Subduction zone segmentation and controls on earthquake rupture: The 2004 and 2005 Sumatra earthquakes

俯冲带分割和地震破裂控制：2004年和2005年苏门答腊岛地震

• 批准号: NE/D003431/1
• 负责人: Timothy Henstock
• 金额: $ 27.23万
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2006
• 资助国家: 英国
• 起止时间: 2006 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FD003431%2F1
• 关键词: Subduction; zone; segmentation; controls; earthquake

The Sumatran earthquake of December 26th 2004 was the second-largest earthquake on record. The growing concentrations of population in regions prone to great earthquakes makes it a matter of urgency to study the processes that control these earthquakes. The Sumatran earthquake is the first to which modern geophysical tools can be applied, so offers a unique opportunity for such study. Most great earthquakes (magnitude 8 and larger) take place where two plates converge; such regions lie mostly under water, which makes them difficult to investigate, and which means that the hazard of tsunamis is added to the dangers of ground shaking. In the December 26th 2004 earthquake, the Australian and Eurasian plates slipped towards each other by up to 25 metres, on a fault that runs for 1200 km along the earth's surface. An obvious question is: Why was this earthquake so large? But perhaps the question should be: Why wasn't this earthquake larger? because, in March 2005 an adjacent 400 km of the plate boundary slipped in a second huge earthquake. All plate boundaries are divided into segments - pieces of fault that are distinct from one another, either separated by gaps or with different orientations. The boundaries between segments provide barriers that limit how far an earthquake can spread. A large earthquake may rupture a whole segment of plate boundary, but a great earthquake usually ruptures more than one segment at once. However, we do not know what determines whether an earthquake stays within one segment of plate boundary (and remains relatively small), or jumps across barriers between segments (to become a great earthquake). The Sumatran earthquakes give a unique framework to attack this problem. Detailed analyses of the seismic waves radiated by the Sumatran earthquakes give accurate locations for the barriers controlling the sizes of the earthquakes. The December 2004 earthquake started close to Banda Aceh and spread almost entirely northwards. Although 25 metres of slip occurred near the southern end of the rupture, almost no slip spread to the south; clearly, an important barrier here prevented the earthquake spreading to the next fault segment. In March 2005 another great earthquake occurred within this next segment, and spread southwards until it was stopped by a barrier at its southern end. We will conduct detailed geophysical surveys of the plate boundary to determine the nature of these two barriers. Large-scale (1-20km resolution) images of the plate boundary will be obtained in a combined land-sea experiment using air-gun explosions to bounce seismic waves off structures inside the plate boundary. In a longer-term experiment, seismometers left on land and on the sea-bed for several months will pick up the seismic signals from distant earthquakes. These waves, travelling upwards through the earth to the array of seismometers, can be used (in a fashion similar to CAT scanning) to form 3-dimensional images of the deeper parts of the crust and upper mantle. At the same time, new techniques will be developed to give more precise pictures of the distribution of slip in the two earthquakes, in order to link the static structure of the plate boundary to the dynamics of the earthquakes. Cores from the seabed will show when large earthquakes have occurred on these faults in the past, and whether the segmentation seen in 2004-5 was similar in the past events. In addition, we will collect evidence for the ways in which fault slip affects the seabed and generates a tsunami. The results will be significant both locally and globally. It is important to compare the barrier between the 2004 and 2005 earthquakes with the barrier at the south of the 2005 earthquake, because the plate boundary immediately to the south slipped in 1833, causing a devastating tsunami. More generally, the results will have implications for other convergent boundaries, such as those beneath Japan, and on land associated with the Himalayas.

2004年12月26日的苏门答腊岛地震是有记录以来第二大地震。人口日益集中在易发生大地震的地区，这使得研究控制这些地震的过程成为当务之急。苏门答腊岛地震是第一次可以应用现代地球物理工具的地震，因此为此类研究提供了一个独特的机会。大多数大地震(8级或更大)发生在两个板块交汇的地方；这些地区大多位于水下，这使得它们很难调查，这意味着海啸的危险增加了地面震动的危险。在2004年12月26日的地震中，澳大利亚和欧亚板块在一条沿地球表面绵延1200公里的断层上向对方滑动了25米。一个显而易见的问题是：为什么这场地震会如此强烈？但或许问题应该是：为什么这次地震的震级不大？因为，2005年3月，邻近的400公里板块边界在第二次大地震中滑动。所有板块边界都被划分成不同的断层段，这些断层段彼此不同，要么被缝隙隔开，要么具有不同的方向。地段之间的边界提供了障碍，限制了地震的传播距离。一次大地震可能会使一整段板块边界破裂，但一次大地震通常会同时破裂不止一段。然而，我们不知道是什么决定了地震是停留在板块边界的某一段内(并且保持相对较小的规模)，还是跨越板块边界之间的障碍(成为大地震)。苏门答腊岛地震为解决这一问题提供了一个独特的框架。对苏门答腊岛地震辐射的地震波的详细分析为控制地震大小的屏障提供了准确的位置。2004年12月的地震开始于班达亚齐附近，几乎完全向北蔓延。尽管断裂南端附近发生了25米的滑动，但几乎没有滑动向南扩散；显然，这里有一个重要的屏障阻止了地震蔓延到下一个断层段。2005年3月，下一段又发生了一次大地震，并向南蔓延，直到被南端的障碍物阻止。我们将对板块边界进行详细的地球物理测量，以确定这两个障碍的性质。在陆地-海洋联合实验中，将使用气枪爆炸将地震波从板块边界内的结构上反弹，从而获得大尺度(1-20公里分辨率)的板块边界图像。在一项更长期的实验中，放置在陆地和海床上几个月的地震仪将捕捉到来自遥远地震的地震信号。这些通过地球向上传播到地震仪阵列的波，可以用来(以一种类似于CAT扫描的方式)形成地壳和上地幔更深部分的三维图像。同时，将开发新的技术，以提供两次地震中更精确的滑移分布图像，以便将板块边界的静态结构与地震的动态联系起来。来自海底的岩芯将显示这些断层过去发生大地震的时间，以及2004-2005年看到的分段是否与过去的事件相似。此外，我们还将收集有关断层滑动影响海床并引发海啸的证据。无论是在当地还是在全球，结果都将是重大的。重要的是要将2004年和2005年地震期间的屏障与2005年地震南边的屏障进行比较，因为紧邻南方的板块边界在1833年滑动，造成了毁灭性的海啸。更广泛地说，这一结果将对其他汇聚的边界产生影响，例如日本下方的边界，以及与喜马拉雅山脉相关的土地上的边界。

项目成果

Exploring Structural Controls on Sumatran Earthquakes

探索苏门答腊地震的结构控制

• DOI: 10.1029/2010eo440002
• 发表时间: 2011
• 期刊: Eos, Transactions American Geophysical Union
• 作者: Henstock T

Aseismic zone and earthquake segmentation associated with a deep subducted seamount in Sumatra

• DOI: 10.1038/ngeo1119
• 发表时间: 2011-05
• 期刊: Nature Geoscience
• 影响因子: 18.3
• 作者: Satish C. Singh;N. Hananto;Maruf Mukti;David P. Robinson;Shamita Das;A. Chauhan;H. Carton;B. Gratacos;Stephan Midnet;Y. Djajadihardja;H. Harjono

Earthquake fault superhighways

地震断层高速公路

• DOI: 10.1016/j.tecto.2010.01.010
• 发表时间: 2010
• 期刊: Tectonophysics
• 影响因子: 2.9
• 作者: Robinson D