Seismotectonic Structure Associated Collision Zone
Between the Philippine Sea Plate and the Eurasian
Plate along the Longitudinal Valley and Coastal
Range of Eastern Taiwan
Kwang Hee Kim1, Kuo-Fong Ma1, Horng-Yuan Yen1, Chien-Hsin Chang2,
Kuo-Cheng Chen3, and Jer-Ming Chiu4
(金廣熙、馬國鳳、顏宏元、張建興、陳國誠、邱哲明)
1
: Institute of Geophysics, National Central University
2
3
1
: Central Weather Bureau
: Institute of Earth Science, Academia Sinica
: Center for Earthquake Research and Information, the University of Memphis
Using earthquake data collected by an island-wide seismic network and two
temporary seismic arrays/networks, high-resolution 3-D velocity structural images
beneath an oceanic-continental collision zone along the Longitudinal Valley (LV) and
Coastal Range (CR) in eastern Taiwan are imaged. A revised nonlinear travel time
tomography method of Benz et al. (1996) was applied to determine a reliable 3-D Vp
and Vs velocity structure. A newly developed single-event location algorithm using
the resultant 3-D Vp and Vs velocity model (Chiu et al., 2003; Chen et al., 2004) has
been applied to obtain reliable hypocenters. The relationship between seismicity
and the 3-D velocity structural model as well as their tectonic implications can thus
be vivid explored. In general, seismicity along the collision zone is not uniformly
distributed and follows mainly the north-south trending regional tectonic orientation.
A well-defined eastward dipping seismic zone extending to a depth ~20 km can be
clearly identified in the southern collision zone and can be associated with a region
of high Vp and high Vp/Vs ratio revealing that earthquakes in this region occurred
mainly along a highly fractured or fluid rich zone relating to the early phase of plate
collision. On the contrary, a well-defined westward dipping seismic zone extending
to a depth ~25 km can be clearly identified in the northern collision zone and can be
associated with a region of advanced collision along a transition zone separating the
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high velocity oceanic crust to the east and the lower velocity continental crust to the
west. The transition in central collision zone between the eastward and westward
dipping seismic zones is characterized by a relatively low seismicity corresponding
to a region of high heat flow and high geothermal activities. Below the
low-velocity material in the upper crust of the collision zone, the P-wave velocity
increases rapidly to 7.0 km/sec at about 12~14 km depth indicating either a thin crust
or high velocity materials of deep origin.
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