Unraveling scaling properties of slow slip events and their interplay with large megathrust earthquakes

Abstract:

Large megathrust faults produce a wide spectrum of slip modes, ranging from earthquakes to slow-slip events (SSEs). SSEs appear to have slip mechanisms similar to those of regular (fast) earthquakes and are often located in neighboring regions of the seismogenic zone. However, whether SSEs and regular earthquakes arise from similar failure mechanisms, and how different slip behaviors are separated in space and time, are still a matter of debate. We examine the scaling properties of SSEs using 3D dynamic simulations of frictional sliding in fault model of a velocity-weakening fault strip surrounded by velocity-strengthening areas on a rate-and-state fault with inelastic dilatancy and fluid overpressure. Simulated SSEs follow the Gutenberg-Richter law and obey a cubic moment-duration scaling law — similar to that of fast (regular) earthquakes — as observed in Cascadia. In contrast to conventional and widely used assumptions of magnitude-invariant rupture velocities and stress drops, both simulated and natural SSEs have rupture velocities and stress drops that increase with event magnitudes. The success of our model in reproducing a realistic sequence of SSEs that provides an excellent match to a number of observations collected along the Cascadia megathrust indicates that rate-and-state friction combined with pore fluids effects is a plausible physical mechanism for SSEs. We will also report on our current modeling work examining the interplay of the SSEs with large megathrust earthquakes occurring in a shallower seismogenic fault region. Our goal is to shed lights on how large megathrust earthquakes affect the spatiotemporal properties of SSEs during the centuries-long interseismic periods and, in turn, how the occurrence of frequent SSEs affect the location and timing of large megathrust earthquakes. These studies will help advance our understanding of the frictional behavior relevant to SSEs, earthquake nucleation, and triggering and determine whether interactions between the seismogenic zone and SSEs can be used to constrain the occurrence of large, destructive earthquakes.