2021年玛多M_(W)7.4地震超剪切破裂的动力学机制

Dynamic Mechanisms of Supershear Rupture of 2021 Maduo M_(W)7.4 Earthquake

采用有限元方法模拟2021年青海玛多M_(W)7.4地震断层产生自发破裂的传播过程,以断层的观测滑移量为约束条件,通过网格搜索方法寻找最优模型。结果表明:1)震源东侧的断层弯折结构是产生突然超剪切破裂的关键因素,这一特殊几何结构使破裂在成核后3~4 s内就产生了超剪切破裂,这与传统超剪切破裂需要很长破裂传播距离的现象不一致;2)玛多地震震源东侧断层产生超剪切破裂,而西侧断层破裂表现为亚剪切,这与通过地震学及大地测量学反演震源破裂过程得到的结果一致;3)断层阶区、平直断层等其他断层的几何结构并不能使玛多地震产生突然的超剪切破裂现象。

We use finite element method to simulate the spontaneous rupture propagation process on the fault of the 2021 Maduo M_(W)7.4 earthquake.Through a grid search method,we identify the optimal model for the seismic fault.Numerical simulation results indicate that:1)The key factor inducing the sudden supershear rupture transformation is the fault bend fold structure on the east side of the epicenter.This unique geometric structure triggers the supershear rupture transformation approximately 3 to 4 seconds after nucleation.This is inconsistent with the phenomenon that the traditional supershear rupture requires a long propagation distance.2)The faults on the eastward side of the epicenter display supershear rupture in Maduo earthquake,while the westward rupture exhibits subshear behavior.This result is consistent with the findings obtained through seismological and geodetic inversion of the earthquake source rupture process.3)Other fault geometric structures,such as fault stepover or straight faults,do not contribute to the sudden supershear rupture in Maduo earthquake.