Insight into the 2017 Mainling M w 6.5 earthquake: a complicated thrust event beneath the Namche Barwa syntaxis

Abstract

Abstract On November 18, 2017, the Mainling M w 6.5 earthquake occurred on the northern Namche Barwa syntaxis and was the largest earthquake in the syntaxis and surrounding areas since the Zayu M w 8.4 earthquake in 1950. Due to inconvenient access and the severe environment in the Namche Barwa syntaxis area, the motions and tectonic structures of most faults remain unclear. Sparsely distributed seismic observation stations make the seismogenic fault and focal mechanism of the Mainling earthquake controversial. We adopt interferometric synthetic aperture radar (InSAR) to invert the slip distribution of this event by defining the fault geometry with relocated aftershocks. Our preferred model suggests that the 2017 Mainling earthquake ruptured two blind faults beneath the Namche Barwa syntaxis. The ruptures were dominated by thrusts with slight right-lateral strike-slip components. The slips on the two faults are equivalent to moment magnitudes of M w 6.12 and M w 6.34, with maximum dislocation magnitudes of 0.36 m and 0.43 m, respectively. The model fits well with the InSAR observations and the distribution of aftershocks. The results from the Coulomb stress simulation indicate that the stress loading caused by strong historical events promoted the occurrence of the 2017 Mainling earthquake. Compared with the seismogenic faults of the Mainling earthquake, the larger thrust faults in the southern Namche Barwa syntaxis can generate larger earthquakes. Therefore, we assume that M w > 6.5 earthquakes may occur beneath the Namche Barwa syntaxis and that the seismic risk has been further promoted by historical events.

Keywords

• 2017 Mainling earthquake
• InSAR
• Slip distribution
• Coulomb stress change
• Seismic risk