Modeling Reservoir-Induced Seismicity: A Dynamic Poro-Visco-Elasto-Plastic Earthquake Simulator With Spontaneous Dilatant Coseismic Rupture

Abstract

Compared to other kinds of fluid-related seismicity, reservoir-induced seismicity (RIS) is usually characterized by higher magnitudes. Seismic and water level monitoring and statistical modeling, however, do not provide comprehensive understanding of the RIS mechanism and controls. This study presents a novel finite element method-based 2D poro-visco-elasto-plastic fully dynamic earthquake model, specifically applicable to RIS simulations. A dynamic coseismic rupture phase driven by wave-mediated stress transfers coupled with rate-and-state dependent friction coefficient weakening is modeled, along with interseismic deformations. Coseismic crack opening in a dilatant regime, inducing porosity and permeability hikes, is implemented. The adaptive time stepping resolves the contrasting time scales of coseismic rupturing and quasi-static interseismic deformations, without having to switch the modeling strategy, thereby enabling the modeling of a large number of seismic cycles. The model component verifications demonstrate convincing agreement with theoretical predictions. In the first stage of the simulations, Drucker-Prager plasticity is used to generate a normal fault with enhanced porosity in the Earth's upper crust, over a long time-scale of millions of years. In the second stage of the simulations, RIS is modeled under typical reservoir impoundment dynamics, producing four seismic sequences, triggered by pore pressure increase at the fault at shallow depth below the reservoir. This pressurization is released by aftershocks in every seismic cluster, accompanied by permeability hikes and associated with fault “valving” behavior. The model allows investigation of spatio-temporal RIS characteristics and their controls. It may contribute to earthquake prediction in situ and facilitate earthquake mitigation policies.