount of surface displacement a fault may produce when it ruptures, or the exact river flow conditions when it does. Instead, flood modelling can be used to explore scenarios ahead of time using historical flow information and historic fault data. </p>
<p>Applying this to the Papatea fault rupture, we found that sudden shifts in the flow of the river may not immediately happen if the river is low.</p>
<h2>Better planning</h2>
<p>This is important, as it suggests that flooding could be delayed following a surface rupturing earthquake if the affected river is running low. Yet a river may still change course later, as the flow rate increases. </p>
<p>Creating flood models ahead of time may allow planners to identify key zones along the river that are exposed to this hazard. They can then put in measures that will reduce the impact of the flooding, such as levees. </p>
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Read more:
<a href="https://theconversation.com/nzs-next-large-alpine-fault-quake-is-likely-coming-sooner-than-we-thought-study-shows-159223">NZ's next large Alpine Fault quake is likely coming sooner than we thought, study shows</a>
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<p>New Zealand’s position atop a plate boundary means earthquakes are a <a href="https://www.gns.cri.nz/our-science/natural-hazards-and-risks/earthquakes/">common natural hazard</a>. Flood hazards are also increasing in <a href="https://theconversation.com/floods-cyclones-thunderstorms-is-climate-change-to-blame-for-new-zealands-summer-of-extreme-weather-201161">frequency and severity </a>. </p>
<p>Kaikōura is not the only community that could be affected by the combination of earthquakes and flooding.</p>
<p>Many of New Zealand’s active faults underlie rivers located near populated areas, or critical infrastructure. Examples include the Wellington fault, which underlies the Hutt River, and the Titri fault and Taieri river intersection which borders Dunedin airport and several towns. </p>
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<img alt="" src="https://images.theconversation.com/files/528477/original/file-20230526-7168-4sat7f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/528477/original/file-20230526-7168-4sat7f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=329&fit=crop&dpr=1 600w, https://images.theconversation.com/files/528477/original/file-20230526-7168-4sat7f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=329&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/528477/original/file-20230526-7168-4sat7f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=329&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/528477/original/file-20230526-7168-4sat7f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=413&fit=crop&dpr=1 754w, https://images.theconversation.com/files/528477/original/file-20230526-7168-4sat7f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=413&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/528477/original/file-20230526-7168-4sat7f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=413&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Kaikōura’s landscape changed significantly after the magnitude 7.8 (Mw) earthquake in November 2016.</span>
<span class="attribution"><span class="source">Getty Images</span></span>
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<p>Yet we typically do not consider how these rivers may change following a surface rupturing earthquake, meaning nearby populations and infrastructure remain exposed and unprepared. The unique combination of earthquake and flooding is rarely considered in existing flood management strategies or earthquake response plans. </p>
<p>It is imperative that existing earthquake response plans consider the influence of active faults that underpin river systems. Current flood models that neglect their presence may underestimate the extent, longevity and patterns of flooding following earthquakes. </p>
<p>Our modelling provides a path forward. With some knowledge of fault location and rupture style, the interactions between surface rupturing earthquakes and river flood hazards can be explored ahead of time.</p><img src="https://counter.theconversation.com/content/206172/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Funding for this work is provided by the New Zealand Earthquake Commission, Ministry of Business, Innovation & Employment Endeavour Fund and GNS Science.</span></em></p>Earthquakes can cause rivers to unexpectedly change course. New research reveals we may be able to predict the resulting flooding – and plan better for future disasters.Erin McEwan, PhD candidate in Geological Sciences, University of CanterburyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1996662023-02-15T13:25:59Z2023-02-15T13:25:59ZSeismologists can’t predict an impending earthquake, but longer-term forecasts and brief warnings after one starts are possible<figure><img src="https://images.theconversation.com/files/510218/original/file-20230214-14-uyfac2.jpg?ixlib=rb-1.1.0&rect=589%2C380%2C4203%2C2356&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Seismologists monitor the Earth's activity, but they can't predict a day, time and place for the next 'big one.'</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/technicians-of-the-national-seismological-center-of-the-news-photo/829643960">Christian Miranda/AFP via Getty Images</a></span></figcaption></figure><p><em>Almost like aftershocks, questions about earthquake prediction tend to follow disasters like the one that occurred Sept. 8, 2023, in Morocco. Could advance notice have prevented some of the devastation? Unfortunately, useful predictions are still in the realm of science fiction.</em></p>
<p><em>University of Washington professor of seismology and geohazards <a href="https://scholar.google.com/citations?user=ull69vcAAAAJ&hl=en&oi=ao">Harold Tobin</a> heads the <a href="https://pnsn.org">Pacific Northwest Seismic Network</a>. He explains the differences between predicting and forecasting earthquakes, as well as early warning systems that are currently in place in some areas.</em></p>
<h2>Can scientists predict a particular earthquake?</h2>
<p>In short, no. Science has not yet found a way to make actionable earthquake predictions. A useful prediction would specify a time, a place and a magnitude – and all of these would need to be fairly specific, with enough advance notice to be worthwhile.</p>
<p>For example, if I predict that California will have an earthquake in 2023, that would certainly come true, but it’s not useful because <a href="https://temblor.net/earthquake-insights/overdue-the-future-of-large-earthquakes-in-california-12667/">California has many small earthquakes every day</a>. Or imagine I predict a magnitude 8 or greater earthquake will strike in the Pacific Northwest. That is <a href="https://www.newyorker.com/magazine/2015/07/20/the-really-big-one">almost certainly true</a> but doesn’t specify when, so it’s not helpful new information.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/510220/original/file-20230214-22-a065v2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="rectangular map of Earth with tectonic plates outlined" src="https://images.theconversation.com/files/510220/original/file-20230214-22-a065v2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/510220/original/file-20230214-22-a065v2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=342&fit=crop&dpr=1 600w, https://images.theconversation.com/files/510220/original/file-20230214-22-a065v2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=342&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/510220/original/file-20230214-22-a065v2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=342&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/510220/original/file-20230214-22-a065v2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=429&fit=crop&dpr=1 754w, https://images.theconversation.com/files/510220/original/file-20230214-22-a065v2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=429&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/510220/original/file-20230214-22-a065v2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=429&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Tectonic plates fit together like puzzle pieces made of the Earth’s crust.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/tectonic-plates-move-constantly-making-new-areas-of-royalty-free-image/1146522618">Naeblys/iStock via Getty Images Plus</a></span>
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<p>Earthquakes happen because the <a href="https://www.usgs.gov/faqs/what-earthquake-and-what-causes-them-happen">slow and steady motions of tectonic plates</a> cause stresses to build up along faults in the Earth’s crust. Faults are not really lines, but planes extending down miles into the ground. Friction due to the enormous pressure from the weight of all the overlying rock holds these cracks together.</p>
<p>An earthquake starts in some small spot on the fault where the stress overcomes the friction. The two sides slip past each other, with the rupture spreading out at <a href="https://www.usgs.gov/faqs/what-was-duration-earthquake-why-dont-you-report-duration-each-earthquake-how-does-duration">a mile or two per second</a>. The grinding of the two sides against each other on the fault plane sends out waves of motion of the rock in every direction. Like the ripples in a pond after you drop in a stone, it’s those waves that make the ground shake and cause damage. </p>
<p>Most earthquakes strike without warning because the faults are stuck – locked up and stationary despite the strain of the moving plates around them, and therefore silent until that rupture begins. Seismologists have not yet found any reliable signal to measure before that initial break.</p>
<h2>What about the likelihood of a quake in one area?</h2>
<p>On the other hand, earthquake science today has come a long way in what I’ll call forecasting as opposed to prediction.</p>
<p>Seismologists can measure the movement of the plates with <a href="https://www.iris.edu/hq/inclass/animation/measuring_plate_tectonics_with_gps">millimeter-scale precision using GPS technology</a> and other means, and detect the places where stress is building up. Scientists know about the recorded history of past earthquakes and can even infer farther back in time using the <a href="https://www.usgs.gov/programs/earthquake-hazards/introduction-paleoseismology">methods of paleoseismology</a>: the geologically preserved evidence of past quakes.</p>
<p>Putting all this information together allows us to recognize areas where conditions are ripe for a fault to break. These forecasts are expressed as the likelihood of an earthquake of a given size or greater in a region over a period of decades into the future. For example, the <a href="http://pubs.usgs.gov/of/2013/1165/">U.S. Geological Survey estimates the odds</a> of a magnitude <a href="https://www.usgs.gov/faqs/what-probability-earthquake-will-occur-los-angeles-area-san-francisco-bay-area">6.7 or greater quake in the San Francisco Bay Area</a> over the next 30 years is 72%.</p>
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<a href="https://images.theconversation.com/files/510222/original/file-20230214-30-ka8so1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="collapsing bridge and roadway with black smoke and fire engine" src="https://images.theconversation.com/files/510222/original/file-20230214-30-ka8so1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/510222/original/file-20230214-30-ka8so1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=374&fit=crop&dpr=1 600w, https://images.theconversation.com/files/510222/original/file-20230214-30-ka8so1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=374&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/510222/original/file-20230214-30-ka8so1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=374&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/510222/original/file-20230214-30-ka8so1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=470&fit=crop&dpr=1 754w, https://images.theconversation.com/files/510222/original/file-20230214-30-ka8so1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=470&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/510222/original/file-20230214-30-ka8so1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=470&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The 6.9 magnitude Loma Prieta earthquake in 1989 caused widespread damage around the Bay Area and dozens of deaths.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/oakland-ca-october-17-1989-two-people-lower-right-comfort-news-photo/1172229915">Paul Miller/MediaNews Group/Oakland Tribune via Getty Images</a></span>
