Mathematics – Logic
Scientific paper
Jun 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002geoji.149..572s&link_type=abstract
Geophysical Journal International, Volume 149, Issue 3, pp. 572-588.
Mathematics
Logic
5
Empirical Green'S Function Method, Hyogo-Ken Nanbu Earthquake, Slow Rising Initial Phase, Spatio-Temporal Imaging, Transition Process
Scientific paper
Local seismograms of the Hyogo-ken Nanbu earthquake (M 7.2) and its largest aftershocks show that a slow rising initial phase precedes the main P phase. High dynamic range short-period seismograms of the foreshocks, mainshock and aftershocks were recorded by the Japan Meteorological Agency (JMA) network and the NET-HYOGO. Using these seismograms, we investigate the initial rupture process of the mainshock and large aftershocks using an empirical Green's function method. The deconvolved moment rate function of the mainshock shows that it begins with a small pre-event (Mw 4.0), then the moment releases gradually, and after about 0.6 s, it increases rapidly. The first 0.7 s of the deconvolved moment rate functions are inverted to obtain the spatio-temporal images of the initial rupture process. The results show that at the hypocentral area (less than 1 km from the hypocentre) slip velocity rises slowly with a low peak. In the surrounding area, 1 km east and downward from the hypocentre, slip velocity rises rapidly with a high peak. It is also found that during the initial rupture process, the slip velocity pulse grows continuously. These observations are in accord with a theoretical model of the transition process from nucleation to high-speed dynamic rupture in which slip velocity rises slowly at the nucleation zone. We also analyse the initiation and the main dynamic rupture of large aftershocks. Spatio-temporal images of the largest aftershocks (M 5.1 and M 4.8) show that there is a clear initial rupture process with a low moment release and, after about 0.2 s, slip velocity increases rapidly. We compare the initial rupture process of the mainshock with those of the large aftershocks (M 4.0-5.1). The duration (0.6 s) of the initial phase of the mainshock is longer than those (0.02-0.3 s) of the large aftershocks. Furthermore, the slip velocity of the initial rupture process of the mainshock is several times larger than those of the two largest aftershocks. These results suggest that the mainshock starts in the region where the stress drop and fracture energy is higher.
Katao Hiroshi
Nakamura Mamoru
Nakamura Masao
Shibazaki Bunichiro
Yoshida Yasuhiro
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