Tidal triggering of earthquakes in Longmen Shan region: the relation to the fold belt and basin structures

Abstract

We found a distinctive pattern of tidal triggering of earthquakes related to the fold belt and basin structures. We studied the correlation between tidal variations and seismic events in the Longmen Shan region. We divided this region into two subregions: one is located in the Songpan-Garze Fold Belt which has a soft and weakened crust; the other is located in the Sichuan Basin which has a relatively rigid and strong crust. The results of Schuster's test show that there is a higher correlation in the subregion of the Songpan-Garze Fold Belt than in the subregion of the Sichuan Basin. The reason for this distinctive triggering pattern is that the rock failure mechanism is related to the mechanical properties of the rocks: under conditions of high stress, different kinds of rocks have a different nonlinear behavior of rock deformation and fracture patterns. The nonlinear behavior of rock deformation, which is the prerequisite for a critical stress state in which the tidal stress could trigger an earthquake, increases as the rigidity and the strength of rocks decrease. Therefore, this triggering pattern is closely related to the properties of the crustal rocks of the Songpan-Garze Fold Belt and the Sichuan Basin.