Fault valving and pore pressure evolution in simulations of earthquake sequences and aseismic slip

Abstract

Fault-zone fluids control effective normal stress and fault strength. While most earthquake models assume a fixed pore fluid pressure distribution, geologists have documented fault valving behavior, that is, cyclic changes in pressure and unsteady fluid migration along faults. Here we quantify fault valving through 2-D antiplane shear simulations of earthquake sequences on a strike-slip fault with rate-and-state friction, upward Darcy flow along a permeable fault zone, and permeability evolution. Fluid overpressure develops during the interseismic period, when healing/sealing reduces fault permeability, and is released after earthquakes enhance permeability. Coupling between fluid flow, permeability and pressure evolution, and slip produces fluid-driven aseismic slip near the base of the seismogenic zone and earthquake swarms within the seismogenic zone, as ascending fluids pressurize and weaken the fault. This model might explain observations of late interseismic fault unlocking, slow slip and creep transients, swarm seismicity, and rapid pressure/stress transmission in induced seismicity sequences.

Effect of Porosity and Permeability Evolution on Injection‐Induced Aseismic Slip

“…There could be cases where permeability increases due to pore connectivity enhancement without an actual increase in porosity, as captured through the tortuosity parameter in the Kozeny‐Carman relation (Bernabé et al., 2003). Some recent studies focus on this limit, and couple permeability with both effective normal stress and slip while neglecting changes in porosity and storage (Miller, 2020; Zhu et al., 2020). Furthermore, the power‐law relation between porosity and permeability used in this study also does not have a fixed exponent for all processes and rock types (David et al., 1994), nor is it even clear if a power‐law relation is relevant in all cases.…”

The Mechanics of Creep, Slow Slip Events, and Earthquakes in Mixed Brittle‐Ductile Fault Zones

“…Li & Liu, 2016;Liu, 2005Liu, , 2014Liu & Rice, 2007Matsuzawa et al, 2010;D. M. Saffer & Wallace, 2015;Segall & Bradley, 2012;Shibazaki et al, 2010;Skarbek et al, 2012;Veveakis et al, 2014;Zhu et al, 2020). SSEs are also modeled with a rate-and state formulation incorporating additional mechanism: (1) velocity-strengthening friction with increasing slip rates (Leeman et al, 2016;Shibazaki & Shimamoto, 2007), geometric complexities and roughness (D. Li & Liu, 2016;Romanet et al, 2018), decreases in pore fluid pressure due to shear-induced dilatancy (e.g., Marone et al, 1990;Segall et al, 2010).…”

“…Multiple constitutive behaviors have been proposed to explain how and why faults creep stably, deform metastably in slow slip events (SSEs) or slip unstably in earthquakes. Rate and state friction (RSF) laws are commonly used to explain variations in slip behavior, with some studies incorporating the mechanical effects of high pore fluid pressure or dehydration reactions (Dal Zilio et al., 2020; Gao & Wang, 2017; D. Li & Liu, 2016; Liu, 2005, 2014; Liu & Rice, 2007, 2009; Matsuzawa et al., 2010; D. M. Saffer & Wallace, 2015; Segall & Bradley, 2012; Shibazaki et al., 2010; Skarbek et al., 2012; Veveakis et al., 2014; Zhu et al., 2020). SSEs are also modeled with a rate‐ and state formulation incorporating additional mechanism: (1) velocity‐strengthening friction with increasing slip rates (Leeman et al., 2016; Shibazaki & Shimamoto, 2007), geometric complexities and roughness (D. Li & Liu, 2016; Romanet et al., 2018), decreases in pore fluid pressure due to shear‐induced dilatancy (e.g., Marone et al., 1990; Segall et al., 2010).…”

Episodicity and Migration of Low Frequency Earthquakes modeled with Fast Fluid Pressure Transients in the Permeable Subduction Interface

“…Here, we explore the potential of pressure transients in a permeable subduction interface to generate this type of activity. The structure and hydraulics of such a channel have rarely been studied in relation to seismicity [5,26,83,102]. We investigate the behaviour of a heterogeneous channel containing plugs of low permeability.…”