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.