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<h2>Are there any hints a quake could be coming?</h2>
<p>Only about 1 in 20 damaging earthquakes have foreshocks – <a href="https://www.usgs.gov/faqs/what-probability-earthquake-foreshock-larger-earthquake">smaller quakes that precede a larger one</a> in the same place. By definition they aren’t foreshocks, though, until a bigger one follows. The inability to recognize whether an earthquake in isolation is a foreshock is a big part of why useful prediction still eludes us.</p>
<p>However, in the past decade or so, there have been a number of massive earthquakes of magnitude 8 or more, including the <a href="https://earthquake.usgs.gov/earthquakes/eventpage/official20110311054624120_30/origin/detail?source=us&code=usp000hvnu">2011 magnitude 9.0 Tohoku earthquake and tsunami in Japan</a> and a <a href="https://earthquake.usgs.gov/earthquakes/eventpage/usc000nzvd/executive#summary">2014 magnitude 8.1 in Chile</a>. Interestingly, a larger fraction of those very biggest earthquakes seem to have <a href="https://doi.org/10.1126/science.1256074">exhibited some precursory events</a>, either in the form of <a href="https://doi.org/10.1126/science.1255202">a series of foreshocks detected by seismometers</a> or <a href="https://doi.org/10.1126/science.1215141">sped-up movements of the nearby Earth’s crust</a> detected by GPS stations, called “slow slip events” by earthquake scientists.</p>
<p>These observations suggest perhaps there really are precursory signals for at least some huge quakes. Maybe the sheer size of the ensuing quake made otherwise imperceptible changes in the region of the fault prior to the main event more detectable. We don’t know, because so few of these greater than magnitude 8 earthquakes happen. Scientists don’t have a lot of examples to go on that would let us test hypotheses with statistical methods.</p>
<p>In fact, while earthquake scientists all agree that we can’t predict quakes today, there are <a href="https://press.princeton.edu/books/paperback/9780691173306/predicting-the-unpredictable">now essentially two camps</a>: In one view, earthquakes are the result of complex cascades of tiny effects – a sensitive chain reaction of sorts that starts with the <a href="https://science.howstuffworks.com/math-concepts/butterfly-effect.htm">proverbial butterfly wing flapping</a> deep within a fault – so they’re inherently unpredictable and will always remain so. On the other hand, some geophysicists believe we may one day unlock the key to prediction, if we can just find the right signals to measure and gain enough experience.</p>
<h2>How do early warning systems work?</h2>
<p>One real breakthrough today is that scientists have developed earthquake early warning systems like the <a href="https://pnsn.org/pnsn-data-products/earthquake-early-warning">USGS ShakeAlert now operating</a> in California, Oregon and Washington state. These systems can send out an alert to residents’ mobile devices and to operators of critical machinery, including utilities, hospitals, trains and so on, providing warning of anywhere from a few seconds to more than a minute before shaking begins.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/510224/original/file-20230214-20-m5xy8p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="one person buries something in the ground while another watches" src="https://images.theconversation.com/files/510224/original/file-20230214-20-m5xy8p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/510224/original/file-20230214-20-m5xy8p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/510224/original/file-20230214-20-m5xy8p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/510224/original/file-20230214-20-m5xy8p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/510224/original/file-20230214-20-m5xy8p.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/510224/original/file-20230214-20-m5xy8p.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/510224/original/file-20230214-20-m5xy8p.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A seismologist installs monitoring equipment that will track any earthquake movement.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/seismologist-joao-fontiela-installs-a-seismograph-to-news-photo/1239547561">Patricia De Melo Moreira/AFP via Getty Images</a></span>
</figcaption>
</figure>
<p>This sounds like earthquake prediction, but it is not. Earthquake early warning relies on networks of seismometers that detect the very beginning of an earthquake on a fault and automatically calculate its location and magnitude before the damaging waves have spread very far. The sensing, calculating and data transfer all happen near the speed of light, while the seismic waves move more slowly. That time difference is what allows early warning.</p>
<p>For example, if an earthquake begins off the coast of Washington state beneath the ocean, coastal stations can detect it, and cities like Portland and Seattle could get tens of seconds of warning time. People may well get enough time to take a life safety action like “<a href="https://www.shakeout.org/dropcoverholdon/">Drop, Cover and Hold On</a>” – as long as they are sufficiently far away from the fault itself.</p>
<h2>What complications would predicting bring?</h2>
<p>While earthquake prediction has often been referred to as the “holy grail” of seismology, it actually would present some real dilemmas if ever developed.</p>
<p>First of all, earthquakes are so infrequent that any early methods will inevitably be of uncertain accuracy. In the face of that uncertainty, who will make the call to take a major action, such as evacuating an entire city or region? How long should people stay away if a quake doesn’t materialize? How many times before it’s a boy-who-cried-wolf situation and the public stops heeding the orders? How do officials balance the known risks from the <a href="https://www.chron.com/news/houston-texas/houston/article/Hurricane-Rita-anxiety-leads-to-hellish-fatal-6521994.php">chaos of mass evacuation</a> against the risk from the shaking itself? The idea that prediction technology will emerge fully formed and reliable is a mirage. </p>
<p>It is often said in the field of seismology that <a href="https://theconversation.com/earthquakes-dont-kill-people-buildings-do-and-those-lovely-decorative-bits-are-the-first-to-fall-168476">earthquakes don’t kill people, buildings do</a>. Scientists are already good enough today at forecasting earthquake hazards that the best course of action is to redouble efforts to construct or retrofit buildings, bridges and other infrastructure so they’re safe and resilient in the event of ground shaking in any area known to be at risk from large future quakes. These precautions will pay off in lives and property saved far more than a hoped-for means of earthquake prediction, at least for the foreseeable future.</p>
<p><em>This is an updated version of an article originally published on Feb. 15, 2023.</em></p><img src="https://counter.theconversation.com/content/199666/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Harold Tobin receives funding from the National Science Foundation and the U.S. Geological Survey. </span></em></p>The idea that scientists could warn a region that a big quake was coming at a certain time – with enough advance notice for large-scale preparation and evacuation – remains a dream, not a reality.Harold Tobin, Professor of Seismology and Geohazards, University of WashingtonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1347042020-03-31T12:23:51Z2020-03-31T12:23:51ZHow we discovered the conditions behind 'slow earthquakes’ that happen over weeks or even months – new research<figure><img src="https://images.theconversation.com/files/324122/original/file-20200330-172185-1ayx6cq.jpg?ixlib=rb-1.1.0&rect=20%2C1%2C964%2C564&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The world's tectonic plates.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/tectonic-plates-move-constantly-making-new-1386802979">Naeblys/Shutterstock</a></span></figcaption></figure><p>You’re probably familiar with earthquakes as relatively short, sharp shocks that can shake the ground, topple buildings and tear rips in the Earth. These earthquakes, and their aftershocks, happen because although tectonic plates move at centimetres per year, this motion is seldom steady. Earthquakes result from a <a href="https://earthquake.usgs.gov/learn/glossary/?term=stick-slip">“stick-slip”</a> motion, where rocks “stick” along fault planes while stress accumulates until a “slip” occurs – a bit like pulling on a stuck door until it suddenly opens. This slip also releases energy as the seismic waves that, in large magnitude earthquakes, create substantial damage. </p>
<p>In the last two decades another class of stick-slip motion <a href="https://www.smithsonianmag.com/science-nature/slow-earthquakes-are-thing-180960248/">has been discovered worldwide</a>. These “slow slip events” last for weeks to months, compared to seconds to minutes for earthquakes. Slow slip events occur faster than average plate motion, but too slow to generate measurable seismic waves. This means they need to be <a href="https://www.earthmagazine.org/article/precise-fault-how-gps-revolutionized-seismic-research">studied by GPS networks</a> rather then seismometers.</p>
<p>Although their motion is slow, the amount of movement that occurs in a slow slip event is substantial. Earthquake magnitude <a href="https://www.usgs.gov/natural-hazards/earthquake-hazards/science/earthquake-magnitude-energy-release-and-shaking-intensity">depends on the distance that rocks move and the area this movement occurs over</a>. Using the same definition, many slow slip events would have had <a href="https://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=12225573">magnitudes above 7.0</a> if they slipped at earthquake speeds. </p>
<p>Slow slip events repeat at intervals of a year to a few years. Compared to major earthquakes, which have repeat times of hundreds of years (or more), slow slip events <a href="http://www.eri.u-tokyo.ac.jp/project/sloweq/en/newsletters/pdf/leaflet_EN.pdf">are actually very frequent</a>. Even in the short time of a couple of decades that we’ve observed these types of slip, many cycles have occurred in several places – <a href="https://www.annualreviews.org/doi/full/10.1146/annurev-earth-040809-152531">notably around the Pacific Rim</a>. </p>
<p>Slow slip events generally happen next to areas where faults <a href="https://earthquake.usgs.gov/learn/glossary/?term=locked%20fault">are locked</a> and expected to rupture in major earthquakes. It’s therefore possible that these slow slip events <a href="https://science.sciencemag.org/content/353/6296/253?rss=1">can trigger earthquakes on neighbouring locked faults</a>. It has, for example, been suggested that slow slip events preceded the <a href="https://science.sciencemag.org/content/351/6272/488">2011 magnitude 9.1 Tohoku earthquake in Japan</a> and the <a href="https://science.sciencemag.org/content/345/6201/1165">2014 magnitude 8.1 Iquique earthquake in Chile</a>. That said, numerous slow slip events have also been observed without any immediate, subsequent major earthquakes on neighbouring faults.</p>
<p>Earthquakes may also trigger slow slip. In particular, the magnitude 7.8 Kaikōura earthquake in New Zealand in 2016 <a href="https://www.eastcoastlab.org.nz/news/kaikoura-quake-triggered-widespread-slow-slip-events/">triggered slow slip events</a> up to 600km away from its epicentre. </p>
<p>It is not known why some fault segments host slow slip and others host earthquakes. Neither is it known whether the same area can change behaviour and host either slow slip or earthquakes at different times. It’s therefore important to characterise the source of slow slip, and find out what materials help create slow slip and under what conditions.</p>
