Western Taiwan, and Its Implications for Continental
Margin Deformation
(台灣西部高磁區地殼速度構造及其在大陸邊緣變形之意義)
Win-Bin Cheng (General Education Center, Jin-Wen Institute of Technology)
鄭文彬（景文技術學院通識教育中心）
A joint analysis of gravity anomaly and seismic travel time data have been used to
construct three-dimensional velocity structure for the northeastern extension of the
northern South China Sea high magnetic belt in Taiwan region. Earthquake data were
collected by the Central Weather Bureau Seismological Network from 1991 to 2002.
Gravity data around Taiwan compiled by Hsu et al. (1998) and Wang et al. (2002) was
used in this study. A modified velocity model obtained by local earthquake tomography
(Cheng et al., 2003), was used to constructed an initial three-dimensional gravity model,
using a linear velocity-density relationship. To derive a crustal velocity-density model that
accounts for both types of observations, this study performed a sequential inversion of
traveltime and gravity data. The main features of our three-dimensional velocity model are:
(1) an uplifted zone with velocity greater than 6.5 kms-1 is observed in the lower crust, (2)
the width and the shape of the uplifted zone is found strongly correlated with the high
magnetic belt, (3) the trend of the high-velocity zone turns from NE to N near 23.5°N,
where the feature of high magnetic is offset. A combination of seismic, gravity, and
structural interpretation suggests that the deformation relating to the high magnetic zone in
northern Taiwan could be correlated closely with the collision between the Philippine Sea
plate and the Asian continental margin.