台灣東部地區淺源地震再定位及其構造含意之探討
Other Title
Relocation of the crustal earthquakes in the eastern Taiwan
and its tectonics implication
and its tectonics implication
Date Issued
2004
Date
2004
Author(s)
DOI
922119M002026
Abstract
We relocated 6173 shallow
earthquakes and determined focal
mechanism solutions of thirty-three ML ≥
5.0 events in the eastern Taiwan region
(bounded by 22.7 N, 120.8 E ; °°
24.5 N, 121.5 E; 24.3 N, 122.3 E °°°°
and 22.5 N, 121.6 E) in order to °°
investigate their tectonic implications.
Our results suggest that the distribution
of the relocated earthquakes generally
agrees with the fault plane determined
from the focal mechanism solutions. The
Longitudinal Valley (LV) is an
east-dipping seismic suture zone that
separates two different tectonic regions.
On the left-hand side of the LV, shallow
earthquakes and normal fault-type focal
mechanism were found in the Central
Range region. But on the right-hand side of the LV, most events occurred in the
Philippine Sea Plate (PSP) were of the
thrust-type, especially for the south
portion and a few normal and strike-slip
focal mechanism events were observed in
the north portion. The tectonics of the
eastern Taiwan can be classified from
south and north into two regions, and
there may exist a structure or boundary at
about latitude 23.5°N with a strike of
N110°E. In the northern portion of the
eastern Taiwan, the plate boundary
appears to be an east-dipping plane
defined by the earthquake distribution.
The focal mechanism solutions
determined in this zone show thrust type
faulting and agreed with this boundary
plane (strike N20°E and dip about 50°).
In this region, the Eurasia Plate (EP) dips
to the east, and the PSP bends and dips to
west. Thus, the shallow earthquakes with
normal and strike-slip focal mechanism
were observed in the offshore area of this
region. On the other hand, the southern
part of the eastern Taiwan is a simple
tectonics condition. The EP subducts to
the east under the PSP. The LV is a suture
zone dipping to the east, and most events
occurred on the right-hand side of the LV.
Focal mechanism solutions of these
events were thrust-type with strike about
N25°E and dip 54° to the east.
Subjects
Earthquake
Focal mechanism
solution
solution
Tectonics
EasternTaiwan
Plate
boundary
boundary
Publisher
臺北市：國立臺灣大學地質科學系暨研究所
Type
report
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