Stress transfer and strain rate variations during the seismic cycle

[1] The balance of forces implies stress transfers during the seismic cycle between the elastobrittle upper crust and the viscoelastic lower crust. This could induce observable time variations of crustal straining in the interseismic period. We simulate these variations using a one-dimensional system of springs, sliders, and dashpot loaded by a constant force. The seismogenic zone and the zone of afterslip below are modeled from rate-and-state friction. The ductile deeper fault zone is modeled from a viscous slider with Newtonian viscosity n. The force per unit length, F, must exceed a critical value Fc to overcome friction resistance of the fault system. This simple system produces periodic earthquakes. The recurrence period, Tcycle, and the duration of the postseismic relaxation phase, which is driven dominantly by afterslip, then both scale linearly with n. Between two earthquakes, interseismic strain buildup across the whole system is nonstationary with the convergence rates Vi, just after each earthquake, being systematically higher than the value Vf at the end of the interseismic period. We show that Vi/Vf is an exponential function of a = Tcycle/TM / Dt/(F Fc) / Dt/(nV0), where Dt is the coseismic stress drop and V0 is the long-term fault slip rate. It follow