Spatial-temporal distribution of early aftershocks following the 2016 Ms 6.4 Menyuan, Qinghai, China Earthquake

The Lenglongling fault, located in the north Qilian fold zone along the northeastern margin of the Tibetan Plateau, plays an important role in accommodating the tectonic deformation between the Tibetan Plateau and the Alxa block. On 21 January 2016, the Ms 6.4 Menyuan earthquake occurred near the Lenglongling fault. In this study, we utilize the waveform matched filter technique and double-difference earthquake location algorithm to examine the spatial-temporal evolution of aftershocks following the Menyuan mainshock. 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 January 2016 to 31 December 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 (e.g., in the first 10 min or so) 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 occurred in a secondary fault rather than the major Lenglongling fault, which is consistent with geodetic and geological observations. 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.