Impact of climatically induced surface mass changes on the earthquake cycle of intra-plate thrust faults: Insights from numerical modelling

Modern global warming causes enhanced melting of ice bodies and desiccation of lakes worldwide. The surface mass changes that occurred over the past decades were sufficiently large to cause discernible crustal deformation and alterations of seismicity patterns in the respective regions. As these climatically induced mass changes will continue to affect continental interiors in the future, assessing their impact on crustal deformation is crucial for future seismic hazard estimates. Here, we use numerical modelling to explore how such climate-induced unloading of Earth's crust may affect the earthquake cycle of thrust faults in continental interiors. In different 2D experiments, we vary the magnitude and width of the load, the duration of unloading, the length of the interseismic phase, the viscosity of the lower crust and the shortening rate to capture low-strain and tectonically active settings. All experiments show that the fault responds to unloading with increased coseismic slip. When unloading phases are equal to or shorter than the interseismic phase, the largest amount of slip occurs toward the end of the unloading period. Even if the load is removed during a single interseismic phase, enhanced coseismic slip may also occur up to thousands of years after unloading. Generally, the increase in coseismic slip is most pronounced for large and narrow loads, long recurrence intervals, low shortening rates and low viscosities of the lower crust. Our findings imply that climate-induced unloading has the potential to increase earthquake magnitudes, to shorten earthquake recurrence intervals, and to increase the earthquake hazard especially in low-strain regions.
Compared to earlier studies, our results provide first insights into the impact that is to be expected from the ongoing deglaciation of glaciers and ice sheets worldwide on the coseismic slip of faults and hence, on approximate earthquake magnitudes. With respect to modern climate change, our results indicate that climate-induced mass changes on Earth's surface have the potential to increase the seismic hazard in various geological settings.