Coupled Models of Fault Slip and Fault-Zone Fluid Flow Produce Earthquake Swarms and Aseismic Slip

Abstract:

Earthquake models typically prescribe the normal stress and pore pressure on faults, with slip dynamics determined solely by the interaction of friction and elasticity. But many observations attest to the importance of pore pressure dynamics and fault-zone fluid flow in producing earthquake swarms, injection-induced seismicity, and aseismic slip. Here we explore the coupled dynamics of frictional slip and pore pressure in models that account for permeability and porosity evolution from mechanical processes like pore dilation and chemical processes like healing and sealing. Our models reproduce fault-valving behavior, in which a steady fluid source at depth intermittently releases pulses of high pore pressure than ascend along faults, triggering aseismic slip and producing swarm seismicity. Under certain conditions, periodic slow slip events emerge spontaneously at the base of the seismogenic zone, with features bearing similarity to long-term slow slip events in subduction zones. We also explore injection-induced seismicity, focusing on aseismic slip driven by injection into a fault zone. Constant rate injection into a velocity-strengthening fault drives aseismic slip outward at a constant rate. Our model reproduces observed migration rates of microseismicity, at least when we assume that microseismicity tracks the aseismic slip front. We explore how injection rate and other model parameters influence the slip front migration rate, and close by linking our model to observations of injection-induced aseismic slip on normal faults in the Delaware Basin.