<h2>A unique opportunity</h2>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/324238/original/file-20200331-65518-izbrkx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/324238/original/file-20200331-65518-izbrkx.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=435&fit=crop&dpr=1 600w, https://images.theconversation.com/files/324238/original/file-20200331-65518-izbrkx.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=435&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/324238/original/file-20200331-65518-izbrkx.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=435&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/324238/original/file-20200331-65518-izbrkx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=546&fit=crop&dpr=1 754w, https://images.theconversation.com/files/324238/original/file-20200331-65518-izbrkx.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=546&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/324238/original/file-20200331-65518-izbrkx.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=546&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Hikurangi subduction zone.</span>
<span class="attribution"><a class="source" href="https://www.ncei.noaa.gov/maps-and-geospatial-products">Åke Fagereng composite using map data from NOAA.</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The Hikurangi <a href="https://www.universetoday.com/43822/subduction-zone/">subduction zone</a> (where the Pacific ocean floor is pulled underneath the New Zealand continent) offshore New Zealand’s North Island <a href="https://www.gns.cri.nz/Home/Learning/Science-Topics/Earthquakes/New-Zealands-Largest-Fault">is potentially the country’s largest earthquake fault</a> and is <a href="https://www.youtube.com/watch?v=xgk2zBvdOgw">a unique opportunity</a> to <a href="https://eos.org/science-updates/investigations-of-shallow-slow-slip-offshore-of-new-zealand">investigate slow slip events</a>. This is because slow slip here happens <a href="https://science.sciencemag.org/content/352/6286/701">shallower and closer to the shoreline</a> than anywhere else in the world. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/324278/original/file-20200331-65495-16wi6qh.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/324278/original/file-20200331-65495-16wi6qh.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/324278/original/file-20200331-65495-16wi6qh.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/324278/original/file-20200331-65495-16wi6qh.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/324278/original/file-20200331-65495-16wi6qh.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/324278/original/file-20200331-65495-16wi6qh.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/324278/original/file-20200331-65495-16wi6qh.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/324278/original/file-20200331-65495-16wi6qh.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The drill.</span>
<span class="attribution"><span class="source">Åke Fagereng</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The shallow slow slip events in New Zealand have been observed by <a href="https://www.geonet.org.nz/earthquake/sse/hikurangi">onshore GPS</a> and <a href="https://cires.colorado.edu/research/research-groups/project/hobitss-hikurangi-ocean-bottom-investigation-tremor-and-slow-slip">ocean bottom pressure sensors</a>. Oceanic scientific drilling expeditions recently <a href="https://www.stuff.co.nz/national/nz-earthquake/102152802/scientists-drilling-into-the-hikurangai-trench-hope-to-find-a-hotbed-of-data">sampled sediments and installed observatories</a> along this margin. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/324120/original/file-20200330-194972-1vvsx1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/324120/original/file-20200330-194972-1vvsx1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/324120/original/file-20200330-194972-1vvsx1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=326&fit=crop&dpr=1 600w, https://images.theconversation.com/files/324120/original/file-20200330-194972-1vvsx1l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=326&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/324120/original/file-20200330-194972-1vvsx1l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=326&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/324120/original/file-20200330-194972-1vvsx1l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=409&fit=crop&dpr=1 754w, https://images.theconversation.com/files/324120/original/file-20200330-194972-1vvsx1l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=409&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/324120/original/file-20200330-194972-1vvsx1l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=409&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The subduction zone.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/plate-tectonics-tectonic-processes-interactions-plates-1090146473">Stihii/Shutterstock</a></span>
</figcaption>
</figure>
<p>These <a href="http://www.iodp.org/">International Ocean Discovery Program</a> expeditions – which drilled to just over 1km deep in water depths of 3.5km in <a href="https://joidesresolution.org/expedition/372/">late 2017</a> and <a href="https://joidesresolution.org/expedition/375/">early 2018</a> – revealed that the seafloor rocks and sediments hosting slow slip in Hikurangi are extremely variable. The range of rocks, described in a recent <a href="https://advances.sciencemag.org/content/6/13/eaay3314">Science Advances paper</a> led by Philip Barnes of <a href="https://niwa.co.nz/">NIWA</a> (New Zealand’s National Institute of Water and Atmospheric Research), include mudstones, sands, carbonates, and sedimentary deposits from oceanic volcanic eruptions. The seafloor samples show that the source of the slow slip is a mixture of very soft sediment and hard, solid rocks. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/324269/original/file-20200331-65543-1mabwvn.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/324269/original/file-20200331-65543-1mabwvn.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/324269/original/file-20200331-65543-1mabwvn.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/324269/original/file-20200331-65543-1mabwvn.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/324269/original/file-20200331-65543-1mabwvn.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/324269/original/file-20200331-65543-1mabwvn.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/324269/original/file-20200331-65543-1mabwvn.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/324269/original/file-20200331-65543-1mabwvn.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Different types of rock from the New Zealand seafloor.</span>
<span class="attribution"><span class="source">Åke Fagereng</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The diverse seafloor sediments are not the only variability offshore of New Zealand. The seafloor itself is also very rough, including <a href="https://www.whoi.edu/know-your-ocean/ocean-topics/seafloor-below/seamounts/">seamounts</a> (submarine mountains rising over a kilometre above the seafloor). This <a href="https://www.sciencedirect.com/science/article/abs/pii/S0012821X14002313">seafloor roughness also makes the fault vary</a> depending on where along it you are. </p>
<p>The observations are consistent with a <a href="https://www.nature.com/articles/ngeo2490">hypothesis</a> where slow slip events occur in rocks that are <a href="https://www.nature.com/articles/ncomms11104">transitional between moving steadily and moving in earthquakes</a>. One way to think of this model is as <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GC008481">rigid rocks interacting with softer, more ductile</a> surroundings. Researchers using <a href="https://www.sciencedirect.com/science/article/abs/pii/S0040195117304596">numerical simulations</a> and <a href="https://www-sciencedirect-com.abc.cardiff.ac.uk/science/article/pii/S0040195119300459?via%3Dihub">laboratory experiments</a> have also suggested that variable fault rocks can cause slow slip.</p>
<p>But diverse fault rock isn’t the only model for the mechanics of slow slip. Another possibility is that <a href="https://www.nature.com/articles/s41561-019-0367-x">pressurised fluids decrease frictional resistance and slip speed along faults</a>. It is also possible that some rocks become stronger when they move faster – so that <a href="https://science.sciencemag.org/content/341/6151/1229">faults start accelerating but slow down before reaching earthquake speeds</a>. </p>
<p>The recent discoveries in New Zealand may be applicable to other depths and locations around the world. However, future studies will undoubtedly lead to further insights and complexities – including in the relationship between slow slip events and earthquakes.</p><img src="https://counter.theconversation.com/content/134704/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Åke Fagereng receives funding from the European Research Council, the Natural Environment Research Council (UK) and the Engineering and Physical Sciences Research Council (UK). </span></em></p>Earthquakes happen over seconds to minutes. Slow slip events on the other hand can last for weeks or months.Åke Fagereng, Reader, School of Earth and Ocean Sciences, Cardiff UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1234282020-01-06T12:06:32Z2020-01-06T12:06:32ZA new way to identify a rare type of earthquake in time to issue lifesaving tsunami warnings<figure><img src="https://images.theconversation.com/files/308024/original/file-20191219-11946-1t4d9ok.jpg?ixlib=rb-1.1.0&rect=350%2C0%2C5065%2C3700&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">This unusual earthquake type generates an outsized tsunami. </span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/1fEYDfuGli0">camila castillo/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Just a few times in a century, somewhere on the globe, a rare “tsunami earthquake” occurs. These are mysterious because, while they’re just medium-sized as earthquakes go, they cause disproportionately large and devastating tsunamis. This type of midsized earthquake is very different than an event like the <a href="http://www.tectonics.caltech.edu/outreach/highlights/sumatra/what.html">2004 earthquake in Sumatra</a> – a very big magnitude 9.2 event which unsurprisingly produced a huge tsunami.</p>
<p>The most recent tsunami earthquake happened in 2010. <a href="https://doi.org/10.1029/2010GL046552">A magnitude 7.8 earthquake</a> <a href="http://itic.ioc-unesco.org/index.php?option=com_content&view=article&id=1673:301&catid=1444&Itemid=1444">off the Mentawai Islands in Indonesia</a> <a href="https://doi.org/10.1029/2010GL046498">set off a tsunami</a> that was <a href="https://doi.org/10.1029/2012JB009159">over 50 feet in height</a> in some places – much greater than seismologists would predict based just on the earthquake’s size. <a href="https://earthobservatory.sg/outreach/natural-hazard-outreach/west-sumatra-tectonics-and-tsunami-hazard">509 people were killed</a>, and 15,000 more were displaced or left homeless. </p>
<p>Tsunami earthquakes are particularly destructive and dangerous because the massive tsunami waves can hit local coastal communities within just five to 15 minutes – before officials can issue a warning. But <a href="https://doi.org/10.1029/2019GL083989">based on our analysis</a> of previously unavailable closeup observations of the 2010 Mentawai event, my colleagues <a href="https://scholar.google.com/citations?user=8YD_3R8AAAAJ&hl=en&oi=ao">and I</a> think there is a way to determine that an event is a tsunami earthquake in time to warn people that an unexpectedly large wave is on the way.</p>
<h2>Earthquakes under the ocean</h2>
