Source inversion and strong ground motion simulation for 1951 Longitudinal Valley earthquake sequence in eastern Taiwan

Abstract:

The Longitudinal Valley (LV) in the eastern Taiwan is considered as the suture zone of Eurasia plate and Philippine Sea plate. Thousands of earthquakes are recorded in this area every year. The Longitudinal Valley Fault (LVF) is an active fault zone which is located from north to the southern end of LV. During the time period from October to December in 1951, lots of large earthquakes occurred between Hualien and Taitung area, which included four major earthquakes (M > 7.1) and thousands of aftershocks were recorded, named the Longitudinal Valley earthquake sequence. Coseismic surface ruptures with a total length of approximate 90 km were observed along LV. In this study, we reconstructed the source model and strong ground motion time history of this earthquake sequence. The LVF is separated into three segments according to segmental characteristics. A source inversion by using the geodetic data was analyzed first. The coseismic displacement of Longitudinal Valley earthquake sequence was taken from the triangulation datasets and interseismic GPS data. The inverted source model showed that the synthetic coseismic displacement had small deviation from the observed data. We took the inversion results to simulate the strong ground motion based on spectral-element method. The simulation results showed that large PGA values distributed mostly in eastern Taiwan along LV and the maximum PGA value was observed in Hualien downtown area which were resulted from the ruptures of northern and central segments. Finally, we reconstructed the numerical earthquake model, including models of source rupture and wave propagation for the 1951 Longitudinal Valley earthquake sequence.