SCEC Award Number 24187 View PDF
Proposal Category Individual Research Project (Single Investigator / Institution)
Proposal Title Modeling permeability enhancement by earthquakes and fault slip to study fluid-driven earthquake swarms in California
Investigator(s)
Name Organization
Eric Dunham Stanford University
SCEC Milestones B2-2 SCEC Groups FARM, Geology, RC
Report Due Date 03/15/2025 Date Report Submitted 03/17/2025
Project Abstract
 Earthquakes and aseismic slip occur in fault zones that are saturated with fluids. Fault strength depends on pore fluid pressure, which is affected by fluid flow along the fault zone as well as slip and related deformation processes that can cause dilatancy, thermal pressurization, and evolution of fluid transport properties like permeability. Earthquake swarms, like those in California, are thought to be caused by a fluid flow transient and pore pressure increase that triggers seismicity. Fault zone permeability is probably enhanced by aseismic slip and seismicity. While there are laboratory constraints on permeability evolution of sheared gouge layers or slip surfaces, as well as models for hydraulic aperture and permeability changes of natural fractures and joints, there are no models or experimental constraints for permeability enhancement within the fault damage zone through which pore pressure changes are transmitted. In this project, the project team examined the stress concentration around a propagating slip front or rupture and used a Drucker-Prager continuum plasticity model to calculate the evolution of plastic strain in the damage zone. Assuming that permeability increases with plastic strain, the permeability change, integrated over the damage zone in the fault normal direction, is obtained. This provides a quantitative relation between permeability change and slip, from which simple models of permeability enhancement with slip can be calibrated. The project team has incorporated these calibrated models into their earthquake swarm models, which can be used to study naturally occurring swarms in California.
Intellectual Merit This project advanced understanding of fault zone permeability changes with slip by developing mathematical relations to be used in computer simulations of fluid-driven earthquake swarms. Coupled models of fault zone fluid transport and fault slip are increasingly used to study naturally occurring swarms and induced seismicity. These models use a simple, ad hoc permeability evolution model with unconstrained parameters. By modeling inelastic yielding of damage zone rocks, and assuming that permeability increases with inelastic deformation, this project shows that the simple model of permeability enhancement provides an acceptable idealization, justifying its use and providing specific parameter values.
Broader Impacts This project provided training for one PhD student, studying natural hazards using computational modeling, and one postdoctoral fellow, an applied mathematician specializing in numerical methods and scientific computing. This project also helped advance computer simulation capabilities for modeling fluid-driven swarms and aseismic slip, which in addition to occurring naturally, are commonly caused by anthropogenic fluid injection during geoenergy operations. The project team is pursuing applications of this research to induced seismicity occurring in enhanced geothermal systems.
Project Participants The project involved a PhD student and postdoctoral fellow at Stanford University as well as PI Dunham.
Exemplary Figure Figure 1. Permeability enhancement in a fault damage zone from a propagating rupture (Blackstone & Dunham, SCEC poster, 2024). (a) Slip-weakening model for semi-infinite crack propagating at constant rupture velocity, showin drop from peak to residual strength along the fault. (b) Slip and slip velocity. (c) Druker-Prager yield function. Plastic yielding occurs in white region. (d) Plastic strain and (e) normalized permeability increase. (f) Comparison of normalized, width-averaged permeability from the plasticity model (labeled “model B”) with ad hoc model (labeled “model A”), with permeability evolution slip distance L obtained by least squares fitting to minimize the misfit between the two curves.
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