<p>The Earth’s surface is made up of <a href="https://theconversation.com/plate-tectonics-new-findings-fill-out-the-50-year-old-theory-that-explains-earths-landmasses-55424">floating tectonic plates</a> that fit together like a slightly imperfect jigsaw puzzle. These plates are moving next to, under or away from each other.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=372&fit=crop&dpr=1 600w, https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=372&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=372&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=467&fit=crop&dpr=1 754w, https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=467&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/308389/original/file-20200102-11904-tusj3g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=467&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An earthquake along a subduction zone happens when the leading edge of the overriding plate breaks free and springs seaward, raising the seafloor and the water above it. This uplift starts a tsunami.</span>
<span class="attribution"><a class="source" href="https://www.usgs.gov/media/images/earthquake-starts-tsunami">USGS</a></span>
</figcaption>
</figure>
<p>In <a href="https://www.livescience.com/43220-subduction-zone-definition.html">a subduction zone</a>, one tectonic plate is sinking beneath another. This builds up stresses over time and will eventually create an earthquake. Most typical subduction-zone earthquakes occur roughly 10 to 30 miles down, in an area where the rocks are rigid and strong on the fault between the two tectonic plates.</p>
<p>Meanwhile, the shallowest area of a subduction zone, closest to the seafloor, is made up of soft sediments that are not very strong. Earthquakes rarely occur only here, because stresses mostly don’t build up in these soft, weak rocks.</p>
<p>Geoscientists define an earthquake’s overall size with its magnitude. Earthquake magnitude describes how much “work” is accomplished by the earthquake moving the fault – more work for either more movement, or for moving more rigid rock.</p>
<p>Very large earthquakes, like the magnitude 9 Tohoku earthquake in Japan in 2011, are so big that they break the deeper part of the subduction zone, but also continue upwards to break the shallow part of a subduction zone. This rapid earthquake motion moves the seafloor and <a href="https://www.iris.edu/hq/inclass/animation/subduction_zone_tsunamis_generated_by_megathrust_earthquakes">creates a tsunami</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=267&fit=crop&dpr=1 600w, https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=267&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=267&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=336&fit=crop&dpr=1 754w, https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=336&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/293875/original/file-20190924-51434-1ytyrz6.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=336&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Cartoon depicting the amount of movement in five earthquakes. The 2010 Mentawai tsunami earthquake moved the fault much more – over 65 feet compared to about 15 feet for the others – and the movement occurred much closer to the seafloor than in any of the other earthquakes.</span>
<span class="attribution"><span class="source">Sahakian et al. (2019), GRL</span></span>
</figcaption>
</figure>
<h2>What sets tsunami quakes apart</h2>
<p>“Tsunami earthquakes” are strange in that they happen almost entirely in the soft, weak section of the fault.</p>
<p>Because tsunami earthquakes break such soft rock, they happen slower, and create much more movement on or near the seafloor in comparison to a normal subduction-zone earthquake of the same size that happens in rigid rock. This in turn creates a much larger tsunami than expected. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=314&fit=crop&dpr=1 600w, https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=314&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=314&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=395&fit=crop&dpr=1 754w, https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=395&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/306913/original/file-20191214-85412-1b87exs.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=395&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Seismograms showing how much the ground shook from six similarly sized earthquakes, at seismometers all about the same distance from their earthquake. You’d expect the shaking to be comparable. The 2010 Mentawai earthquake seismogram is at the bottom in orange, and shows significantly less shaking than any of the others.</span>
<span class="attribution"><span class="source">Modified from Sahakian et al. (2019), GRL.</span></span>
</figcaption>
</figure>
<p>A tsunami earthquake might have the same magnitude as an earthquake that occurs in rigid rock but produces much less of what seismologists call high-frequency energy. </p>
<p>Think of breaking a thick slab of concrete – which is strong and would produce an audible bang with both low and high-pitched noise – versus breaking a loaf of bread, which makes almost no sound at all. In the Earth, “sound” is the shaking you feel under your feet. The soft bread break is like a tsunami earthquake that doesn’t release a lot of high-frequency energy, and thus doesn’t create as much shaking as we would expect for its magnitude.</p>
<h2>Sensing quakes in time to warn</h2>
<p>Currently, officials rely on knowing an earthquake’s magnitude and location to issue tsunami warnings within tens of minutes. But this doesn’t work in the case of tsunami earthquakes, because the earthquake’s magnitude doesn’t match up with the size of the tsunami it produces.</p>
<p>Instead, to figure out whether an earthquake is in fact a tsunami earthquake, scientists compare its seismic magnitude measured from afar with the amount of high frequency radiated energy it produced, as recorded by far away stations.</p>
<p>If the ratio of energy to magnitude is very low, it’s a tsunami earthquake – basically, its shaking was far too weak for its magnitude because it was breaking soft rock. Instead, its energy is of the low-frequency type: Rather than strong shaking, its energy goes into large slow movement of the seafloor and the ensuing tsunami.</p>
<p>The problem is that in the past, scientists had never recorded one of these elusive earthquakes closeup in what we call the near-field – within about 180 miles (300 kilometers) or so. Instead, scientists have had to find an earthquake’s energy-to-magnitude ratio using seismic waves that have traveled all the way from the epicenter of the earthquake across the world to where researchers can measure them. This process is relatively slow, so we haven’t been able to identify tsunami earthquakes quickly enough to warn people in time, before the wave hits the coast.</p>
<p>Now my colleagues and I have for the first time analyzed data recorded by seismic stations that happened to be near the epicenter of the 2010 Mentawai earthquake. We think we have figured out a new way to identify the danger of a future tsunami earthquake, faster.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/308439/original/file-20200103-11951-8wlrvt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Tsunamis can take a terrible toll, as for this Indonesian family that lost their father and their home in the Mentawai disaster.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Indonesia-Disasters/77a6343c59ee46199456933fc238e848/4/0">AP Photo/Tundra Laksamana</a></span>
</figcaption>
</figure>
<h2>Closer and quicker proxies</h2>
<p>Our new study used the same concept of comparing the energy released by an earthquake to its seismic magnitude – but based on data from geographically close to the event. Instead of looking at energy measurements recorded at a distance, we used two proxies.</p>
<p>To look directly at how much the ground shook, we used seismic stations onshore near the epicenters of 16 earthquakes, including the Mentawai one in 2010. Because the amount the ground accelerates when seismic waves pass through illustrates how much high frequency energy is in the earthquake, this information was a stand-in for the data we would traditionally get from the far-flung teleseismic stations. Low accelerations mean little high frequency energy.</p>
<p>For the normal earthquakes we looked at, the accelerations from near-field seismometers were close to what we’d expect for each earthquake’s magnitude. In comparison, the 2010 Mentawai earthquake’s accelerations were closer to what we would expect for a magnitude 6.3 earthquake – whereas the earthquake was actually a magnitude 7.8, and produced a tsunami we’d expect for an event of greater than magnitude 8.</p>
<p>We also looked at GPS stations close to the earthquakes. They can show us how much the ground actually moved or was displaced, and measure the earthquake magnitude itself.</p>
<p>Using these measurements together allowed us to compare the amount of energy in the earthquake with respect to its magnitude – without waiting for the seismic waves to travel across the globe. Instead, we would have been able to identify a tsunami earthquake immediately by looking at how low the accelerations were on local seismometers in comparison to the magnitude of the earthquake based on GPS readings.</p>
<p>We think our finding is really promising because these near-field measurements are available immediately – even while an earthquake is happening. Seismologists could use this approach in the future, to identify a tsunami earthquake right after it happens, and provide warning to the nearby coast before the tsunami wave arrives.</p>
<p>[ <em>Deep knowledge, daily.</em> <a href="https://theconversation.com/us/newsletters?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=deepknowledge">Sign up for The Conversation’s newsletter</a>. ]</p><img src="https://counter.theconversation.com/content/123428/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Valerie Sahakian does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A tricky kind of earthquake that happens in the soft rock of the ocean floor causes much larger tsunamis than their magnitude would predict. New research pinpoints a way to identify the danger fast.Valerie Sahakian, Assistant Professor of Geophysics, University of OregonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1167682019-05-13T15:07:50Z2019-05-13T15:07:50ZThe moon is still geologically active, study suggests<figure><img src="https://images.theconversation.com/files/273963/original/file-20190512-183096-u3nv9u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The International Space station transits the "Blue moon" in late June 2015.</span> <span class="attribution"><a class="source" href="http://apod.nasa.gov/apod/ap150731.html">Dylan O'Donnell</a></span></figcaption></figure><p>We tend to think of the moon as the archetypal “dead” world. Not only is there no life, almost all its volcanic activity <a href="http://volcano.oregonstate.edu/oldroot/volcanoes/planet_volcano/lunar/Overview.html">died out billions of years ago</a>. Even the youngest lunar lava is old enough to have become scarred by numerous impact craters that have been collected over the aeons as cosmic debris crashed into the ground.</p>
