| Summary: | 碩士 === 國立中央大學 === 地球物理學系 === 84 === We investigated the source characteristics of the May 24, 1994
Hualien(ML=6.6)、June 5,1994 Nanao(ML=6.2) and June 25,1995
Ilan (ML=6.5)earthquakes using the long-period P-wave data
recorded by the IRIS (Incorporated Research Institution for
Seismology) and local strong motion data obtained from CWB
(Central Weather Bureau). For teleseismic study，we applied
complex body waveform inversion method to determine the source
time function and focal mechanism. The results show that the
1994 May event was a thrust fault mechanism and resulted from a
complex rupture process with source duration extending to 35
seconds. The earthquake took place on June 25,1995 shows a
normal fault mechanism with source duration just as 3 seconds.
According to the spectra analysis using teleseismic data, we
obtained moment magnitude，Mw，of the three earthquakes of
6.7、 6.3 and 5.7，respectively. The stress drop calculated
from the corner frequency measured from the spectra were also
obtained. The stress drop differences of the June 25, 1995
event from the others implies that the tectonic structure of
June 25, 1995 differs from the June 5, 1994 and May 24, 1994
earthquakes. The local strong motion data of June 25, 1995
earthquake shows the variation of pulse width of SH wave with
azimuth. From the discussion of directivity，we believed this
azimuthal variation was caused by rupture directivity。The
actual fault plane of the earthquake is strike=133.5°、dip=61.2
°and rake=34.6°。The rupture direction of the fault plane is
from southeastern to northwestern。The result is consistent
with that from Joint Hypocenter Determination(JHD)。
|
|---|
