| Summary: | 碩士 === 國立中央大學 === 地球物理研究所 === 92 === The purpose of this study is to find out the stress condition in different
homogenous stress zones in the Taiwan region, by method of stress
inversion using focal mechanism data. Numerous focal mechanism data
have been collected from various literatures. The methodology of stress
inversion was the orientation of principal stress axes with the 95%
confidence regions estimated by the Gephart method and Michael method. If
there is a discrepancy between the results of the two methods, the Angelier
method was used for comparison.
Our study area includes the whole island and extends to 30 km offshore.
The range of hypocenter depth is 0 to 30 km. High quality focal mechanism
data obtained from the centroid moment tensor and waveform inversion
algorithm within this zone were collected .
Two dataset were retrieved from the focal mechanism database, group
one is those with magnitude greater than 3 and group two greater than 4 for
more consistent data. The Taiwan region was firstly divided into 9 or 10
homogenous zones by adopting a criteria of misfit less than 6 degrees in the
stress inversion scheme.
The results in each homogenous area show that great majority of
principle stress directions are consistent with the collision between the
Philippine Sea Plate and the Eurasian Plate for the whole study zone. The
eastern side of the Longitudinal Valley can be considered as a homogeneity
of stress field. On the other hand, in Western Taiwan, the direction of most
principal stress changes clockwise from E-W in the South to N in the North.
In I-Lan, near the Okinawa Trough, transtensional faulting mechanism and
more NE-WS maximum horizontal stress direction were found.
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