<p>Hints that the moon is not quite geologically dead though have been around since the Apollo era, 50 years ago. Apollo missions 12, 14, 15 and 16 <a href="https://moon.nasa.gov/resources/13/apollo-11-seismic-experiment/">left working “moonquake detectors”</a> (seismometers) on the lunar surface. These transmitted recorded data to Earth until 1977, showing vibrations caused by internal “moonquakes”. But no one was sure whether any of these were associated with actual moving faults breaking the surface of the moon or purely internal movements that could also cause tremors. Now a new study, <a href="https://www.nature.com/articles/s41561-019-0362-2">published in Nature Geoscience</a>, suggests the moon may indeed have active faults today.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/273346/original/file-20190508-183112-vgh97g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/273346/original/file-20190508-183112-vgh97g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/273346/original/file-20190508-183112-vgh97g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=354&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273346/original/file-20190508-183112-vgh97g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=354&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273346/original/file-20190508-183112-vgh97g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=354&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273346/original/file-20190508-183112-vgh97g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=445&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273346/original/file-20190508-183112-vgh97g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=445&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273346/original/file-20190508-183112-vgh97g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=445&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The seismometer deployed on the moon by Apollo 14 (nearest of the three instruments).</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>Another clue that something is still going on at the moon came in 1972 when Apollo 17 astronauts <a href="https://www.nasa.gov/astronautprofiles/cernan">Gene Cernan</a> and <a href="https://www.space.com/39009-apollo-17-astronaut-harrison-schmitt-interview.html">Jack Schmitt</a> inspected a step in the terrain, a few tens of metres high, that they called “the <a href="https://airandspace.si.edu/multimedia-gallery/web11563-2010hjpg">Lee-Lincoln scarp</a>”. They, and their team of advisers back on Earth thought it might be a geological fault (where one tract of crustal rock has moved relative to another), but they weren’t sure.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/273376/original/file-20190508-183089-cyek8x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/273376/original/file-20190508-183089-cyek8x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/273376/original/file-20190508-183089-cyek8x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=606&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273376/original/file-20190508-183089-cyek8x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=606&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273376/original/file-20190508-183089-cyek8x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=606&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273376/original/file-20190508-183089-cyek8x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=762&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273376/original/file-20190508-183089-cyek8x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=762&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273376/original/file-20190508-183089-cyek8x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=762&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Lee-Lincoln scarp sweeping across the valley floor and making a turn as it cuts up the valley side on the right.</span>
<span class="attribution"><span class="source">NASA Apollo 17 image library (frame AS17-137-20897)</span></span>
</figcaption>
</figure>
<p>A handful of similar examples were noted in photographs taken from Apollo craft as they orbited near the moon’s equator, but it was not until 2010 that the <a href="https://www.lroc.asu.edu/">Lunar Reconniassance Orbiter Camera</a>, capable of recording details less than a metre across, revealed that such scarps can be found scattered across the whole globe. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/273353/original/file-20190508-183093-nd32s5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/273353/original/file-20190508-183093-nd32s5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/273353/original/file-20190508-183093-nd32s5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=537&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273353/original/file-20190508-183093-nd32s5.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=537&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273353/original/file-20190508-183093-nd32s5.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=537&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273353/original/file-20190508-183093-nd32s5.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=674&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273353/original/file-20190508-183093-nd32s5.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=674&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273353/original/file-20190508-183093-nd32s5.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=674&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A 3.5km wide view of part of the moon disturbed by faults.</span>
</figcaption>
</figure>
<p>It is now widely agreed that these are thrust faults, caused as the moon cools down from <a href="https://theconversation.com/how-old-is-our-moon-71036">its hot birth</a>. As it does, “thermal contraction” causes its volume to shrink and compresses the surface. That means that <a href="https://www.nasa.gov/mission_pages/LRO/news/shrinking-moon.html">the moon is shrinking slightly</a>. However, thrust faults don’t necessarily have to be active and moving, causing more further tremors. The same thing has been happening on Mercury on a far grander scale, where the planetary radius has shrunk by 7km during the past 3m years. There, the biggest scarps are nearly a hundred times larger than those on the moon.</p>
<h2>Active faults</h2>
<p>Analysis shows that these faults are relatively young, not older than about 50m years. But are they active and still moving today? In the new study, <a href="https://airandspace.si.edu/people/staff/thomas-watters">Tom Watters of the Smithsonian Institution</a> in the US and colleagues employed a new way to pinpoint the locations of the near-surface moonquakes in the Apollo data more precisely than was previously possible. </p>
<p>The team discovered that of the 28 detected shallow quakes, eight are close to (within 30km of) fault scarps, suggesting these faults may indeed be active. Six of them happened when the moon was almost at the greatest distance from Earth in its orbit. At this point, the contraction stress across the surface would be expected to peak, and quakes most likely to be triggered.</p>
<p>The team also investigated fresh looking tracks left by boulders that have been dislodged. This was presumably a result of the ground shaking, because they are also seen close to fault scarps – and have rolled or bounced down a slope. There are also traces of landslide deposits. This, they say, all adds up to a strong case that fault movements are still occurring on the moon.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/273349/original/file-20190508-183106-110pbgj.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/273349/original/file-20190508-183106-110pbgj.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/273349/original/file-20190508-183106-110pbgj.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=502&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273349/original/file-20190508-183106-110pbgj.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=502&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273349/original/file-20190508-183106-110pbgj.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=502&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273349/original/file-20190508-183106-110pbgj.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=631&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273349/original/file-20190508-183106-110pbgj.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=631&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273349/original/file-20190508-183106-110pbgj.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=631&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The tracks of two boulders that rolled downhill towards the Apollo 17 landing site. Each boulder is at the southern end of its track, where it casts a shadow to its left.</span>
<span class="attribution"><span class="source">NASA/GSFC/Arizona State University</span></span>
</figcaption>
</figure>
<p>So does this mean that the moon is unsafe for human exploration? The US recently <a href="https://theconversation.com/us-wants-a-crewed-mission-to-the-moon-in-five-years-but-can-and-should-that-be-done-114951">announced plans to go there</a> in the next five years, with the aim to set up a lunar base. Luckily, none of the new findings mean that the moon is a hotbed of ground tremors. Moonquakes are rarer and weaker than on Earth, but there are definitely a few places close to the faults where it might be best to avoid when it comes to planning moon bases.</p><img src="https://counter.theconversation.com/content/116768/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Rothery is co-leader of the European Space Agency's Mercury Surface and Composition Working Group, and a Co-Investigator on MIXS (Mercury Imaging X-ray Spectrometer) that is now on its way to Mercury on board the European Space Agency's Mercury orbiter BepiColombo. He has received funding from the UK Space Agency and the Science & Technology Facilities Council for work related to Mercury BepiColombo, and is currently funded by the European Commission under its Horizon 2020 programme for work on planetary geological mapping (776276 Planmap). He is author of Planet Mercury - from Pale Pink Dot to Dynamic World (Springer, 2015), Moons: A Very Short Introduction (Oxford University Press, 2015) and Planets: A Very Short Introduction (Oxford University Press, 2010). He is Educator on the Open University's free learning Badged Open Course (BOC) on Moons and its equivalent FutureLearn Moons MOOC, and chair of the Open University's level 2 course on Planetary Science and the Search for Life.</span></em></p>New analysis of data from the Apollo era shows that moonquakes occur close to visible faults, which may matter when setting up a moon base.David Rothery, Professor of Planetary Geosciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/874802017-11-16T01:40:45Z2017-11-16T01:40:45ZAfter Iran-Iraq earthquake, seismologists work to fill in fault map of the region<figure><img src="https://images.theconversation.com/files/194935/original/file-20171116-19823-1vceqr2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Earthquake survivors are living in tents in western Iran.</span> <span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Iran-Iraq-Earthquake/8d1afd6e4be24f2ba87f19b3e9a4997e/2/0">AP Photo/Vahid Salemi</a></span></figcaption></figure><p>With a <a href="https://earthquake.usgs.gov/earthquakes/eventpage/us2000bmcg#executive">magnitude of 7.3</a>, the <a href="https://www.nytimes.com/2017/11/13/world/middleeast/iran-iraq-earthquake.html">Nov. 12, 2017 earthquake</a> that shook the border region between Iran and Iraq is among the largest ever recorded in this area. Seismologists know it resulted from the pressure built up between the colliding Arabian and Eurasian plates of the Earth’s crust. But there’s still a lot for researchers to uncover about seismic activity in the region.</p>
<p><iframe id="tc-infographic-126" class="tc-infographic" height="400px" src="https://cdn.theconversation.com/infographics/126/cf6b3e9d59efdac5c40fa6c375504b22d941c754/site/index.html" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Originally from Iran, I’m a seismologist who studies earthquakes, tsunamis and landslides. I’ve been thinking a lot about potential seismic activity and the consequent hazard in this area. My earth sciences colleagues have been <a href="https://doi.org/10.1111/j.1365-246X.1990.tb06579.x">examining these faults</a> for years in order to better understand the <a href="https://doi.org/10.1016/0040-1951(94)00185-C">fault systems in the region</a>. However, the Earth sometimes surprises us, and this time the rupture did not happen on a previously known major fault.</p>
<p>Our lack of knowledge about the specific fault causing this earthquake is mainly because seismologists know only about faults that have already caused earthquakes. Only after new earthquakes can we update our fault maps to be more complete. It’s learning from past earthquakes that lets us better understand and prepare for future seismic hazards.</p>
<h2>Tectonic plates in motion</h2>
<p>The outer rigid surface of the Earth is divided into chunks known as tectonic plates. These plates move around at the rate of a few centimeters per year – by coincidence, the same rate at which your fingernails grow. The Arabian Peninsula and Iran are on separate adjacent plates in this region.</p>
