Abstract
In this study, we adopt a damping least-square inversion method to investigate the Vp structures and Vp/Vs ratios of the crust and upper mantle beneath the Chia-Nan area, Taiwan. Previous studies have shown that, velocity structure can be used as an indicator of the geometry of a fault and the general aspects of tectonics. Therefore, the first goal of this research is to analyze the degree of correlation between the velocity structure and the seismic characteristics with respect to the tectonic implications of the area. The second intention is to study the relationship between the Vp/Vs ratio and the pressure change occurring with crack opening in the deeper crust. Finally, the distribution of Vp/Vs ratios and its association with fault activities is also investigated. Our results indicate that the variations in velocity structure beneath the Chia-Nan area is caused by local geological structures, fault crossing and the existence of the Pei-Kang High Area. We also find that most earthquakes occur in areas that have Vp/Vs gradients varying rapidly. In addition, according to the distribution of the earthquakes, there seems to exist a westdipping fault west of the Chukou fault; however, this prospect needs to be investigated further in a future study.
Highlights
Taiwan is located at the convergent boundary of the Eurasian Plate and the Philippine SeaPlate
The first section discusses the results in terms of how velocity structures and Vp/Vs ratios were derived
This discussion will be accompanied by an examination of the resolution, standard error and the relative distribution of derivative weight sum (DWS)
Summary
Taiwan is located at the convergent boundary of the Eurasian Plate and the Philippine SeaPlate. Taiwan is recognized as a complex and tectonically active region (Suppe 1984; Ho 1986; Liu et al 1997; Wu et al 1997). According to several studies of earthquakes in Taiwan (Cheng et al 1998), there have been about one hundred destructive quakes during the 20th century. Most of the earthquakes occur in the eastern and northeastern seismic zones, the Chia-Nan Plain in southwestern Taiwan has been known as an area that produces many destructive earthquakes (e.g., Chia-Li 1991; Tapu 1993; Rei-Li 1998; Chia-Yi 1999). In order to have a better understanding of the characteristics of earthquakes occurring in the Chia-Nan area, it is very important to understand the velocity structures beneath the Chia-Nan Plain
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