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: 0609613
• 负责人: E.Robert Engdahl
• 金额: $ 5.97万
• 依托单位: University of Colorado at Boulder
• 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 2008-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0609613&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.

人们早已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日发生的Mw 9+苏门答腊岛安达曼群岛地震以及由此引发的海啸、基础设施损坏和巨大的生命损失，很明显此类事件造成的危险仍然被低估。苏门答腊大地震是仪器记录中四大事件之一，在许多方面可与 1960 年智利 Mw 9.5 和 1964 年阿拉斯加 Mw 9.2 俯冲巨型逆冲事件相媲美，这些事件在太平洋盆地内造成了严重破坏和海啸。苏门答腊-安达曼群岛事件引发了第二次大地震，即 2005 年 3 月 28 日发生的兆瓦级 8.7 尼亚斯事件，直接发生在南部，增加了人们对近期在苏门答腊岛南部近海发生第三次大地震的担忧。这项研究包括对 2004 年和 2005 年苏门答腊岛余震序列和先前区域地震活动进行一系列高精度地震重新定位，并计算苏门答腊岛三维压缩和剪切地震波速度，以便更好地约束热、机械作用在大地震期间，成分、水文和破裂过程沿着俯冲巨型逆冲断层相互作用。 2004 年和 2005 年的主震和余震序列在全球范围内引发了超过 5000 次地震，地震台网沿 1700 公里的俯冲系统记录了这些地震。然而，在苏门答腊地区，俯冲巨型逆冲断层的地震部分主要位于海洋环境内，这最终限制了可用的当地和区域地震数据的数量和覆盖范围，并强调需要最新的数据对可用全球数据的艺术分析。提高精度的地震目录用于细化俯冲带几何形状并探索余震系列内和之间的时空变化。余震与先前区域地震活动之间的比较可以深入了解俯冲带内导致这些大地震的过程，而压缩波和剪切波速度模型与区域地震活动模式之间的比较可以与俯冲巨型逆冲断层破裂行为的变化相关。 该研究分为三个阶段：1) 概率相位重新确定、相位波形互相关以减少拾取误差，以及使用 Engdahl、van der Hilst 和 Buland 方法进行单震地震重定位，2) 高精度相对使用远震双差法计算地震位置，以及 3) 使用远震 DD 断层扫描方法反演三维区域压缩和横波速度模型。 更广泛的影响包括： 1) 所开发的方法显着推进了全球目录和波形数据的使用，以研究高空间密度本地地震仪部署不可行的区域尺度问题，并且所有技术均与公众共享； 2）数据分析和解释涉及本科生、研究生和年轻研究者与地震定位和层析成像领域的知名专家的合作； 3) 该项目涉及万隆技术研究所等五个机构，并加强与印度尼西亚科学界的联系。