Insight into the 2016 Menyuan Mw 5.9 Earthquake with InSAR: A Blind Reverse Event Promoted by Historical Earthquakes

Abstract

In 2016, the Mw 5.9 Menyuan earthquake occurred at the western end of the Tianzhu seismic gap in the middle segment of the left-lateral strike-slip Haiyuan fault system. Studying the focal mechanism of the Menyuan earthquake and its correlation with historical seismicity is of great significance in understanding the tectonic style of the Haiyuan fault system and assessing the Tianzhu gap seismic risk. Using Sentinel-1A radar imagery, we obtain the coseismic deformation field of the Menyuan earthquake in the LOS direction and invert the deformation field slip distribution model. Based on the interseismic deformation field reflected by GPS data and the relocated results of aftershocks provided by previous studies, we then analyze the seismogenic nodal plane of the Menyuan earthquake and consider the west-dipping model to be the most likely seismogenic solution. The west-dipping model indicates that the average slip of the Menyuan earthquake is 0.41 m, and the average rake angle is 68°, with a magnitude of Mw 5.905. Considering the historical strong earthquakes and viscoelastic layered crust, the results from Coulomb failure stress modeling indicate that the Coulomb stress loading caused by the historical strong events promoted the occurrence of the 2016 Menyuan earthquake. Both the low seismicity within the Tianzhu gap and the cluster phenomenon of medium earthquakes on the Lao Hu Shan (LHS) and Leng Long Ling (LLL) faults have strong correlations with the stress change distribution resulting from the historical strong earthquakes. A series of medium events occurring on the north side of the LLL fault, represented by the 2016 Menyuan earthquake, would raise the seismic risk on the western end of the Tianzhu gap.