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Moment tensor inversion of regional earthquakes in TaiwanPei-Ru,
JianAbstractBy taking advantage of the establishment of the
Broadband Array in Taiwan for Seismology (BATS), we developed a
procedure of centroid moment tensor (CMT) inversion to overcome
the limitations of conventional first motion solutions and
teleseismic waveform inversions. We then applied this method to
invert source parameters of moderate-sized earthquakes occurred
in the Taiwan region.Our control studies indicated that
epicentral mislocation and erroneous depth of the Moho
discontinuity in velocity model would seriously affect the
inversion results, particularly for single-station inversion.
The work-around is to use low-passed long-period waveforms in
the inversion. The upper limit of allowable frequency band used
in our inversion is determined to be no greater than 0.08 Hz.
There seems to exist a long-period background noise in the
Taiwan region. Such a situation puts a lower limit for the used
frequency band and makes the understanding of detailed velocity
structure more important. Inversion was performed for
earthquakes occurred between Oct. 1994 and Dec. 1996 with ML ≧
4.5. Our results suggested that inversions using multiple
stations is significantly more stable. Stable inversion can also
be obtained by using a few but well-distributed waveforms
propagating mostly through homogeneous tectonic regimes.
Nevertheless, the initial depth used in the inversion sometimes
may converge to a local minimum. Most of the inverted focal
mechanisms can explain P first motions very well with moment
magnitudes comparable to mb、 MS and ML reported by other
sources. We conclude that CMT inversion for regional earthquakes
using BATS waveform data is feasible and stable, provided it
meets certain criteria.
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