<p>The mostly northward continental collision between the Arabian plate and Eurasia (which includes Iran) has created the Zagros mountains as the plates crash together in slow motion. Collision energy is also released in the form of earthquakes at fault lines along or close to these boundaries. Many researchers are studying what portions of this region’s collision energy are <a href="https://doi.org/10.1111/j.1365-246X.1990.tb06579.x">spent building mountains versus causing earthquakes</a>.</p>
<p>Seismologists do know the Zagros mountains host many active fault lines, and the tectonic wiggles on these faults cause a significant number of earthquakes in Iran and Iraq. In fact, about <a href="http://irsc.ut.ac.ir/">25,000 earthquakes have been recorded</a> in the Zagros mountains over just the past 11 years. Although these earthquakes are usually small in size, the data show that every now and then moderate to large events also occur; these can result in significant destruction.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/194692/original/file-20171114-30038-iyiuuq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/194692/original/file-20171114-30038-iyiuuq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/194692/original/file-20171114-30038-iyiuuq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=426&fit=crop&dpr=1 600w, https://images.theconversation.com/files/194692/original/file-20171114-30038-iyiuuq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=426&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/194692/original/file-20171114-30038-iyiuuq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=426&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/194692/original/file-20171114-30038-iyiuuq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=535&fit=crop&dpr=1 754w, https://images.theconversation.com/files/194692/original/file-20171114-30038-iyiuuq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=535&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/194692/original/file-20171114-30038-iyiuuq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=535&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Recorded earthquakes in the region are marked with gray circles. Major fault lines are in blue, with the Nov. 12 epicenter marked by a star.</span>
<span class="attribution"><span class="source">Amir Salaree</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The main fault responsible for the Nov. 12 earthquake has yet to be identified. As located by the Iranian Seismological Center, the quake took place in a zone between two major known faults: the High Zagros Fault and the Mountain Front Fault.</p>
<p>One good thing that comes from a big earthquake is more data about the structure of tectonic plates and therefore the seismic potential in the area. Researchers and planners can in turn use this information to prepare for future events. As the saying goes, we cannot predict earthquakes, but we can anticipate them.</p>
<h2>What was different about this quake</h2>
<p>Large earthquakes in Iran have typically caused a high number of fatalities. The <a href="https://doi.org/10.1093/gji/ggv044">1990 Rudbar</a> (magnitude 7.4) and <a href="http://www.iranicaonline.org/articles/bam-earthquake-2003">2003 Bam</a> (magnitude 6.6) earthquakes resulted in a total of around 55,000 deaths and as much as US$9 billion of economic loss.</p>
<p>According to the Iranian state-run news agency, the Nov. 12 earthquake <a href="http://english.alarabiya.net/en/News/middle-east/2017/11/15/Survivors-of-Iran-quake-await-badly-needed-aid-3-days-later.html">killed over 500 people</a>, as of this publication, with thousands injured, mostly on the Iranian side of the border. Registering a magnitude of 7.3, the quake was comparable in size to its 1990 and 2003 counterparts, but produced a relatively low number of casualties. This was due to several important factors.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/194936/original/file-20171116-19823-1d1rh84.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/194936/original/file-20171116-19823-1d1rh84.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/194936/original/file-20171116-19823-1d1rh84.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/194936/original/file-20171116-19823-1d1rh84.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/194936/original/file-20171116-19823-1d1rh84.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/194936/original/file-20171116-19823-1d1rh84.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/194936/original/file-20171116-19823-1d1rh84.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/194936/original/file-20171116-19823-1d1rh84.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Even with a smaller death toll, thousands were left homeless, in need of aid and mourning those who were killed.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/APTOPIX-Iran-Iraq-Earthquake/bc828132f6e943338fce3dde21c3ce7b/5/0">AP Photo/Vahid Salemi</a></span>
</figcaption>
</figure>
<p>First, this latest earthquake was preceded by a much smaller magnitude 4.4 foreshock – a relatively smaller earthquake that precedes the largest earthquake <a href="https://earthquake.usgs.gov/learn/animations/aftershocks.php">in a series</a>. The foreshock caused many people to leave their homes and, in effect, escape the subsequent destruction. As a seismologist would tell you, earthquakes don’t kill people; buildings do.</p>
<p>Secondly, it occurred on much more rigid ground cover – mostly rocks instead of thick layers of unconsolidated soil compared to the other two events. <a href="https://earthquake.usgs.gov/hazards/urban/sfbay/soiltype/">These geological conditions</a> mean the seismic waves from the earthquake were less amplified, and so less shaking was observed on the surface.</p>
<p>Also, following the previous recent destructive earthquakes in Iran, the Iranian government <a href="http://iisee.kenken.go.jp/worldlist/26_Iran/Iran%20National%20Seismic%20Code_2007_3rd%20Version_English.pdf">passed new construction regulations</a> for more earthquake-safe buildings, calling for such things as concrete and steel frames and detailed study of the base soil prior to the construction. Considering the alarming foreshock, the smaller population in the affected towns (compared to the former two destructive earthquakes) and the unknown extent of enforcement of the building codes, it is difficult to estimate how the number of casualties would have increased in the absence of these laws.</p>
<p>For a more complete picture of this earthquake, we still need more data that are yet to be collected and documented both from field surveys and the study of seismic waves recorded by seismometers throughout the world. <a href="http://www.gsi.go.jp/cais/topic171115-index-e.html">Seismologists are looking</a> for further evidence about the propagation of the earthquake rupture to learn more about the internal characteristics of the fault as well as the properties of the convergence between the Arabian and Eurasian plates. They’ll also use seismic waves recorded from this earthquake to image the structure of Earth’s crust in the region – just like an ultrasound that provides a picture of your internal organs. </p>
<p>The aftermath of a seismic event like this one is an excellent opportunity to evaluate our understanding of earthquakes and their hazards in Iran and Iraq as well as elsewhere around the world.</p><img src="https://counter.theconversation.com/content/87480/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Amir Salaree does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The Nov. 12 earthquake wasn’t centered on any known major faults in the Earth’s crust. In its wake, scientists will collect data to add detail to what they know about seismic activity in the area.Amir Salaree, Ph.D. Candidate in Earth and Planetary Sciences, Northwestern UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/687332016-11-14T05:50:49Z2016-11-14T05:50:49ZWhat happened in New Zealand’s magnitude 7.5 earthquake<figure><img src="https://images.theconversation.com/files/145702/original/image-20161114-9083-1grxr5j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Local residents Chris and Viv Young look at damage caused by the earthquake, along State Highway One near Ward on New Zealand's South Island.</span> <span class="attribution"><span class="source">ReutersAnthony Phelps</span></span></figcaption></figure><p>At least <a href="http://www.radionz.co.nz/news/national/318000/earthquake-two-die-after-massive-tremors">two people have died</a> in the <a href="http://www.geonet.org.nz/quakes/region/newzealand/2016p858000">magnitide 7.5 earthquake</a> that struck New Zealand’s South Island early on Monday, local time. </p>
<p><a href="http://earthquake.usgs.gov/earthquakes/eventpage/us1000778i#executive">Preliminary modelling</a> suggests that the earthquake was caused by a rupture of a northeast-striking fault that projects to the surface offshore.</p>
<p>But this may be a complex event, involving several faults on the South Island.</p>
<p>The northern part of the South Island straddles the boundary between the Pacific and Australian tectonic plates.</p>
<p>The jostling between these plates pushes up rocks that create mountains including the Southern Alps and the beautiful Seaward Kaikoura Range, one of New Zealand’s <a href="http://geology.gsapubs.org/content/19/4/393.abstract">most rapidly uplifting mountain ranges</a>.</p>
<p>The plate motion forces the oceanic crust of the Pacific plate beneath the Australian plate on thrust faults, and also causes the plates to slide laterally with respect to one another on strike-slip faults. </p>
<p>The region affected by the recent earthquake has been one of the most seismically active in New Zealand over the past few years, including earthquakes that occurred as part of the <a href="https://www.gns.cri.nz/Home/Our-Science/Natural-Hazards/Recent-Events/Cook-Strait-Quakes">Cook Strait earthquake sequence in 2013</a>. It is likely that these sequences are related given their close spatial and temporal association.</p>
<h2>What slipped during the earthquake?</h2>
<p>The <a href="http://earthquake.usgs.gov/earthquakes/eventpage/us1000778i#finite-fault">preliminary analysis</a> strongly suggests that most of the energy release during this earthquake was sourced from the rupture of a roughly 200km-long fault system. This fault system is aligned northeast and dips to the northwest, beneath the northern part of the South Island. It coincides roughly with the subduction thrust in this area. </p>
<p>The potential for large earthquakes on the subduction fault in the lower North Island and upper South Island of New Zealand was recently highlighted by <a href="https://www.gns.cri.nz/">GNS Science</a>, New Zealand’s geological survey. It <a href="http://m.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11450821">published evidence</a> for two similar events in the Blenheim area roughly 520-470 years ago, and 880-800 years ago.</p>
<p>Given its setting, this latest earthquake may be structurally complex, involving a mixture of plate boundary thrusting, lateral slip on strike-slip faults, and thrusting within the Pacific plate close to the epicentre, some 15km northeast of Culverden.</p>
<p>The largest aftershocks suggest a mixture of thrusting and strike-slip movements.</p>
<h2>The damage caused by the earthquake</h2>
<p>Because the fault system was large, and the earthquake apparently started at the southwest end of the fault and propagated to the northeast, the seismic energy was released over a period of up to two minutes. </p>
<p>Large earthquakes produce more long period wave energy than smaller events. The <a href="http://www.drquigs.com/wp-content/uploads/2014/07/030113eqs060m.pdf">2011 Christchurch earthquake</a> contained a lot of high-frequency energy and very strong ground accelerations, exposing more than 300,000 people to very strong to intense ground shaking.</p>
<p>In contrast, this recent earthquake was manifested in Christchurch as lower-frequency rolling, and due to the sparse population density in the earthquake region, roughly 3,000 people in the upper South Island experienced strong ground shaking equivalent to the Christchurch earthquake.</p>
