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Simulation of Sequence of Induced Earthquakes and Aseismic Slip Due to Injection Into a Hydrologically Isolated Rate and State Fault

Session: Mechanisms of Induced Seismicity: Pressure Diffusion, Elastic Stressing and Aseismic Slip I

Type: Oral

Date: 4/19/2021

Presentation Time: 02:15 PM Pacific

Description: 

Reducing hazard of induced seismicity continues to be a major challenge in several geo-energy applications and related activities including CO2 sequestration and waste-water injection. A key to address this challenge is developing tools for modeling the full fault history of earthquakes and aseismic slip in response to pore pressure and poroelastic stress perturbations to understand the interplay between different time and spatial scales involved with friction, fluid diffusion, and stress transfer. Here, we simulate sequence of earthquake cycles with evolving pore pressure for an anti-plane fault using a hybrid finite element-boundary integral method with alternating quasidynamic and fully dynamic schemes. We consider a vertical rate-and-state fault embedded at depth within a linear elastic half-space. Fluid is assumed to be injected directly to the fault core and pore pressure diffusion is determined analytically constraining it to the fault parallel direction with modification for free surface boundary condition.

We show that the seismicity pattern depends on the injection location and whether it is in the velocity strengthening (VS) or the velocity weakening (VW) regions in the fault. Pre-injection periodic pattern of seismicity is broken by injection leading to space time clustering of the events, accelerated slip accumulation, and reduced inter event time. There is also a delay in recovery to the original pre-injection state after stopping injection. During injection, clustering of intermediate events with partial rupture are found for injection near the transition between VS and VW regions. For injection within the VW region, we observe a period of seismic quiescence after injection shut off, followed by the largest seismic event in the sequence. Our results highlight the interplay between fault rheological heterogeneities and pore pressure diffusion and suggests that delayed seismicity after injection shut off may occur even in the absence of poroelastic effects. These observations are critical for planning mitigation scenarios of induced seismicity risk.

Presenting Author: Md Shumon Mia

Student Presenter: Yes

Authors