Cs. Wang et al., Westward extension of the Okinawa trough at its western end in the northern Taiwan area: Bathymetric and seismological evidence, TERR ATM OC, 11(2), 2000, pp. 459-480
In this paper, we used detailed bathymetry, earthquake distribution and foc
al mechanisms to study the phenomenon of active westward extension of the O
kinawa trough in the northern Taiwan area, We found a distinguishable subsi
ding and collapsing area on the continental shelf edge and the continental
slope on the northern side of the Okinawa trough, This area extends westwar
ds to at least 121.5 degrees E and includes several morphological units rel
ated to the existence and formation of three major canyons, The canyons and
the morphological units are still evolving through the sediment transport
and through the subsidence and collapse of material due to the formation of
the Okinawa trough. According to the degree of development, we found that
these morphological units have developed from the east to the west, There a
re two parallel E-W trending central graben at the westernmost part of the
Okinawa trough, with each corresponding to a narrow shallow seismic belt, T
he widths of the central graben are 10-15 km, There is geophysical and geol
ogical evidence that the formation of these central graben has been extende
d westwards to the onland area of Taiwan, Focal mechanisms of earthquakes a
nd the topographic features show that the formation of the Okinawa trough i
s associated with the down-dip extensional stress along the subducting slab
of the Philippine Sea plate, and most of northern Taiwan and all the north
eastern offshore area of Taiwan are under tensional stress, New portions of
the Okinawa trough have been forming across the whole width at its western
end through subsidence in the continental shelf, the continental slope and
the traditionally recognized area of the Okinawa trough in the northeaster
n Taiwan area, to make the Okinawa trough develop gradually and extend west
wards.