<p><a href="https://www.tvnz.co.nz/one-news/new-zealand/he-took-off-across-paddock-in-his-undies-farmer-house-faultline-reacts-staffer-bolted-moved-6m">Reports are emerging </a> of at least one major fracture in the ground surface that could be related to strike-slip faulting in the Clarence region.</p>
<p>More traces may yet be found given the complexity of the earthquake. Tide gauge analysis will help to understand if a similar trace offshore caused the tsunami. </p>
<p>The earthquake has also triggered liquefaction in coastal areas and in susceptible sediments, and landsliding of <a href="http://info.geonet.org.nz/pages/viewrecentblogposts.action?key=quake">up to a million cubic metres</a> along steep susceptible cliffs in the northern South Island. </p>
<p>There are reports of extensive road damage including in the area between <a href="http://www.newshub.co.nz/nznews/nz-quake-video-shows-road-damage-on-south-island-2016111405">Hanmer Springs and Culverden</a>, much of <a href="https://www.theguardian.com/world/gallery/2016/nov/13/new-zealand-earthquake-in-pictures">State Highway 1</a> and even <a href="https://twitter.com/JayNelson191/status/797884524013256704/photo/1?ref_src=twsrc%5Etfw">Wellington</a>, on the North Island.</p>
<p>Most of this damage is probably caused by strong ground shaking, which causes weak ground to move en masse and has resulted in numerous slips and <a href="http://www.nzta.govt.nz/traffic/roadclosures/153593">road closures</a> in the central and northern South Island. </p>
<h2>Earthquakes, aftershocks and the pull of the moon</h2>
<p>Given the earthquake happened on the eve of a <a href="https://theconversation.com/why-all-the-super-buzz-about-the-supermoon-68480">supermoon full moon</a>, and the closest the Earth and moon will be since 1948, it wasn’t long before <a href="http://www.dailymail.co.uk/news/article-3933068/New-Zealand-earthquake-predicted-eight-days-struck-blamed-supermoon.html">some tried to make a connection</a>.</p>
<p>But the tidal triggering of earthquakes <a href="https://scholar.google.co.nz/scholar?q=tidal+trigger+earthquake&btnG=&hl=en&as_sdt=0%2C5">has been investigated</a> since the 19th century and remains a challenging and controversial field.</p>
<p>Small amplitude and large wavelength tidal deformations of the Earth due to motions of the sun and moon influence stresses in Earth’s <a href="http://geology.about.com/od/platetectonics/a/About-The-Lithosphere.htm">lithosphere</a>.</p>
<p>It is possible that, for active faults that are imminently close to brittle failure, small tidal force perturbations could be enough to advance rupture relative to the earthquake cycle, or to allow a propagating rupture to travel further than it might otherwise have done.</p>
<p>But the specific time, magnitude and location of this or any other large earthquake has not been successfully predicted in the short-term using tidal stresses or any other possible precursory phenomenon.</p>
<p>Deliberately vague predictions that provide no specific information about the precise location and magnitude of a future earthquake are not predictions at all. Rather, these are hedged bets that get media air time due to the romantic misinterpretation that they were valid predictions.</p>
<p>Most earthquake scientists, including those that research tidal triggering of earthquakes, highlight the importance of preparedness over attempts at prediction when it comes to public safety.</p>
<p>To this end, GNS Science uses a system of <a href="http://info.geonet.org.nz/pages/viewrecentblogposts.action?key=quake">operational earthquake forecasts</a> to communicate earthquake risk to concerned New Zealand residents during an aftershock sequence such as we are now entering.</p>
<p>These forecasts are based on earthquake physics and statistical seismology. The <a href="http://info.geonet.org.nz/display/quake/2016/11/14/M7.5+Kaikoura+Quake%3A+What+we+know+so+far">current operational forecast</a> indicates an 80% probability of: </p>
<blockquote>
<p>A normal aftershock sequence that is spread over the next few months. Felt aftershocks (e.g. M>5) would occur from the M7.5 epicentre near Culverden, right up along the Kaikoura coastline to Cape Campbell over the next few weeks and months.</p>
</blockquote>
<p>This aftershock sequence will probably (98%) include several large aftershocks (some greater than magnitude 6 have already occurred), and for each magnitude 6 aftershock we expect 10 more magnitude 5 aftershocks over the coming days and weeks.</p><img src="https://counter.theconversation.com/content/68733/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Early analysis of the New Zealand earthquake shows it may be a complex event, involving several faults on the South Island.Brendan Duffy, Lecturer in Applied Geoscience, The University of MelbourneMark Quigley, Associate professor, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/344722015-05-01T17:54:20Z2015-05-01T17:54:20ZSeismologists deploy after a quake to learn more, so we can prepare for the next one<figure><img src="https://images.theconversation.com/files/79990/original/image-20150430-30705-10ausqo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Surface measurements hint at what's going on within.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/ctbto/15825401591">CTBTO</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><blockquote>
<p>The past is never dead. It’s not even past.
– William Faulkner</p>
</blockquote>
<p>When disasters like the <a href="http://ds.iris.edu/ds/nodes/dmc/specialevents/2015/04/25/nepal/">Nepal earthquake</a> strike, seemingly out of the blue, one can’t help but feel anguish at the mismatch between the capacity of human memory and the tenacity of denial. The simple truth about great earthquakes, and the miserable cascade of events they often trigger, is this: if an earthquake has affected a region, recently or in historical records, then future earthquakes in that region are inevitable. But, if no damaging earthquake has happened in recent memory, it’s easy to ignore the need to prepare for a future event of uncertain magnitude and proximity. The earthquake cycle is long relative to the terms of a city council, a state legislature, and even a national government.</p>
<p>As a practicing seismologist, the political questions implicit in a discussion of how much risk a society is prepared to assume relative to the costs of mitigation are largely beyond my influence. On the other hand, seismologists like me can help address the question of where earthquakes have occurred in the past – and where they will occur again in the future.</p>
<p>We can estimate how large a magnitude earthquake can be expected in a given region. We can determine <a href="http://earthquake.usgs.gov/regional/nca/soiltype/">how different substrates</a> – soils, sand, fill, bedrock – will affect ground shaking, and we can <a href="http://www.gsi.go.jp/ENGLISH/page_e30085.html">map the distribution</a> of these foundational materials on a building-by-building scale, if necessary. We can assess the propensity for <a href="http://landslides.usgs.gov">slope failure</a>, which leads to landslides. And, for some regions, we can come up with ballpark <a href="http://serc.carleton.edu/quantskills/methods/quantlit/RInt.html">estimates of the average time</a> between large-magnitude earthquakes.</p>
<p>Even after a major quake, there’s much seismologists can learn that can hopefully help people prepare for the next one. </p>
<h2>What do we want to know?</h2>
<p>Scientists and policymakers ideally want to forecast the time, place and magnitude of a future earthquake. Knowing that information well in advance, we could issue a region-specific targeted alert, complete with estimates of expected shaking. Such knowledge would allow for the maximum safeguarding of populace and infrastructure. Perfect forecasting would also mean no disastrous <a href="http://www.nytimes.com/2012/10/27/opinion/a-failed-earthquake-prediction-a-crime.html?_r=0">failures-to-predict</a> and no false alarms.</p>
<p>So what can seismologists do to get closer to this goal?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/79991/original/image-20150430-30696-1v9qkjq.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/79991/original/image-20150430-30696-1v9qkjq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/79991/original/image-20150430-30696-1v9qkjq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=375&fit=crop&dpr=1 600w, https://images.theconversation.com/files/79991/original/image-20150430-30696-1v9qkjq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=375&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/79991/original/image-20150430-30696-1v9qkjq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=375&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/79991/original/image-20150430-30696-1v9qkjq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=471&fit=crop&dpr=1 754w, https://images.theconversation.com/files/79991/original/image-20150430-30696-1v9qkjq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=471&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/79991/original/image-20150430-30696-1v9qkjq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=471&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Quakes happen along the edges of the planet’s tectonic plates.</span>
<span class="attribution"><a class="source" href="http://commons.wikimedia.org/wiki/File:Quake_epicenters_1963-98.png">NASA, DTAM project team</a></span>
</figcaption>
</figure>
<h2>It all comes down to plate tectonics</h2>
<p>In seismology, our framework for understanding earthquakes begins with <a href="http://www.livescience.com/37706-what-is-plate-tectonics.html">plate tectonics</a> theory. The Earth’s surface is divided into around 12 major shell-like plates that move relative to one another. Earthquakes happen when the plates rub against each other or collide. We’ve observed that the vast majority of earthquakes occur within the wide (60-600 miles; 100-1,000 km) boundary zones at the edges of the slowly, continuously moving plates. Within these boundaries, plate motions are typically distributed on many active faults that sometimes slip – benignly! – slowly and continuously like the plates. But far more often the plate boundaries stick and are motionless for long periods before suddenly rupturing and producing catastrophic large-magnitude earthquakes.</p>
<p>Given the slow, steady motion of the plates, you might think that earthquakes on plate boundary faults would rupture periodically, say every few decades or centuries, when the stresses that build up on the faults due to the steady motions become greater than the frictional strength holding the fault still. Seismologists have been looking for such nicely behaved faults since the first precision-instrument recordings of earthquakes in 1889, but to no avail. We’ve yet to discover a predictable fault that has a quake right on schedule every 80 years, for example.</p>
<h2>Recording at the surface for hints from within</h2>
<p>We already know a lot about most major faults – where they are, their extents and depths, and at least their recent destructive histories. But there are many crucial things about these faults we don’t understand. The best-studied faults are basically covered with various instruments recording seismic phenomena, and I do mean covered: these observations are made only at the Earth’s surface, or very shallow depths. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/80015/original/image-20150501-30721-2zs6m3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/80015/original/image-20150501-30721-2zs6m3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/80015/original/image-20150501-30721-2zs6m3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/80015/original/image-20150501-30721-2zs6m3.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/80015/original/image-20150501-30721-2zs6m3.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/80015/original/image-20150501-30721-2zs6m3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/80015/original/image-20150501-30721-2zs6m3.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/80015/original/image-20150501-30721-2zs6m3.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Setting up surface sensors to record seismic waves after 2010 earthquake in Chile.</span>
