南海东部俯冲洋脊区段地震静态库伦应力分析

根据对马尼拉海沟及其邻区地震分布和震源机制解所反映的最大主压应力轴分布特征的分析,并结合古洋脊俯冲区段地震产生的静态库伦应力分析,发现在马尼拉海沟区域地震分布具有明显的分带特性,北部以NW向挤压应力为主,俯冲洋脊区段以近EW向的挤压应力为主;1999年7.2级地震使得2000年6.2级地震和2011年6.0级地震震中位置的静态库伦应力分别增加了约0.5和0.3 bar;2011年6.0级正断型地震和5.0级余震的静态库伦应力变化能较好地反映与余震分布的对应关系,大部分余震位于库伦应力变化值大于0.1 bar的触发阈值区域;计算古洋脊俯冲区段强震产生的静态库伦应力变化,结果显示海沟西侧小于10 km的深度范围内库伦应力增加值达到0.3~0.5 bar,呈NE向展布,吕宋岛弧一侧20 km深度范围内均表现为应力增加,应力增加区域与地震的分布较为吻合。

STATIC COULOMB STRESS ANALYSIS FOR EARTHQUAKES IN THE SPREADING RIDGE OF THE SOUTH CHINA SEA

Based on the distribution pattern of earthquakes and the maximum principal stress direction along the Manila Trench and its adjacent region, combined with the static Coulomb stress analysis for the paleo-ridge segment of the Manila subduction zone, we found the zonal distribution of earthquakes in the northern area of Manila Trench. The maximum principal stresses are dominated by the stress in northwest direction. However, the compressive stress is mainly in eastwest direction in the paleo-ridge segment of the Manila subduction zone. The earthquake with the moment magnitude of 7.2 happened on December 11, 1999 brought about the subsequent 2000 Mw6.2 earthquake and 2011 Mw6.0 earthquake, with an increase of the static Coulomb stresses upto 0.5 bar and 0.3 bar respectively which are closer to the Coulomb failure. The static Coulomb stress change of the earthquake with the moment magnitude 6.0 and the aftershock in a moment magnitude of 5.0 on November 30, 2011,which was caused by normal faults, can better reflect the corresponding relationship of the aftershock distribution. Most of aftershocks are located in the areas with Coulomb stress increased greater than 0.1 bar. The calculation result of the Coulomb stress change of the normal receiver faults imparted from ridge segment shows that the Coulomb stress increased 0.3~0.5 bar in less than 10 km depth ranges and they are mainly along the NE distribution on the ridge segment side. The Coulomb stress increased in an area as deep as 20 km on the Luzon arc side, and is consistent with the earthquakes distribution.