2014年新疆于田MS7.3级地震序列重定位

2014年新疆于田发生MS7.3地震,这一地区6年来连续发生2次强烈地震,震中相距不到110km.由于初始定位误差较大,于田地震的发震断层仍不清楚.本研究的主要目标是利用地震精定位方法对于田地震序列及其背景地震活动进行重新定位,确定于田地震的发震断层.本研究使用双差定位方法对于田地震序列进行重新定位.这一方法假设两个地震的震源距小于事件到台站的距离,两个事件到同一台站的走时差主要归因于其空间位置的偏移,因此可消除由于速度模型不准确引起的定位误差.重定位后得到了435个地震的位置参数.结果表明,2014年于田MS7.3级地震发生在阿尔金断裂带的西端,余震分布的优势方向为北东向,展布长度约33km,震源深度主要集中在4~12km,多数余震位于主震的西南侧.NS,EW和UD方向的定位误差分别为0.5km,1.1km和1.7km.于田地震余震序列总体衰减较慢.根据余震分布特征和震源机制解,认为此次地震的断层面为北东向的节面,阿尔金断裂的西南延伸分支断层是这次地震的主要发震构造.于田地震的发生与巴颜喀拉块体的东南向运动有关.

Relocation of the 2014 MS7.3 earthquake sequence in Yutian,Xinjiang

The 2014 M_S7.3 Yutian earthquake occurred at the west end of the Altun fault. Two strong earthquakes struck this region within 6 years. Due to the large uncertainty of initial earthquake location, the causative fault of the Yutian earthquake is still unknown. The objective of this research is to determine the causative fault with fine-scale earthquake relocation method.The Yutian earthquake sequence was relocated using the Double Difference algorithm (HypoDD). This method minimizes errors introduced to earthquake locations by unmodeled two- or three-dimensional velocity structure by assuming that the spatial separation between hypocenters is small compared to the hypocenter-station distance, and therefore velocity variation is the same along event-pair raypaths.We relocated 435 earthquakes in the Yutian region. The earthquake relocation results show that the Yutian M_S7.3 earthquake occurred at the west end of the Altun fault. The epicenters of its aftershocks are distributed mainly along both sides of this fault with north-east direction. Most of the aftershocks are located to the southwest of the mainshock. The aftershocks spread approximately 33 km in length. The focal depths are confined in a depth range of 4~12 km. The location error in NS, EW and UD direction is 0.5 km, 1.1 km and 1.7 km, respectively. The aftershock sequence of the Yutian earthquake decayed slowly.According to the characteristics of the aftershock distribution and focal mechanism solutions, we speculate that the fault plane of the M_S7.3 earthquake is oriented north-east. The causative fault of the Yutian earthquake is a branch of southwestern part of the Altun fault.The occurrence of the Yutian earthquake might result from the southeastward movement of the BayanHar block.