2013年吉林前郭—乾安震源区中强地震矩张量反演与区域孕震环境研究

Moment inversion of moderate earthquakes and seismogenic environment in Qianguo-Qian'an source region,2013,Jilin Province

2013年10月31日11时03分,在吉林省松原市前郭尔罗斯蒙古族自治县发生M_S5.5级地震,11时10分,震区再发生Ms5.0级地震.截止2013年11月23日,吉林前郭-乾安地区（本文统称为前郭-乾安震源区）已经发生Ms5.0级以上地震5次.虽然震源区外围中强地震活跃,但在前郭-乾安震源区内,据历史地震资料记载,仅2006年3月31日在距离本次地震序列以西8 km处发生过一次乾安、前郭交界Ms5.1级地震.除此之外,距离震源区90 km处,曾于公元1119年2月发生过M6.7级地震.为了更好地认识区域孕震环境,本文利用吉林、辽宁、内蒙古以及黑龙江数字地震台网的三分向宽频带波形资料,建立了适用于这些台站的分区速度结构模型,反演了2013年10月31日-11月23日前郭-乾安震源区M_L≥4.5级中强地震的矩张量解.结果显示,几次中强地震均呈现逆断层兼少量走滑性质,其中NW走向的节面Ⅰ为此次中强地震序列的断层面,发震断层的优势走向集中在320°左右,优势倾角分布在38°-65°.根据矩张量反演结果,结合地震序列重新定位（郑钰,待发表）后的空间分布情况,我们推测此次地震序列的发震构造可能是震源区基底深部一条NW向隐伏逆冲断层,这条断层延伸至地表的位置可能位于震源区北侧靠近124°经度隆起带附近.此外,震源区的发震构造和浅部应力场可能是在西太平洋板块俯冲产生的挤压应力场背景下,受控于郯庐断裂带右行走滑的次级应力场.

Five Ms≥5.0 October 31 and November and Heilongjiang Seismic earthquakes occurred in Qianguo-Qian＇ an, Jilin Province, 23, 2013. Based on the digital waveforms of Jilin, Liaoning, Network, we chose the velocity model respectively for the between Neimeng Songliaobasin and Liaodong anteclise, and analyzed the broadband waveforms with sufficient signal-to- noise levels to invert for seismic moment tensors. Finally we obtained focal mechanism of the moderate earthquakes with the TDMT_ INVC method. The results show that these focal mechanisms of moderate earthquakes in Qianguo-Qian＇an source region are thrust with strike-slip component and the best double couple solution is around 320and 38°-65° for dominant strike and dip. Considering the tectonic settings around the epicentral area and the aftershock distribution, we propose that the focal fault is an unknown base fault in the direction of NW. The seismic structure and shallow stress field in the source region is probably influenced by the secondary stress field derived from the dextral strike-slip of the Tanlu Fault zone under the compression due to the subduction of the western Pacific plate.