从同震和震后形变分析日本东北M_W 9.0级大地震对近场地震活动性的影响

The effect of Tohoku M_W 9.0 earthquake on the near-field seismic activity from the coseismic and postseismic deformation

2011年日本东北大地震后,不断有报道认为日本南海海槽可能会发生强震,日本东北大地震对南海海槽断层活动有何影响?本文采用粘弹性半无限空间模型,利用反演得到的日本东北大地震的断层模型,计算了岛内部分断层的同震和震后形变以及库仑应力变化.结果表明:2011年日本东北大地震,使得平行于日本海沟的岛内逆冲断层应力释放明显,5km深度,库仑应力降低值都在50kPa以上,按照该地区每年应力积累1～10kPa计算,相当于释放了5～50年的应力积累;平行于南海海槽的岛内逆冲断层,同震库仑应力增加了1kPa左右,相当于0.1～1年的正常构造运动应力积累;对于岛内的走滑断层,若其滑动方向与同震或震后形变方向一致,则库仑应力增加,反之则降低,如1948年福井地震发震断层库仑应力增加10kPa左右,相当于1～10年的正常构造运动应力积累,地震危险性明显增加.同时,分析了不同软流圈粘滞性对震后形变和库仑应力的影响,发现对于不同的软流圈粘滞性系数,震后的形变和库仑应力相比同震都会有所增加.因此,对于平行南海海槽的岛内逆冲断层和岛内部分滑动方向与同震形变一致的走滑断层,震后地震危险性相比同震会进一步增强.

After the occurrence of 2011 Tohoku Mw 9.0 earthquake, there have been many reports that a strong earthquake maybe occur in Nankai Trough in the future. Does the Tohoku earthquake impact on the seismic activity of Nankai Trough fault？ In this paper, with the viscoelastic half-space model, we calculated the coseismic and postseismic deformation and Coulomb stress change of many faults in the Japanese archipelago. The results showthat： in the 5 km, the 2011 Tohoku Mw 9. 0 earthquake makes the coseismic Coulomb stress of thrust faults paralleling to the Japan Trench release more than 50 kPa, which is equivalent to the stress accumulation of 5 -50 years. While for the thrust faults in the Japanese archipelago paralleling to the Nankai Trough, the coseismic Coulomb stress increase by 1 kPa, which is equivalent to 0. 1 - I years stress accumulation on the case of tectonic movement. For the strike-slip faults, if the sliding direction of the fault is the same with the coseismic displacement, the Coulomb stress will increase, and vice versa. For instance, the Coulomb stress in the fault of 1948 Fukui earthquake increase 10 kPa and the seismic risk is increase significantly. The effect of asthenospheric viscosity on the post-deformation is investigated. We find that the displacement and Coulomb stress will be further increase for most of the faults in the postseismic phase. Therefore, the seismic risk of the thrust fault paralleling to the Nankai Trough and many strike-slip faults whose sliding direction agrees with coseismic displacement, will be enhanced in the future.