Sumatran Stress History for Forecasting Near-Future Tsunami Innudation

自2004年12月以来，超过2000公里的Sunda巨型逆冲断层在一系列巨大的俯冲地震中被撕开，估计造成25万人死亡，这极大地说明了俯冲带地震的破坏力，并刺激了新的研究活动来了解它们。这一序列提供了一个独特的机会，使地震科学的根本进步有三个原因：1。这些大地震被前所未有的清晰记录下来。在十多年的时间里部署的仪器不仅提供了地震期间和之后滑动的详细图片，而且还提供了界面耦合分布的详细地图-应变正在接近断裂点，断层正在无害地滑动，并有助于解释为什么它们在那里破裂。2.独特的主要板块边界，苏门答腊海岸和近海岛屿殖民与珊瑚微环礁的生长习性记录的变形延伸到700年的垂直分量。这些提供了理解几个地震周期的变形的可能性-目前在任何其他俯冲带都不可能。3.在当前NERC项目中，开发了一种技术，即蒙特-卡罗滑动估计（MCSE），该技术基于珊瑚大地测量学对巨型逆冲断层的震间载荷和滑动进行高分辨率概率估计。(MCSE 1797年（M8.8）和1833年（M9.0）地震显示了对现今耦合的显著控制，对200年前地震的滑动进行了定量说明，Summerian凸体是长寿的。）板块耦合的分布与珊瑚大地测量学约束的历史地震中已知的会聚速率和应变释放速率一起被联合收割机结合起来，试图解释最近的地震。虽然2004年和2005年地震的特征与相对简单的应变积累和释放模型非常吻合，但2007年的地震在遥远的南方成核，并没有在足够大的区域内释放预期的能量。耦合的分布解释了许多观测结果，但断层带预应力和地震间地震松弛的可能时期的不完整模型在图片中留下了重要的空白。该项目将有助于填补这些空白。MCSE与精心构建的珊瑚位移数据库相结合，涵盖了从赤道到4S的巨型逆冲断层，将产生700年的应变积累和释放记录。对于每一个震间加载周期（可能包含抗震滑动事件），以及对于每一次地震，将对巨型逆冲断层上的滑动或载荷进行建模，并在模型中明确分布不确定性。结果将是一部700年断层应力积累和释放的电影。目前，地球上没有其他地方可以进行这样的重建。以前从未如此系统地尝试过。将最近地震中的滑移分布与这700年的应力历史进行详细比较，将为理解破裂成核、传播和终止的机制提供一个独特的机会。我们不仅将有助于对地震成因的科学理解，而且这项研究将绘制出下一次明打威群岛地震发生滑动的可能性地图，预计下一次明打威群岛地震将使大逆冲断层的西比路段立即破裂，并可能产生毁灭性的海啸。这一概率图将用于生成一系列可能的地震模型，这些模型将推动高分辨率测深和数字高程模型的海啸模拟，从而对近期地震可能造成的淹没作出统计估计。应当地一个致力于教育苏门答腊海岸风险社区的非政府组织KOGAMI的请求，将选定模拟制作成洪水动画，供教育工作使用。

Since December 2004 over 2000 km of the Sunda megathrust fault has been ripped open in a sequence of great subduction earthquakes killing an estimated 250000, dramatically illustrating the destructive power of subduction zone earthquakes and stimulating renewed research activity to understand them. This sequence provides a unique opportunity to make a fundamental advance in earthquake science for three reasons: 1. These great earthquakes have been recorded with unprecedented clarity. Instruments deployed over a period of more than a decade have not only produced a detailed picture of the slip during and after the shocks but have produced detailed maps of the distribution of interface coupling - where strain is building up to near breaking point and where the fault is slipping harmlessly and helping to explain why they ruptured where they did. 2. Uniquely on a major plate boundary, the Sumatra coast and offshore islands are colonised with coral microatolls whose growth habit records the vertical component of deformation extending back up to 700 years. These give the possibility of understanding the deformation over several seismic cycles - currently impossible on any other subduction zone. 3. In a current NERC project a technique, Monte-Carlo Slip Estimation (MCSE), has been developed which produces high-resolution probabilistic estimates of interseismic loading and slip on the megathrust based on this coral geodesy. (MCSE for the 1797 (M8.8) and 1833 (M9.0) earthquakes show remarkable control of present-day coupling on slip in 200 year old earthquakes quantitatively illustrate that Sumatran asperities are long-lived.) The distribution of plate coupling together with known rates of convergence and strain release in historical earthquakes constrained by the coral geodesy have been combine to attempt to explain the recent earthquakes. While features of the 2004 and 2005 earthquakes conform well to a relatively simple model of strain accumulation and release, the 2007 event nucleates to far south and does not release the expected energy over a big enough region. Distributions of coupling explain many observations, but an incomplete model of the fault zone pre-stress and probable periods of aseismic relaxation in the interseismic periods has left vital gaps in the picture. This project will help to fill these gaps. MCSE, combined with a carefully constructed database of coral displacements covering the megathrust from the equator to 4S, will produce a 700 year record of strain accumulation and release. For every period of interseismic loading, possibly containing episodes of aseismic slip, and for every earthquake, the slip, or load, on the megathrust will be modelled together with a clear distribution of uncertainty in the model. The result will be a movie of 700 years of on-fault stress accumulation and release. Nowhere else on the planet is such a reconstruction currently possible. Never before has it been so systematically attempted. Detailed comparison of the slip distributions in the recent earthquakes with this 700 year stressing history will provide a unique opportunity to understand the mechanisms for rupture nucleation, propagation and termination. Not only will we contribute to the scientific understanding of seismogenesis but the study will produce a map of the probability of slip on the next Mentawai Islands earthquake which is expect to rupture the Siberut segment of the megathrust imminently and potentially generate a devastating tsunami. This probability map will be used to generate a series of possible earthquake models which will drive tsunami simulations over high-resolution bathymetric and digital elevation models producing statistical estimates of likely inundation from a near-future earthquake. At the request of KOGAMI, a local NGO who are working to educate at-risk communities on the Sumatran coast, selected simulations will be developed into inundation animations for use in this educational work.