Surface Loading and Seismicity in Subduction Zones: Linking Stress Changes to Fault Failure

Non-tectonic processes force the redistribution of mass and surface loading from continental water, ocean water, and the atmosphere at the surface of the earth. These surface loads constantly deform the earth's lithosphere and have been shown to influence seismicity variations in various regions worldwide. This seismicity response provides a probe into the stress state and criticality of active faults. The aim of our study is to assess the influence of these surface loads on the seismicity of subduction zones, where earthquakes with the largest magnitude occur, and to better understand the dynamic interplay between loading sources and seismicity. We compute the subsurface stress changes generated by surface loads from a combination of hydrological, atmospheric, and oceanic models, and compare them to the seismicity of active faults in subduction zones. We use the Global Centroid Moment Tensor earthquake catalogs between 1976 and 2020 and compute the loading-induced stress changes on the fault planes, i.e. normal stress, shear stress, and Coulomb stress changes for each event. We can thus assess if these stress variations constructively add to the local tectonic state of stress, inferred from the focal mechanisms of earthquakes occurring on nearby faults, and promote the faults’ failure. By quantifying the temporal and spatial correlation between surface loads and seismicity, we seek to identify seasonal earthquake modulation conditions and elucidate the underlying mechanisms in global subduction zones.