<span class="attribution"><span class="source">Ray Russo</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>We rely on <a href="http://crack.seismo.unr.edu/ftp/pub/louie/class/100/seismic-waves.html">seismic waves</a> generated by earthquakes themselves to characterize the faults and their behavior. These waves of energy spread out from a rupturing fault and are recorded on seismometers and other geophysical instruments. Their characteristics, recognizable to seismologists, tell us about the type of earthquake rupture and the extent of the faulting. But, because these waves travel through complex materials on their way to the Earth’s surface, our ability to ‘see’ details of what happens at depth is inevitably compromised.</p>
<p>Seismic recordings have taught us that major fault zones are complex, typically involving multiple surfaces on which slip can and does occur. These surfaces are usually not continuous, but rather indicate that the major faults are segmented - planes of slightly different orientations juxtaposing <a href="http://nsf.gov/news/news_summ.jsp?cntn_id=110106">potentially very different materials</a>. Different segments of the fault zone can slip apparently independently, although they do influence each other.</p>
<p>Fault surfaces are rough, not smooth, and marked by asperities: sharp bumps, knobs and ridges on the walls of the fault that jab from one side into the other, creating locked points or patches. Stronger patches are more likely to remain locked until the steady plate motions build up enough to break them, while weaker patches slip slowly and steadily. <a href="http://earthquake.usgs.gov/research/parkfield/fluids.php">Groundwater flow</a> may both weaken fault rocks by dissolving minerals, or strengthen a patch of fault through precipitation of new minerals.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/79994/original/image-20150430-30726-1hmm6ue.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/79994/original/image-20150430-30726-1hmm6ue.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/79994/original/image-20150430-30726-1hmm6ue.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/79994/original/image-20150430-30726-1hmm6ue.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/79994/original/image-20150430-30726-1hmm6ue.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/79994/original/image-20150430-30726-1hmm6ue.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=473&fit=crop&dpr=1 754w, https://images.theconversation.com/files/79994/original/image-20150430-30726-1hmm6ue.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=473&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/79994/original/image-20150430-30726-1hmm6ue.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=473&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Japan’s 2011 Tōhoku earthquake registered on seismograms in Hawaii.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/parksjd/7245859020">Joe Parks</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>For every large-magnitude earthquake that occurs on a fault system, thousands or even tens of thousands of little earthquakes will occur. These low-magnitude events can be triggered by small changes in stress on the fault. For example, when seismic waves from a large-magnitude quake somewhere else in the world pass by segments of California’s San Andreas fault, the fault lights up with <a href="http://www.sciencedaily.com/releases/2009/07/090709140817.htm">lots of little tremors</a>. So we infer that many faults are near ‘criticality’ – at least some patches of the fault segments are ready to slip at any time, just waiting for a minuscule amount of stress to be applied.</p>
<p>If the faults are actually moving, just a little bit, essentially all the time, what has to happen for these little motions to coalesce into the big slip over a large area that would be a huge quake? Seismologists have been looking for consistently observed precursory phenomena – some change in fault behavior or structure that always, reliably, occurs before or even during the cascading of little earthquakes into a monster earthquake. So far, we haven’t found it.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/79992/original/image-20150430-30721-bl45jv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/79992/original/image-20150430-30721-bl45jv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/79992/original/image-20150430-30721-bl45jv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=385&fit=crop&dpr=1 600w, https://images.theconversation.com/files/79992/original/image-20150430-30721-bl45jv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=385&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/79992/original/image-20150430-30721-bl45jv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=385&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/79992/original/image-20150430-30721-bl45jv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=483&fit=crop&dpr=1 754w, https://images.theconversation.com/files/79992/original/image-20150430-30721-bl45jv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=483&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/79992/original/image-20150430-30721-bl45jv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=483&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Unloading seismic monitoring equipment in the field.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/ctbto/15642118967">CTBTO</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Lots of science to be done after a big quake</h2>
<p>Ironically, large-magnitude earthquakes like the Nepal event provide some of the most useful information for seismic hazard mitigation: the thousands of aftershocks in the following days and months occur all along the surface of the fault segments that ruptured. Seismologists usually rush to <a href="http://www.earthscope.org/assets/uploads/pages/Wi11_MauleAftershockDeploy.pdf">deploy many temporary seismic stations</a> in the rupture region to record these aftershocks and then locate them with high precision – thus defining the fault’s slip surface accurately.</p>
<p>To do this well, we need to surround the rupture region with sensors that turn shaking due to seismic waves into electrical signals that are then recorded on a weather-proofed computer hard disk. The seismograms they record show the ground moving up and down and side-to-side systematically as the waves travel past the sensor.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/80014/original/image-20150501-30716-1k3ycn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/80014/original/image-20150501-30716-1k3ycn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/80014/original/image-20150501-30716-1k3ycn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=373&fit=crop&dpr=1 600w, https://images.theconversation.com/files/80014/original/image-20150501-30716-1k3ycn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=373&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/80014/original/image-20150501-30716-1k3ycn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=373&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/80014/original/image-20150501-30716-1k3ycn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=468&fit=crop&dpr=1 754w, https://images.theconversation.com/files/80014/original/image-20150501-30716-1k3ycn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=468&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/80014/original/image-20150501-30716-1k3ycn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=468&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Example of a seismic microzonation map for the city of Bangkok.</span>
<span class="attribution"><a class="source" href="http://en.wikipedia.org/wiki/File:Bangkok_microzonation_map.jpg">Tuladhar, R., Yamazaki, F., Warnitchai, P & Saita, J., Seismic Microzonation of the Greater Bangkok area using Microtremor Observations, Earthquake Engineering and Structural Dynamics,v33, 2004: 211-225</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The aftershock team’s work affords us an accurate measure of these parameters. Then we can make a firm estimate of the largest magnitude earthquake a particular cascading sequence of rupturing fault segments can produce. The upper magnitude limit for the region can then be used to estimate the maximum expected shaking, and, in combination with studies of substrate materials, <a href="http://earthquake.usgs.gov/hazards/designmaps/">expected hazard maps</a> can be produced, building codes updated based on realistic expectations, and civil defense planning focused to mitigate specific disaster scenarios.</p>
<h2>How to protect against future quake disasters?</h2>
<p>The <a href="http://earthquake.usgs.gov/earthquakes/eventpage/us20002926#general_summary">Nepal earthquake</a> was long expected. A <a href="http://www.rediff.com/news/report/nepal-earthquake-is-an-eerie-reminder-of-1934-tragedy/20150425.htm">predecessor event in 1934</a> ruptured an even greater area, yielding a higher magnitude quake. And if earthquake preparedness there received less-than effective attention given this clear warning, imagine how much more difficult it is to motivate preparation in places that are susceptible to huge earthquakes, but whose most recent big quake occurred long before any of us were born, even before written history…. The past is never truly past, indeed!</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/79993/original/image-20150430-30709-z5suvr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/79993/original/image-20150430-30709-z5suvr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/79993/original/image-20150430-30709-z5suvr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/79993/original/image-20150430-30709-z5suvr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/79993/original/image-20150430-30709-z5suvr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/79993/original/image-20150430-30709-z5suvr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/79993/original/image-20150430-30709-z5suvr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/79993/original/image-20150430-30709-z5suvr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Nepal’s earthquake caused countless buildings to crumble.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/unitednationsdevelopmentprogramme/17250166966">United Nations Development Programme</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>Globally, we need a program of identification and characterization of potentially hazardous faults in urban areas. From those studies, site-specific expected seismic shaking maps can be developed and construction codes and engineering design specifications for infrastructure enacted, mitigating hazard to new and future construction.</p>
<p>Then urban political leaders and civil defense agencies must collaborate to lead local populations in an open and honest dialog to identify both irreplaceable cultural heritage, and also infrastructure that must survive natural disasters intact in order to prevent an earthquake from triggering a series of consequent catastrophes – fires, water and food shortages and disease outbreaks. These structures should be retrofitted to survive the predicted shaking from the maximum expected magnitude earthquake for the given area. A number of different mechanisms to pay for this costly preventive engineering are almost certainly needed, tailored to local conditions.</p>
<p>It’s clear the Earth has moved before and will move again, but will we move to do what’s necessary to mitigate preventable disasters?</p><img src="https://counter.theconversation.com/content/34472/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ray Russo receives funding from the US National Science Foundation.</span></em></p>For seismologists, there’s much to be learned after a major earthquake, as aftershocks help them map out the fault with high precision. More data now can prepare a region for its next big one.Ray Russo, Associate Professor of Geophysics, University of FloridaLicensed as Creative Commons – attribution, no derivatives.