Relocation of the 2014 Ms7.3 earthquake sequence in Yutian, Xinjiang

The 2014 M(s)7.3 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(s)7. 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 similar to 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(s)7.3 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.