Tomography of the Chukou Fault Zone, Southwest Taiwan: Insights from Microearthquake Data

Abstract

The vigorous collision between the Eurasian plate and Philippine Sea plate in Taiwan causes a series of imbricate fold and thrust belts to develop at the deformation front. The Chukou Fault (CKF), characterized by a thrust type fault, located in Chiayi County, southwest (SW) Taiwan, is a prominent boundary between the fold-thrust belts and the Western Coastal Plain. Most of the seismicity in SW Taiwan is associated with this fault and its neighboring fault systems. The seismotectonic structures in the CKF zone, especially in the east, are complex due to the interactions among fault systems with distinct slip motions. To gain better insights into the seismogenic characteristics in the CKF zone, we used 1661 microearthquakes recorded by a temporary dense broadband seismic network and the Central Weather Bureau Seismic Network (CWBSN) between 2003 and 2004 to investigate the physical properties of the crust in the CKF zone. A waveform cross-correlation technique was applied to 143086 pairs of waveform data to determine the relative differential travel time between the P-and S-waves. By combining both the absolute and relative differential travel time data, we were able to obtain a new 3-D crustal P-wave velocity structure and V p /V s ratios. This study suggests that by using both absolute and relative differential travel time data in tomographic inversion can obtain precise 3-D velocity images and also gain better correlation between seismic events and fault structures, which is crucial for understanding the seismogenic process in our study area.

Diverse Origins of Gases From Mud Volcanoes and Seeps in Tectonically Fragmented Terrane

“…The sites where methane reaches internal equilibrium are primarily distributed in three major structural features: sites CLP, CLS, and KTL in the Chukou fault, site SYNH‐02 in the Chishan fault, and site LS in the Longitudinal Valley fault. The Chukou fault is an east dipping thrust oriented NE‐SW (Yeh et al., 2016). Balanced cross sections suggest that the fault probably represents a complex fault system with subsurface branches forming an imbricate structure and an anticline underneath (Yeh et al., 2016).…”

“…The Chukou fault is an east dipping thrust oriented NE‐SW (Yeh et al., 2016). Balanced cross sections suggest that the fault probably represents a complex fault system with subsurface branches forming an imbricate structure and an anticline underneath (Yeh et al., 2016). The fault and its branches are generally parallel to bedding within the Miocene formation and could be considered as part of the detachment fault extending to a depth of 7–8 km.…”

South Ilan Plain High-Resolution 3-D S-Wave Velocity from Ambient Noise Tomography

“…As a result, the ambient noise tomography method has been widely used to investigate crust and mantle velocity structures (e.g., Lin et al 2007;Huang et al 2012Huang et al , 2015. In comparison with the conventional approach using earthquake sources (e.g., Yeh et al 2016), the merits of this application include that it is free from earthquake source distribution limitations and the resolution depends solely on the station distribution. If dense array data are available, the ambient noise tomography resolutions can be sufficiently high to reveal local geological structures such as sedimentary basins and underground heat resources.…”

Preface to the Special Issue on “Taiwan Earthquake Model: Seismic Hazard Assessment and Earthquake Scenario”

“…On the other hand, the geothermal site, Chingshui is indicated by a low S-wave velocity zone for the upper 1.5 km. Yeh et al (2016) used the data recorded by the Central Weather Bureau Seismic Network and a temporary dense seismic network in the Chiayi area to study the highresolution tomography model of the Chukou fault region.…”