Source rupture and ground motion simulations of 1951 Longitudinal Valley Earthquake Sequences and future earthquake scenario

The Longitudinal Valley (LV) in the eastern Taiwan is considered as the suture zone between the Eurasia Plate and the Philippine Sea Plate. Thousands of earthquakes are occur in this area every year. The Longitudinal Valley Fault (LVF) is a seismically active structure, which is located along the LV. During the time period from October to December in 1951, lots of large earthquakes occurred between Hualien and Taitung area, including four major earthquakes (M > 6.9) and thousands of aftershocks. This earthquake series is known as the Longitudinal Valley Earthquake sequence. Coseismic surface rupture with a total length of approximate 90 km were observed along LV. In order to understand the characteristics of source rupture and resultant strong ground motion, this study is comprised of two different parts. In first part, we reconstructed the source model and strong ground motion time history of this earthquake sequence. Inversion of the coseismic displacement data was first conducted. Based on the inverted slip distribution, we performed 3D forward simulation using the Spectral Element Method. Therefore, the second part of the thesis focuses on ground motion prediction for scenario earthquakes. We performed wave propagation simulation with ten stochastic rupture scenarios and examined the results collectively. The numerical simulation results showed that the PGA larger than 250 cm/s2 distributed along LV in eastern Taiwan in all cases. If the rupture started in the middle of LVF, PGA larger than 80 cm/s2 could be detected in the entire island. In the particular stochastic source rupture models, the PGA might be larger than expected in some places far from LVF due to source radiation and directivity effect, such as Taipei basin, Ilan and southern part of Taiwan. The models we presented in this thesis for both historical and scenario events can serve as reference for future in-depth seismotectonic studies and hazard assessment.