Abstract: We relocated a seismic swarm, which started in a mass from 31 October, 2013 in Qianguo County of Jilin Province, by using double difference location method, based on the phase data of regional digital seismic network and the crustal velocity model of Sunliao Basin. The characteristics of seismogenic fault have been investigated based on the spatial distribution image of the seismic swarm and the geophysical data near the epicenter area. The relocated epicenters of the swarm earthquakes have a precision of 0.9km in E-W, 0.7km in N-S and 1.2km in U-D direction, and show an apparent concentrated seismic belt trending N-W, with a length and width of 12km and 6km, respectively. The source depths of all events are shallow, with 80%in a range of 6~8km, and the events are apparently crowded together on the depth cross section. According to the relocated spatial distribution characteristics of the seismic swarm, the features that the medium size events happened successively, and the focal mechanism of the large size events in the swarm, we infer that the seismogenic tectonics of Qianguo seismic swarm is the thrust nappe structure inside the Keshan-Da'an fault zone. The fault plane inclines to the East direction, and is steep when close to the ground surface, which shows the typical characteristics of a listric thrust fault. The longitudinal length of the rupture plane is greater than the transverse length. According to the features of seismogenic tectonics, we infer that the three M_S ≥ 5.0 earthquakes occurred at the lower layer of the thrust rupture surface of the fault, while the aftershocks were triggered by the three events and occurred mainly at the upper layer of the rupture surface.

Key words: Qianguo seismic swarm, double difference relocation, Songliao Basin, nappe structure

摘要： 基于区域数字地震台网的震相资料、松辽盆地中部地壳速度结构，使用双差定位方法对2013年10月31日开始的吉林省前郭爆发性震群序列进行重新定位。根据重新定位后的地震群空间分布图像结合震中区附近的物探资料探讨发震构造的特征。重定位后EW、NS和UD 3个方向大致的定位精度分别为0.9km、0.7km和1.2km，地震序列震呈NW向密集条带状分布，长度约12km，正交NE向，宽约6km。震群序列中地震震源深度较浅，80%的地震分布在6~8km深度范围内，在深度剖面上震群序列表现为明显的密集现象。根据重新定位后震群序列的空间分布特征、序列中等震连发特征以及较大级别地震的震源机制解，推断发震构造为克山-大安断裂带内的推覆逆冲构造。冲断面向E倾斜，近地表倾角较陡，深部几乎平直，表现为典型的铲形逆冲断层的特征，断层面纵向破裂长度大于横向破裂长度。根据发震构造的特征可以推断3个5级地震发生在下层冲断面上，余震主要在冲断面上部触发。

关键词: 前郭震群, 双差定位方法, 松辽盆地, 推覆构造