1998年9月15日仙台市で発生した地震(M.5.0)の余震データに基づく応力場の推定

概要

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We estimated stress tensor in the focal area of M5.0 earthquake that occurred on 15 September, 1998, in Sendai city, NE Japan. Many aftershock focal mechanism solutions, which cannot be determined by P wave polarity data alone, were obtained by moment tensor inversion using empirical Green's tensor derivatives. The result of stress tensor inversion based on these mechanism solutions shows that the maximum principal axis of the stress tensor is perpendicular to the strike of Nagamachi-Rifu fault and is consistent with the P axis of the main shock. We found a tendency that events with relatively large mis-fit of slip direction are located around the area with a large slip by the main shock rupture. Stress tensor inversions for 16 subdivided areas show that stress ratio R = (σ1-σ2)/(σ1-σ3) approaches to zero in areas where the slip caused by the main shock rupture is small and aftershock activity is high. These facts suggest local stress field perturbations caused by the slip of the main shock.
東京大学の論文