Relocation of the aftershock sequence and activity of the Ms5. 8 Alxa earthquake

On April. 15, 2015, a M(s)5. 8 earthquake with a depth of similar to 10 km shook the Alxa, Inner Mongolia Autonomous Region. In this paper, 138 events from the China Earthquake Networks Center (CENC) standard catalog are used as templates for scanning through seven- month continuous waveform data (Jan. 1, 2015 July. 31, 2015) recorded at 34 stations by using the Match and Locate (M&L) technology. We totally detect 1688 events by using the CENC catalog templates which are ten times more events than listed in the CENC catalog. We then relocate the detected events by applying the double difference tomography (tomoDD) technique. Our relocation results show that the mainshock is located at 39. 8023 degrees N, 106. 4388 degrees E with a focal depth of 20. 597 km. The spatial distribution of aftershocks demonstrates a NEE strike and the depth distribution shows a near-vertical plane. Combining with geological investigation and focal mechanism anlaysis, we suggest that the mainshock is a strike-slip event and the seismogenic fault is likely to be a nearly E-W striking blind fault.