Stress evolution on the Kunlun fault under the influence of the laterally heterogeneous lower crust

The Kunlun fault is seismically active with successive strong earthquakes. Two seismic gaps along the fault that have not ruptured for several centuries, including the Xidatan and Maqin-Maqu segments, provoke urgent concerns on future seismic hazard. Quantitative analysis of crustal stress evolution, which is controlled by inter-seismic tectonic loading and strong earthquakes, is important for understanding the faulting interactions and estimating future seismic hazard. Here, we construct a 3D viscoelastic finite element model to calculate crustal stress evolution on the Kunlun fault, especially the two seismic gaps. The effects of far-field tectonic loading, inter-seismic fault creep in ductile shear zone, and historical strong earthquakes are analyzed. A series of comparative tests are conducted to analyze the impacts of laterally heterogeneous lower crustal viscosities on faulting stress evolution. Our numerical results show that far-field tectonic loading and inter-seismic fault creep in ductile shear zone lead to Coulomb stress increases at the rates up to 3.0 kPa/yr on the Kunlun fault. The strong earthquakes surrounding the fault induced Coulomb stress increases greater than 20 kPa on the seismic gaps. In addition, lower viscosity in the lower crust of the Baryan Har block and Qiangtang block leads to less stress accumulations on the brittle fault zone in response to far-field tectonic loading and inter-seismic fault creep, but larger post-seismic Coulomb stress changes induced by strong earthquakes. The earthquake recurrence time increases from west to east, corresponding to the spatial variations of the fault slip rates and lower crustal viscosities along the fault. The higher stress accumulations, earthquake recurrences, and elapsed times indicate higher seismic hazard on these two seismic gaps.