Source time functions of the 1999, Jiji (Chi-Chi) earthquake from GDSN long period waveform data using aftershocks as empirical Green’s functions |
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| Authors: | Xu Li-sheng G Patau and Chen Yun-tai |
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| Institution: | (1) Institute of Geophysics, China Seismological Bureau, 100081 Beijing, China;(2) Institute de Physiques du Globe de Paris, 75252 Paris, France |
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| Abstract: | A large earthquake (M
W=7.6) occurred in Jiji (Chi-Chi), Taiwan, China on September 20, 1999, and was followed by many moderate-size shocks in the
following days. Two of the largest aftershocks with the magnitudes of M
W=6.1 and M
W=6.2, respectively, were used as empirical Green’s functions (EGFs) to obtain the source time functions (STFs) of the main
shock from long-period waveform data of the Global Digital Seismograph Network (GDSN) including IRIS, GEOSCOPE and CDSN. For
the M
W=6.1 aftershock of September 22, there were 97 pairs of phases clear enough from 78 recordings of 26 stations; for the M
W=6.2 aftershock of September 25, there were 81 pairs of phases clear enough from 72 recordings of 24 stations. For each station,
2 types of STFs were retrieved, which are called P-STF and S-STF due to being from P and S phases, respectively. Totally,
178 STF individuals were obtained for source-process analysis of the main shock. It was noticed that, in general, STFs from
most of the stations had similarities except that those in special azimuths looked different or odd due to the mechanism difference
between the main shock and the aftershocks; and in detail, the shapes of the STFs varied with azimuth. Both of them reflected
the stability and reliability of the retrieved STFs. The comprehensive analysis of those STFs suggested that this event consisted
of two sub-events, the total duration time was about 26 s, and on the average, the second event was about 7 s later than the
first one, and the moment-rate amplitude of the first event was about 15% larger than that of the second one.
Foundation item: State Natural Science Foundation of China (49904004) and IPGP of France.
Contribution No. 02FE2007, Institute of Geophysics, China Seismological Bureau. |
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| Keywords: | Jiji (Chi-chi) earthquake long-period waveform source time function |
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