Collaborative Research: High-Precision Teleseismic Relocation and Tomography for the M 9 and M 8.7 Sumatra Great Earthquake Sequences

合作研究：苏门答腊岛9级和8.7级大地震的高精度远震重定位和层析成像

• 批准号: 0608739
• 负责人: Felix Waldhauser
• 金额: --
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-07-01 至 2010-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0608739&HistoricalAwards=false
• 关键词: Collaborative; Research; Precision; Teleseismic; Relocation

The seismic and tsunami hazard posed by great subduction zone earthquakes has long been recognized, but in light of the December 26, 2004 Mw 9+ Sumatra-Andaman Islands earthquake, the resulting tsunami, infrastructure damage and huge loss of life, it is clear that the danger posed by such events remains underestimated. The Sumatra great earthquake is one of the four largest events in the instrumental record, comparable in many respects to the 1960 Mw 9.5 Chilean and 1964 Mw 9.2 Alaska subduction megathrust events that generated significant damage and tsumani within the Pacific ocean basin. The Sumatra-Andaman Islands event triggered a second great earthquake, the March 28, 2005 Mw 8.7 Nias event, directly to the south, increasing concerns about the occurrence of a third great earthquake offshore southern Sumatra in the near-term. This study consists of a series of high-precision earthquake relocation of the 2004 and 2005 Sumatra aftershock sequences and prior regional seismicity and computation of compressional and shear seismic wave speeds in three-dimensions for the Sumatra region in order to better constrain how thermal, mechanical, compositional, hydrological, and rupture processes interact along subduction megathrusts during great earthquakes. The 2004 and 2005 main shock and aftershock sequences generated over 5000 earthquakes recorded globally by seismic networks along 1700 km of subduction system. In the Sumatra region, however, the seismogenic portion of the subduction megathrust lies primarily within an oceanic environment, which ultimately limits the amount and coverage of local and regional seismic data that will become available, and emphasizes the need for state-of-the-art analysis of the available global data. The increased precision earthquake catalog is used to refine subduction zone geometry and to explore spatio-temporal variability within and between the aftershock series. Comparisons between aftershocks and prior regional seismicity provide insight into processes within the subduction zone leading up to these great earthquakes, while comparisons between compressional and shear wave speed models and regional seismicity patterns can be related to variations in rupture behavior along the subduction megathrust. The study builds over three stages: 1) probabilistic phase re-determination, waveform cross-correlation of phases to reduce picking error, and single-event earthquake relocations using the Engdahl, van der Hilst, and Buland method, 2) high-precision relative earthquake locations using teleseismic double-difference methods, and 3) inversion for regional compressional and shear wave speed models in three dimensions using teleseismic DD tomography methods. Among the broader impacts are: 1) The methods developed significantly advance the use of global catalog and waveform data to study regional-scale problems where high spatial density local seismometer deployments are not feasible, and all techniques are shared with the public; 2) Data analysis and interpretation involves undergraduate, graduate, and young investigator collaboration with well-established experts in the fields of earthquake location and tomography; and 3) The project involves five institutions, including the Institut Teknologi Bandung, and strengthens ties with the scientific community in Indonesia.

人们早就认识到俯冲带大地震造成的地震和海啸危害，但鉴于2004年12月26日苏门答腊-安达曼群岛发生的9级以上地震，由此引发的海啸、基础设施破坏和巨大的生命损失，很明显，这类事件造成的危险仍然被低估了。苏门答腊大地震是仪器记录的四大地震之一，在许多方面可与1960年智利9.5兆瓦和1964年阿拉斯加9.2兆瓦的俯冲大逆冲事件相媲美，后者在太平洋盆地内造成了严重的破坏和海啸。苏门答腊-安达曼群岛的地震引发了第二次大地震，即2005年3月28日发生在正南的8.7级尼亚斯地震，这增加了人们对近期苏门答腊南部近海发生第三次大地震的担忧。本研究通过对2004年和2005年苏门答腊岛余震序列和先前区域地震活动性进行一系列高精度地震重新定位，并在三维上计算苏门答腊岛地区的纵波和横波速度，以便更好地约束大地震期间沿俯冲巨型逆冲断层的热、力学、成分、水文和破裂过程如何相互作用。2004年和2005年的主震和余震序列产生了全球1700公里俯冲系统沿线地震台网记录的5000多次地震。然而，在苏门答腊地区，俯冲巨型逆冲构造的发震部分主要位于海洋环境中，这最终限制了当地和区域地震数据的数量和覆盖范围，并强调需要对现有的全球数据进行最先进的分析。提高精度的地震目录用于细化俯冲带的几何形状，并探索余震系列内部和之间的时空变异性。对比余震和之前的区域地震活动，可以深入了解导致这些大地震的俯冲带内部过程，而对比纵波和横波速度模型和区域地震活动模式，可以与俯冲大逆冲断层破裂行为的变化有关。研究分为三个阶段：1)概率相位重新确定，相位波形相互关联以减少采集误差，使用Engdahl， van der Hilst和Buland方法进行单事件地震重新定位；2)使用远震双差方法进行高精度相对地震定位；3)使用远震DD层析成像方法进行区域纵波和横波速度模型的三维反演。主要影响有：1)所开发的方法显著促进了利用全球目录和波形数据来研究区域尺度问题，而在这些问题上，高空间密度的局地地震仪部署是不可实现的，并且所有技术都与公众共享；2)数据分析和解释涉及本科生、研究生和青年研究者与地震定位和断层成像领域的知名专家合作；3)该项目涉及五个机构，包括万隆技术研究所，并加强了与印度尼西亚科学界的联系。