3D-Finite-Element Modelling of Coseismic and Postseismic Coulomb Stress Changes on Intra-Continental Dip-Slip Faults

Investigating the interaction of faults plays a crucial role for assessing seismic hazard. The calculation of Coulomb stress changes allows quantifying stress changes on so-called receiver faults in the surrounding of a source fault that was ruptured during an earthquake. Positive Coulomb stress changes bring receiver faults closer to failure, while a negative value indicates a delay of the next earthquake. Besides the coseismic ('static') stress changes, postseismic ('transient') stress changes induced by postseismic relaxation occur. Here we use 3D finite-element models with arrays of normal or thrust faults to study the coseismic stress changes and the stress changes arising from postseismic relaxation in the lower crust. The results show that synthetic receiver faults in the hanging wall and footwall of the source fault exhibit a symmetric distribution of the coseismic Coulomb stress changes on each fault, with large areas of negative stress changes but also some smaller areas of positive values. In contrast, faults positioned in along-strike prolongation of the source fault and outside of its hanging wall and footwall undergo mostly positive stress changes. Postseismic stress changes caused by viscous flow modify the static stress changes in a way that the net Coulomb stress changes on the receiver faults change significantly through space and time. Our models also allow deciphering the combined effect of stress changes caused by the ongoing extension or shortening (leading to an interseismic stress increase) and by the postseismic relaxation (leading to stress increase or decrease). Depending on the viscosity and the dip and position of the receiver fault, stress changes induced by postseismic relaxation can outweigh the interseismic stress increase such that negative Coulomb stress changes can persist for decades. On other faults, the interseismic stress increase is further increased by postseismic relaxation.