余震記録に基づく2001年兵庫県北部地震の経験的グリーン・テンソルの推定と本震(<I>M<SUB>J</SUB></I>5.4)の強震動シミュレーション
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概要
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The empirical Green's tensor spatial derivatives (EGTD) method has potential to provide accurate results in simulating strong motion. However, the application of method has been limited so far. The limited use of the EGTD method may arise from the lack of records, because the EGTD method requires a number of waveform data from the same focal zone. Recently, in Japan, the strong motion observation networks, the K-NET and the KiK-net have been operated by the National Research Institute for Earth Science and Disaster Prevention and have accumulated a large amount of strong motion data. Therefore, we consider that we will enhance opportunities to apply the EGTD method to the simulation of strong motion. In this study, we used the EGTD method to simulate the near-filed strong motion records obtained from the mainshock of 2001 Hyogo-ken Hokubu earthquake (<I>M<SUB>J</SUB></I>5.4). One of the K-NET station, HYG004 was chosen as a target station because of its closest epicentral distance (6 to 10km) from the fault zone where the mainshock and aftershocks occurred. Prior to the EGTD estimation, we estimated the strike, dip, and rake of a double-couple point source by applying a grid search technique. In addition, using the fault mechanism estimated by the grid search, we determined the seismic moment and the source time function. The seismic moment released by five sequential slips was estimated by the least-squares method with non-negative constraints. Based on waveform data from 11 aftershocks (<I>M<SUB>J</SUB></I>3.5-4.7) and estimated source parameters, we estimated the EGTD. The data was corrected for the source time function and relative timing to the mainshock. We also rotated the focal mechanisms and correct the station azimuths and take-off angles to compensate the difference in source locations between the mainshock and the aftershocks. The station azimuth of the HYG004 from each epicenter was set to 90° measured clockwise from the north direction, so that the number of unknown elements to be solved was reduced to 3 in radial and vertical components and 2 in transverse component. We performed the inversion independently for each component. Based on the estimated EGTD and source parameters, we simulated the strong motion records for the main-shock. The agreement between the observed and the calculated waveforms is satisfactory for the long duration as well as the amplitude. Through this study, we confirmed that the EGTD method is applicable to the simulation of near-field strong motion based on the data from aftershocks within a extended fault zone.
- 公益社団法人 日本地震学会の論文