Evaluation of Historical Earthquake Interaction and Seismic Risk to Western Sumatra

2004年12月26日，苏门答腊安达曼大地震使巽他逆冲断层断裂，长度超过1200公里，造成9.3级地震和大规模海啸，摧毁了整个环印度洋海岸线。超过25万人死亡。地震不是孤立发生的，而是一次地震使其周围的地壳变形，并将应力转移到其他结构上，这些结构也可能产生其他地震，即所谓的触发地震。在过去十年左右的时间里，科学家们试图了解这种效应，并开发了计算地壳中这些相互作用应力的数学工具。这项工作导致的想法，如果相互作用的应力可以在地震后立即计算，可能会产生其他事件的结构可能被识别，从而定位特别高的地震危险的地区。在苏门答腊-安达曼地震之后，阿尔斯特大学物理学研究小组通过指出在苏门答腊以西的锡默卢岛和尼亚斯岛下发生另一次大地震（即M>8）的风险增加来说明这种方法的有用性。虽然这项工作清楚地说明了这项技术的力量，但不幸的是，计算出的应力与随后的地震之间没有一对一的映射。因此，虽然我们可以说另一场地震可能发生在哪里，但我们不能说何时发生，甚至可能性有多大。如果我们要有信心地和一贯地以实际的方式使用相互作用应力技术，那么做更多的工作是非常重要的。另一个关键而密切相关的问题是：我们试图预测什么样的地震？虽然有些科学家认为大地震会在同一个地方发生，但震级或多或少相同，其他人则指出这一观点的重大错误。大地震有时会重叠，发生在不同的地方，联合收割机组合成更大的地震或打破一个以上的断层。在这个项目中，这个团队汇集了来自阿尔斯特和爱丁堡大学以及罗马国家地球物理和火山学研究所的科学家，他们将研究相互作用应力的想法有多好，不是通过展望未来，而是通过展望过去。由于科学家们20多年来的共同努力，地球上很少有地方对过去的大地震（M>8）活动有更好的了解。我们确信，我们知道自1600年以来发生在那里的所有地震（M>6）的位置和大致规模。我们也知道很多关于板块聚合--地震产生的驱动力。在这个项目中，我们将把这些信息放在一个复杂的数值模拟中，以重建过去400年来西苏门答腊地区的整个应力场。由此产生的三维应力历史将使我们能够看到相互作用应力的想法是否可以用来解释过去400年的地震;这将有助于我们了解接下来可能发生的事情。此外，我们还将研究最近较小地震的记录，看看我们是否可以利用这些记录来告诉我们大地震简单复发行为的可靠性。这个问题很复杂，需要非常仔细地应用统计技术，以确保我们得出正确的结论。我们将在项目期间开发其中的许多功能。苏门答腊西部目前是世界上地震风险最高的地区之一。印度洋沿岸的居民，特别是苏门答腊岛西海岸的居民，生活在另一场大地震的威胁之下，这场地震有可能造成与节礼日地震同等规模的死亡。这个项目不会阻止地震，但它将有助于科学知识的主体，最终将有助于人们做好准备。

On 26 December 2004 the great Sumatra Andaman Earthquake ruptured the Sunda megathrust for a length of more than 1200km resulting in a magnitude 9.3 earthquake and a massive tsunami which devastated the entire circum-Indian ocean coastline. Over 250000 people died. Earthquakes do not occur in isolation but one earthquake deforms the earth's crust around it and transfers stress onto other structures which may also generate other, so called triggered earthquakes. Over the last ten years or so, scientists have tried to understand this effect and have developed mathematical tools for the calculation of these interaction stresses in the crust. This work has lead to the idea that if the interaction stresses could be calculated immediately after an earthquake, the structures which would be likely to produce other events might be identified, thus locating areas of particularly high seismic hazard. Following the Sumatra-Andaman earthquake, the University of Ulster geophysics research group illustrated the usefulness of this method by pointing out the increase risk of another great (ie M>8) earthquake under the Islands of Simeulue and Nias to the west of Sumatra. The forecast event occurred (M8.7) 11 days after their paper was published in Nature While this work clearly illustrated the power of the technique there is, unfortunately not one-to-one mapping between the calculated stresses and the following earthquakes. So, while we can say where another earthquake is likely we cannot say when, or even how likely. It is of great importance that more work is done if we are to be able confidently and consistently to use the interaction stress technique in a practical way. Another crucial and closely linked question is: what earthquake are we trying to forecast? While some scientists believe that big earthquakes recur with more or less the same magnitude in more or less the same place, others point out significant failures in this idea. Big earthquakes sometimes overlap, occur in different places, combine into even bigger earthquakes or break more than one fault. In this project, the team, which brings together scientists from the universities of Ulster and Edinburgh as well as from the National Institute for Geophysics and Vulcanology in Rome, will examine how good the interaction stress idea is, not by looking into the future, but by looking into the past. Due to the concerted effort of scientists for over 20 years, there are few places on earth for which we have a better picture of past big (M>8) earthquake activity. We are confident that we know the locations and approximate sizes of all earthquakes (M>6) which have occurred there since about 1600. We also know a lot about plate convergence - the driving force for earthquake generation. In this project we will put this information together in a complex numerical simulation to reconstruct the entire stress field in the western Sumatran region for the last 400 years. The resulting 3D stress history will allow us to see if the interaction stress idea could have been used to explain the last 400 years of earthquakes; this will help us to understand what is likely to happen next. In addition we will look at the recent records of smaller earthquakes and see if we can use these to tell us about the dependability of the simple recurrence behaviour for the big ones. This problem is complex and requires very careful application of statistical techniques to be sure we reach the right conclusions. We will develop many of these during the project. Western Sumatra is currently one of highest earthquake risk areas in the world. Coastal populations around the Indian ocean, and on the western coast of Sumatra in particular live with the threat of another great earthquake which has the potential to kill on the same scale as the boxing day event. This project will not stop the earthquake but it will contribute to a body of scientific knowledge which will ultimately help to prepare people for it.