Xie Zhoumin, Cai Yongen, Wang Chi-Yuen, Yoshioka Shoichi, Tanaka Momo
Institute of Crustal Dynamics, China Earthquake Administration, Beijing, 100085, China.
Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA, 90095-156702, USA.
Sci Rep. 2019 Aug 19;9(1):11987. doi: 10.1038/s41598-019-47992-x.
We predict, with a model (earthquake stress model) that inverts the displacements documented at 163 GNSS onshore stations of the GEONET, the change of shear and normal stresses on the megathrust near the Japan Trench over the seven years before the 2011 Mw 9.0 Tohoku-Oki earthquake. We find three areas on the megathrust with greater accumulations of shear and normal stresses before the earthquake, which match the ruptured areas of the mainshock and two largest aftershocks (M 7.8 and 7.4) that occurred within half an hour after the mainshock. We also find that the change of normal stress on the fault before the earthquake is not uniform but increases in the up-dip portion (shallower depth) of the fault from the hypocenter and decreases in the down-dip portion. We infer that the occurrence of the giant earthquake at the shallow portion of the megathrust may be attributed to the increase of the normal stress there, which leads to an increase of fault shear strength and allows more elastic strain energy to accumulate to prepare for the next big earthquake. Based on these results we propose a new concept of the seismogenic asperity as the area of greater accumulations of shear and normal stresses. The method presented here may be useful for predicting the rupture zone of future large earthquakes.
我们使用一种模型（地震应力模型）对2011年Mw 9.0东北冲地震前七年日本海沟附近巨型逆冲断层上的剪切应力和正应力变化进行了预测，该模型对GEONET的163个陆上GNSS台站记录的位移进行了反演。我们发现在巨型逆冲断层上有三个区域在地震前积累了更大的剪切应力和正应力，这与主震以及主震后半小时内发生的两次最大余震（M 7.8和M 7.4）的破裂区域相匹配。我们还发现，地震前断层上的正应力变化并不均匀，从震源起在断层的上倾部分（较浅深度）增加，在下倾部分减小。我们推断，巨型逆冲断层浅部发生巨大地震可能归因于该区域正应力的增加，这导致断层剪切强度增加，并允许更多的弹性应变能积累，为下一次大地震做准备。基于这些结果，我们提出了一个新的地震孕震asperity概念，即剪切应力和正应力积累更大的区域。这里提出的方法可能有助于预测未来大地震的破裂区域。
