Spatial-temporal Evolution of Microseismicity and Repeating Earthquakes Following the 2016 Ms 6.4 Qinghai Menyuan Earthquake

On 21 January 2016, the Ms 6.4 Menyuan earthquake took place near the Lenglongling fault. In this study, we apply a waveform matching technique to obtain a detailed aftershock catalog with emphasis on its early aftershock sequence. Events from both China Earthquake Networks Center (CENC) routine catalog and relocated catalog are used as templates to scan through the continuous waveform data (21 Jan. 2016 to 31 Dec. 2016). We identify three and eleven times more events than listed in CENC routine catalog and relocated catalog, respectively. We find that the earliest aftershocks mostly illuminated a steeply dipping plane, while aftershocks at later times outlined a near vertical dipping plane with mostly strike-slip focal mechanisms. The relocated aftershocks also suggest that the Menyuan mainshock took place in a secondary fault rather than the major Lenglongling fault. Moreover, we find that aftershocks systematically expand with time along the fault strike and 16 repeating earthquake clusters occur in the rupture zone, which are likely driven by afterslip of the mainshock.