2013年吉林前郭M_S5.8震群序列研究

Study on the 2013 Qianguo M_S5.8 earthquake swarm sequence,Jilin,China

对前郭Ms5．8地震后6个月（2013年10月31日～2014年4月30日）内的地震事件进行了重新定位，并利用吉林区域地震台网提供的地震目录研究了序列活动特征。精定位结果显示，余震区呈NW走向分布，长轴约11km，短轴约6km。震源深度为5—15km。结合区域构造特征认为，该序列可能与NW走向的通榆一长春隐伏断裂活动有关，序列具有b值较低、5级地震频次高、发震时间集中的特点。序列主要起伏活动可以分为3个时段：主震后10天，余震强度衰减不明显g此后的2次起伏活动，地震活动分别表现出平静-增强（震级爬升）一发生强震和增强（震级爬升）一平静一再增强（震级爬升）一发生强震的特点；在序列早期阶段，震级一频度无法拟合成1条直线，G—R关系在低震级段和高震级段呈现2个线性段；在Ms5．8地震前h值有变小的趋势，且接近1；而Ms5．8地震后h值明显增大；Ms5．5地震后15天序列衰减比较慢，P值为0．76；Ms5．8地震后15天序列衰减较快，P值为1．17。

The Qianguo Ms5.8 earthquake sequence from October 31,2013 to April 30,2014 were relocated and the seismicity characteristics of the earthquake sequence offered by the Jilin Digital Seismic Network were studied. The results show that the aftershock area is about 1 lkm long in NW strike and 6km width in NE direction. The focal depth is mainly in 5 - 15km. Taking into account the regional structure features, the seismogenic structure involves the blind fault The Tongyu- Changchun fault in NW striking. The sequence is characterized by low b-value,high-frequency of shocks with Ms ≥5.0 and a concentrated temporal distribution. The main activity of the sequence involves three periods. Ten days after the beginning,the attenuation of aftershock density was not obvious. For the two stages later,the seismicity shows characteristics of quiescence-enhancementearthquake and enhancement quiescence-reenhaneement-earthquake. The earthquake frequency with M ≥3.0 and the frequency with M〈3.0 are disproportionate. The gram of G-R relationship shows two linear segments in the high and low magnitude phase respectively. Before the Ms5.8 earthquake,the h-value was getting smaller and closed to 1, while after the Ms5.8 shock, the h-value increased significantly. The p-value, a parameter of modified Omori formula, is small（p = 0.76） 15 days after the Ms5.5 earthquake, and this means that the sequence decays slowly. However after the Ms5.8 earthquake,the sequence decays faster,and p-valve is 1.17.