Sumatran Stress History for Forecasting Near-Future Tsunami Innudation

自2004年12月以来，在一系列大俯冲地震中，舜他巨型逆冲断裂被撕裂，造成约250000人死亡，这极大地说明了俯冲带地震的破坏力，并激发了新的研究活动来了解它们。这一序列提供了在地震科学方面取得根本性进展的独特机会，原因有三：1.这些大地震被记录得前所未有地清晰。在十多年的时间里部署的仪器不仅产生了地震期间和之后滑动的详细图像，而且还产生了界面耦合的详细分布图-其中应变积累到接近断点的位置，断层在哪里无害地滑动，并帮助解释了它们在哪里破裂。2.苏门答腊岛海岸和近海岛屿在一个主要板块边界上独一无二地被珊瑚微型环礁殖民，它们的生长习性记录了可追溯到700年前的形变的垂直分量。这为理解几个地震周期的形变提供了可能性--目前在任何其他俯冲带上都是不可能的。3.在目前的NERC项目中，已经开发了一种技术--蒙特卡罗滑动估计(MCSE)，该技术基于该珊瑚大地测量产生对巨型逆冲上的地震间载荷和滑动的高分辨率概率估计。(1797年(M8.8级)和1833年(M9.0级)地震的MCSE显示了200年前地震中现代滑动耦合的显著控制，定量地说明苏门答腊岛的凹凸体是长期存在的。)在受珊瑚大地测量约束的历史地震中，板块耦合的分布与已知的收敛和应变释放速率相结合，试图解释最近的地震。虽然2004年和2005年地震的特征很好地符合一个相对简单的应变积累和释放模型，但2007年的地震集中在遥远的南方，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，但断裂带预应力和地震间隔期可能的非地震松弛时期的不完整模型在图中留下了重要的空白。这个项目将有助于填补这些空白。MCSE与精心构建的覆盖从赤道到4S的巨型逆冲的珊瑚位移数据库相结合，将产生700年来应变积累和释放的记录。对于地震间加载的每一段时间，可能包含非地震滑动的片段，对于每一次地震，巨型断裂上的滑动或载荷都将与模型中明确的不确定性分布一起模拟。其结果将是一部700年来断层压力积累和释放的电影。目前，地球上没有其他任何地方可以进行这样的重建。以前从未有人如此系统地尝试过这一点。将近期地震的滑移分布与700年的应力史进行详细的对比，将为理解破裂的形核、扩展和终止机制提供难得的机会。我们不仅将有助于对地震成因的科学理解，而且这项研究还将绘制明打威群岛下一次地震的滑动概率地图，预计下一次地震将立即破裂巨型断裂的西比鲁特段，并可能引发毁灭性的海啸。这张概率图将被用来生成一系列可能的地震模型，这些模型将推动高分辨率水深测量和数字高程模型上的海啸模拟，从而产生对不久的将来地震可能淹没的统计估计。应当地非政府组织Kogami的要求，他们正在努力教育苏门答腊岛海岸的高危社区，选定的模拟将被开发成洪水动画，用于这项教育工作。

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.