The Case Study of Rupture Process and Its Implications beneath the Longitudinal Valley, Taiwan

Abstract:

Taiwan is located at the collision boundary between the Eurasian Plate and the Philippine Sea Plate, and there are frequent seismic activities beneath the eastern part of Taiwan. It is worth to note that most of the earthquakes are shallow earthquakes, therefore, high potential earthquake hazards must be considered. On Oct. 31, 2013, a moderate earthquake (M_L=6.4; depth=15 km) occurred in Ruisui, Hulien area, Taiwan. After seven months, another moderate earthquake (M_L=5.9, depth=18 km) also occurred in the northern part of this area (Fenglin) on May 21, 2014, where the location is nearby the 2013 M6.4 event. Hence, the main goal of this study is to investigate the rupture process of these two earthquakes and tomography structures beneath the Longitude Valley in eastern Taiwan. In this study, we invert a 3-D velocity structure beneath the eastern part of Taiwan. Furthermore, we accurately determine the aftershocks, the related focal mechanisms, and the local stress status from the inverted 3-D velocity model. In addition, we also use both horizontal-components records from the Central Weather Bureau Seismic Network (CWBSN) to invert the source energy radiation pattern by using the isochron method and recursive stochastic technique. The results show that the two earthquakes are energetic and short in duration; with events confined in small source volumes. Base on the above results, we suppose that there might be a NE-SW trending blind fault which dips to the west and the Central Range fault zone leads to a possible oblique slip fault and exhibit high seismic potential. These also imply that this segment of fault zone would be fully cracks before these moderate earthquakes, and then triggered by the local stress field perturbation. This behavior appears to be typical of particularly active plate boundary regions with a highly fractured upper crust under intense tectonic loading.