Collaborative Research: A Paleoseismic Record of Great Earthquakes on the Sunda Subduction Megathrust, Northern Sumatra

2004年12月26日，25多万人丧生，这表明印度洋地区对破坏性地震和海啸的易感性。根据初步的田野调查，现在看来，在苏门答腊俯冲带最北端的苏门答腊海岸平原上新发现的埋藏土壤包含了2004年安达曼-亚齐地震之前的全新世（距今1万年）的证据。来自中央华盛顿大学、洪堡州立大学、宾夕法尼亚大学和印度尼西亚地质技术科学研究中心的一个研究小组正在研究这些沉积物，以了解和记录苏门答腊岛最北端巽他巨型逆冲构造的全新世地震行为。通过整合古地震学、大地测量学、地质年代学和使用微化石重建的古环境，该团队将建立一个俯冲带的最北端的过去，可以追溯到大约5000年前的苏门答腊北部近海的俯冲带。结果将记录地震引起的快速沉降和海平面的逐渐变化，这些变化发生在同震陆地水平变化之前和之后。记录的相对海平面变化将有助于限制主俯冲带地震发生前、发生中和发生后的滑动范围和幅度。对至少跨越三到四个地震周期的俯冲带地震的长期记录将为地震和海啸之间的平均时间提供现实的估计，类似于2004年12月袭击苏门答腊岛北部西海岸的地震和随之而来的海啸。初步研究表明，沿海湿地地层中存在古地震记录，湿地沉积物中含有可测定数据的物质和丰富的微化石，这将允许重建海岸垂直陆地水平变化的时间和幅度，这些变化发生在俯冲带地震之前、伴随和之后。有文字记载的历史并没有对2004年12月26日可能发生的巽他大地震及其引发的海啸做出预警。在初步工作的基础上，研究小组已经确定了热带环境，在那里，前大型逆冲地震的记录最有可能形成并持续下去。这些沉积物将产生数千年来俯冲带地震的长期记录，并将提供地震和海啸（类似于2004年的地震和随后的海啸）之间平均时间的现实估计。该项目的结果将在苏门答腊沿海社区内传播，并与苏门答腊和国家政府机构传播。这些结果将证明，地震和海啸是经常发生的事件，应该加以预测，需要进行灾害规划。

The loss of more than a quarter million lives on December 26, 2004 revealed the susceptibility of the Indian Ocean region to devastating earthquakes and tsunamis. Based upon preliminary fieldwork it now appears that newly discovered buried soils on the Sumatran coastal plain of northernmost part of the Sumatran subduction zone contain evidence for Holocene (10,000 years ago to the present) predecessors to the 2004 Andaman-Aceh earthquake. A research team from Central Washington University, Humboldt State University, the University of Pennsylvania, and the Indonesian Institute of Sciences and Research Center for Geotechnology are studying these deposits in order to understand and chronicle the Holocene seismic behavior of the Sunda megathrust of northernmost Sumatra. Through integration of paleoseismology, geodesy, geochronology, and paleoenvironmental reconstruction using microfossils, the team will establish a subduction zone chronology for the northernmost past of the Sumatran subduction zone offshore of northern Sumatra going back approximately five thousand years. The results will chronicle earthquake-induced rapid subsidence and gradual sea-level changes precursory to, and subsequent to, the coseismic land level changes. The documented relative sea-level changes will help constrain the extent and magnitude of slip before, during and after the main subduction zone earthquake. A long-term record of subduction zone earthquakes that spans at least three or four earthquake cycles will provide realistic estimates of the average time between earthquakes and tsunamis similar to the earthquake and ensuing tsunami that struck the west coast of northern Sumatra in December 2004. Preliminary work demonstrates that a paleoearthquake record is present in coastal wetland stratigraphy and that wetland sediment contains both datable material and abundant microfossils that will permit reconstruction of the timing and magnitude of vertical land level changes at the coast that precede, accompany and follow subduction zone earthquakes. Written history had failed to forewarn of the possibility of a giant Sunda megathrust earthquake and the resulting tsunami of December 26, 2004. Based on preliminary work, the research team has identified tropical environments where the record of former megathrust earthquakes is most likely to form and endure. These deposits will yield a long-term record of subduction zone earthquakes over thousands of years and will provide realistic estimates of the average time between earthquakes and tsunamis such similar to the 2004 earthquake and ensuing tsunami. Results from this project will be disseminated within the Sumatran coastal communities and with Sumatran and national governmental agencies. These results will establish that earthquake and tsunami are recurrent events that should be anticipated and that require disaster planning.