PERIODIC LARGE EARTHQUAKES AND SEISMIC
COMPRESSION RATES ACROSS THE COASTAL
RANGE, TAIWAN
Po-Fei Chen
(陳伯飛)
Institute of Earth Sciences, Academia Sinica, P.O. Box 1-55, Nankang, Taipei
The Longitudinal Valley Fault Zone (LVFZ) is the main suture zone in eastern
Taiwan. According to the Harvard CMT catalog (and its extension backwards in time
for Taiwan earthquakes [Chen et al., 2004]), the recent Dec. 2003 Chengkung
earthquake together with the 1972, 1986 events display somewhat periodicity of
large earthquakes (M0 ≥ 1026 dyne-cm) in the vicinity of LVFZ. However, the
variance of the recurrence period of large earthquakes is expected to significantly
increase if we include the 1951 earthquake series, which also calls for the regional
seismic hazard analysis. In this study, first we compile the historical catalog [Lee et
al., 1976] to depict the 1951 earthquake series. Second, together with the Harvard
CMT catalog (the century observations), we investigate the moment-frequency
statistics of the LVFZ earthquakes since 1901. Third, we estimate the seismic
compression rates across the Coastal Range, Taiwan as revealed by earthquakes from
the Harvard CMT catalog.
Combined with earthquake catalog [Lee et al., 1976], field investigation [Hsu,
1961] and earthquake relocation [Yeh et al., 1993], we conclude that the 1951
earthquake series in the LVFZ demonstrates southward propagation of main shocks,
significant components of strike slip motions (left lateral) and unevenly distributed
aftershocks. For both the Harvard catalog only and the century observations, the
moment-frequency statistics roughly predict the frequency of large earthquakes as
derived by observed period dividing by event numbers, despite the fact that the
century observations exhibit significant variance (mean 5.7 years, standard deviation
7.3 years). Upon application of Kostrov[1974]’s formula to relate the averaged strain
rates with the summation of earthquake moment tensors, we estimate the seismic
compression rates across the Coastal Range, Taiwan being 26 mm/yr for northern
LVFZ and 4 mm/yr for southern LVFZ. We will compare the estimated magnitudes
and the along-strike variations with those of GPS observations for future study.