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

2004年12月26日，超过25万人丧生，这表明印度洋地区易受毁灭性地震和海啸的影响。根据初步的实地调查，现在看来，在苏门答腊俯冲带最北端的苏门答腊沿海平原上新发现的埋藏土壤含有2004年安达曼-亚齐地震的全新世（1万年前到现在）前身的证据。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科学研究所和地质技术研究中心的一个研究小组正在研究这些矿床，以便了解和记录苏门答腊最北端的巽他巨型逆冲断层的全新世地震行为。通过整合古地震学、大地测量学、地质年代学和利用微体化石重建古环境，该小组将建立一个大约5000年前苏门答腊北方近海苏门答腊俯冲带最北端的俯冲带年代学。结果将记录地震引起的快速沉降和海平面的逐渐变化，这些变化与同震陆地平面变化无关，也是随后的变化。记录的相对海平面变化将有助于限制在主俯冲带地震之前，期间和之后滑动的范围和幅度。一个跨越至少三个或四个地震周期的俯冲带地震的长期记录将提供对地震和海啸之间平均时间的现实估计，类似于2004年12月袭击北方苏门答腊西海岸的地震和随后发生的海啸。初步工作表明，古地震记录是目前在沿海湿地地层和湿地沉积物中含有可测年的材料和丰富的微体化石，将允许重建的时间和幅度的垂直陆地水平变化在海岸之前，伴随着和以下俯冲带地震。有文字记载的历史未能对2004年12月26日巽他巨型逆冲断层地震及其引发的海啸的可能性提出预警。根据初步工作，研究小组已经确定了热带环境，那里最有可能形成和维持以前的巨型逆冲断层地震记录。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之间平均时间的现实估计，类似于2004年的地震和随后的海啸。该项目的成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一起传播。这些结果将确定，地震和海啸是经常发生的事件，应加以预测，并需要灾害规划。

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.