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.

俯冲带大地震造成的地震和海啸危险早已得到承认，但鉴于2004年12月26日苏门答腊-安达曼群岛发生的Mw 9+地震，由此引发的海啸，基础设施破坏和巨大的生命损失，显然，这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的四大地震之一，在许多方面可与1960年智利Mw9.5和1964年阿拉斯加Mw9.2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重大破坏和海啸。苏门答腊-安达曼群岛事件引发了第二次大地震，2005年3月28日的Mw8.7尼亚斯事件，直接向南，增加了对苏门答腊南部近海在短期内发生第三次大地震的担忧。这项研究包括一系列高精度的地震重新定位的2004年和2005年苏门答腊余震序列和先前的区域地震活动性和计算的压缩和剪切地震波速度在三维的苏门答腊地区，以更好地约束如何热，机械，成分，水文和破裂过程中相互作用沿着俯冲巨型逆冲断层在大地震。2004年和2005年的主震和余震序列产生了超过5000个地震记录的全球地震台网沿沿着1700公里的俯冲系统。然而，在苏门答腊地区，俯冲巨型逆冲断层的孕震部分主要位于海洋环境中，这最终限制了将可获得的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。精度提高的地震目录被用来完善俯冲带的几何形状，并探讨余震系列内和之间的时空变异。余震和以前的区域地震活动之间的比较提供了深入了解的过程中，导致这些大地震的俯冲带，而压缩和剪切波速度模型和区域地震活动模式之间的比较，可以与断裂行为的变化沿着俯冲巨型逆冲断层。 该研究分三个阶段进行：1）概率震相重定，震相波形互相关以减少拾取误差，以及使用Engdahl，货车der Hundle和Buland方法的单次地震重定位，2）使用双差方法的高精度相对地震定位，（3）利用双折射DD层析成像方法反演区域三维纵横波速度模型。 更广泛的影响包括：1）所开发的方法显著推进了全球目录和波形数据的使用，以研究高空间密度的地方地震仪部署不可行的区域尺度问题，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、研究生和年轻的研究人员与地震定位和断层摄影领域的知名专家合作;该项目涉及五个机构，包括万隆技术研究所，并加强与印度尼西亚科学界的联系。