2012年2月2日盖州M_L4.7震群序列特征及发震构造探讨

DISCUSSION ON THE CHARACTERISTICS AND SEISMO-TECTONICS OF THE GAIZHOU M_L4. 7EARTHQUAKE SWARM SEQUENCE ON FEBRUARY 2,2012

2012年2月2日盖州ML4.7震群序列随着时间的推移能量释放有逐渐减弱的趋势,期间有2次明显的加速释放过程.双差定位结果显示,盖州震群空间分布主要集中在金州断裂和营口-海城断裂之间,大体呈NW向展布,序列随时间有从金州断裂向营口-海城断裂迁移的趋势,震源深度大部分集中在6 ～ 9km.2月2日发生的2次4级地震的震源机制解P轴方位为94°～120°,这与前人对这一地区区域构造应力场研究的结果基本吻合,表明2月2日发生的盖州ML4.7地震序列是在NWW或近EW向区域应力场作用下,金州断裂走滑错动的结果.但7月12日和11月1日的2次4级地震的P轴方位转变为近NS向,且从精定位结果来看,这2次地震有往NW向营口-海城断裂迁移的趋势,由此推测这2次明显的应力释放过程不单纯是金州断裂滑动的结果,营口-海城断裂也起了一定的作用.声发射等实验结果进一步表明,盖州ML4.7震群的发震构造为NE向的金州断裂和营口-海城2条雁行断裂.该震群的发生可能是金州断裂和营口-海城断裂共同作用的结果,同时也表明在区域应力场作用下,金州断裂和营口-海城断裂有活动的迹象.

During the Gaizhou ML4.7 earthquake swarm sequence on February 2,2012,the energy release weakened gradually with time,accompanied with two obviously accelerated release processes.The double-difference location results show that the spatial distribution of Gaizhou earthquake swarm is mainly concentrated in the area between the Jinzhou Fault and the Yingkou-Haicheng Fault,spreading roughly in NW direction.The sequence showed a trend of migrating from Jinzhou Fault to YingkouHaicheng Fault,and the focal depths are distributed from 6km to 9km.The P-axis directions of focal mechanism of the two ML 4 earthquakes occurring on February 2 are distributed from 94 to 120 degrees,which coincide with the previous studies on the regional tectonic stress field.We could infer that Gaizhou ML 4.7 earthquake sequence on February 2 was caused by the strike-slip faulting of Jinzhou Fault under the action of NWW or near-EW regional stress field.But the P-axis direction of the two ML 4 earthquakes occurring on July 12 and November 1 turned to near NS,and according to the precise relocations,these two earthquakes had the trend of migrating to Yingkou-Haicheng Fault.It is inferred,therefore,that the two obvious stress releases are not only the result of slip of Jinzhou Fault,the Yingkou-Haicheng Fault also played a certain role.Combining with acoustic emission results,it can be further found that seismogenic structure of the ML 4.7 earthquake swarm in Gaizhou is the two en echelon faults,the NE-trending Jinzhou Fault and the Yingkou-Haicheng Fault.This earthquake swarm could be caused by joint action of the two faults.Meanwhile,it also indicates that there are signs of activity of both Jinzhou and Yingkou-Haicheng Faults under the action of the regional stress field.