Spatio-temporal seismicity changes and high-resolution fault zone structures associated with recent large earthquakes in China

大地震发生在主要的断层带上。获得大地震前后地震活动的时空变化和详细的断裂带性质是地震地震学长期追求的目标。有时，在大的浅层地震之前，地震活动增加，也被称为“前震”。然而，前震、主震成核与断裂带构造之间的确切关系仍存在争议。近年来，中国青藏高原周边发生了几次大地震，造成了重大的经济损失和人员伤亡。这些地震包括2008年7.3级的玉田地震、8.0级的汶川地震、2010年7.0级的玉树地震、2013年7.0级的庐山地震和2014年7.3级的玉田地震。其中，玉树和玉田主震有明显的M4-5前震证据，汶川和芦山主震没有。，全面的分析可以让我们更好地了解前震是否存在及其物理机制。该项目将支持一个团队对中国这些大地震前后的地震活动性变化进行系统检查，并对断裂带结构进行高分辨率成像。这项研究将采用每次主震附近的永久地震台站记录的连续波形，以及密集的余震部署。为了研究地震活动性和断裂带过程的演化变化，研究人员计划进行以下任务：(1)使用最近开发的波形匹配滤波技术在每次主震发生之前很久就检测到所有地震；(2)利用新定位目录搜索主震前时空演变，进行流行病型余震序列（ETAS）建模，推导震源属性；(3)沿近期几次地震的破裂带确定断裂带头波；(4)联合反演P和fzhw，获得高分辨率断层界面属性。通过多面技术和广泛的波形数据，他们希望获得地震活动演变的更完整的图像，以及它们与中国几次大型板块内地震震中周围断裂带过程的关系。这个项目可以提供重要的新证据，证明在大主震之前存在（或缺乏）前兆变化。所获得的结果对于评估在这些地区使用前震作为预测工具和减轻地震灾害至关重要。该项目将开发新探测到的地震目录等数据产品，并通过同行评审的出版物与其他研究人员共享。该项目将支持研究生和本科生实习生在中国进行科学研究，促进国际合作。该项目由ISE全球创业基金共同支持。

Large earthquakes occur on major fault zones. Obtaining spatio-temporal changes of seismic activities and detailed fault zone properties around the times of large earthquakes are long-sought goals in earthquake seismology. Sometimes large shallow earthquakes are preceded by increased seismic activity also known as ?foreshocks?. However, the exact relationship among foreshocks, mainshock nucleation and fault zone structures are still in debate. Recently several large earthquakes occurred around the Tibetan Plateau in China, and produced significant damages and casualties. These include the 2008 Ms7.3 Yutian, Ms8.0 Wenchuan, the 2010 Ms7.0 Yushu, the 2013 Ms7.0 Lushan, and the 2014 Ms7.3 Yutian earthquakes. Among them, the Yushu and Yutian mainshocks had clear evidence of M4-5 foreshocks, while the Wenchuan and Lushan mainshocks did not., a comprehensive analysis could provide us a better understanding on whether foreshocks exist and their physical mechanisms. This project will support a team to conduct a systematic examination of seismicity changes around the times of these large earthquakes in China, as well as high-resolution imaging of fault zone structures. The study will employ continuous waveforms recorded by permanent seismic stations around the region of each mainshock, as well as dense aftershock deployment. To examine evolutionary changes in seismicity and fault zone processes, the researchers plan to conduct the following tasks: (1) Use a recently developed waveform matched filter technique to detect all earthquakes long before the occurrence of each mainshock; (2) Use newly relocate catalogs to search for spatio-temporal evolutions before mainshock, as well as performing Epidemic Type Aftershock Sequence (ETAS) modeling and deriving source properties; (3) Identify fault zone head waves along the rupture zones of several recent events; and (4) Perform joint inversion of P and FZHWs for high-resolution fault interface properties. With multi-facet techniques and extensive waveform data, they look to obtain a more complete picture on evolutions of seismic activities and their relationship with fault zone processes around the epicenters of several large intra-plate earthquakes in China. This project can provide important new evidence on the existence (or lack of) precursory changes that precede large mainshocks. The obtained results are essential for evaluating the use of foreshocks as forecasting tools and seismic hazard mitigation in these regions. The project will develop data products such as newly detected earthquake catalog and share with other researchers via peer-reviewed publications. This project will support both graduate students and undergraduate interns to conduct scientific research in China, and promote international collaboration. The project is co-supported by the ISE Global Venture Fund.