Abstract
The Tatun volcano group is located adjacent to the Taipei metropolitan area in northern Taiwan and was a result of episodic volcanisms between 2.8 and 0.2 Ma. Earthquake data collected over the last 30 years are analyzed to explore seismicity patterns and their associated mechanisms of faulting in the area. Using a Joint Hypocenter Determination (JHD) method, a few sequences of relocated earthquake hypocenters are tightly clustered; these seemed to be blurry in the original catalog locations. Numerous earthquakes, previously unnoticed and not reported in the CWB catalog, have been identified from careful examination of the continuous recordings of a nearby broadband seismic station. These newly identified earthquakes show similarities in waveforms and arrival time differences between direct P- and S-waves indicating that their hypocenter locations are very close to each other and their source mechanisms are similar. A relatively high b-value of 1.22 is obtained from the analysis of crustal earthquakes (depth < 30 km) in the region, which may suggest that clustered local seismicity in the Tatun volcanic region probably resulted from subsurface hydrothermal or volcano-related activities. Focal mechanism solutions determined in this study are dominated by normal faulting. Thus, these earthquake clusters are most probably associated with hydrothermal/magmatic activities in a back-arc extensional environment.
Highlights
Tatun volcano group in northern Taiwan is located behind the consuming plate margin where the Philippine Sea plate is subducting beneath the Eurasian plate
After the Joint Hypocenter Determination (JHD) relocation, earthquake hypocenters are in general more clustered than the original Telemetered Seismographic Network (TTSN) catalog locations
We have investigated various seismological data collected since 1973 in the Tatun volcano region of northern Taiwan to investigate corresponding seismicity patterns
Summary
Tatun volcano group in northern Taiwan is located behind the consuming plate margin where the Philippine Sea plate is subducting beneath the Eurasian plate. The study region consists of the Tatun Mountain (1,081 m above sea level at its peak) and ~20 other volcanic domes in the surrounding area at the northern end of Taiwan (Fig. 1). Volcanism in this region ceased in the Pliocence (Ho 1988; Song et al 2000) and the region is considered inactive at present. We compare b-values between the Tatun volcano area and the entire island of Taiwan to determine if swarm-type seismicity is persistent. We discuss potential mechanisms of seismicity in the region based on a few focal mechanisms
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