The influence of depth-dependent fault rock permeability and shear zone width on variability in earthquake rupture and arrest depths

Junle Jiang

In Preparation October 30, 2022, SCEC Contribution #12629

The spatial variability and depth extent of fault slip during large earthquakes are important factors that affect seismic hazard, but their physical controls remain unclear. Here we use numerical simulations of crustal strike-slip faults in three dimensions (3-D) to explore how dynamic rupture processes and fault zone properties influence the rupture development, arrest depths, and slip patterns of large earthquakes. Our fault zone models incorporate depth-dependent properties of quasi-static rate-and-state friction and dynamic fault weakening mechanisms, including flash heating of microscopic frictional contacts and thermal pressurization of pore fluids. The efficiency of coseismic shear heating due to thermal pressurization, as determined by the competition between permeability and width of the shear zone, decreases with depth at the base of the seismogenic layer. In our models with plausible values of hydraulic diffusivity and shear zone width, earthquake slip can penetrate into deeper fault extensions by a few km, depending on the earthquake size. The along-depth behavior of large events affects their along-strike development due to the positive feedback loop between dynamic properties of rupture and enhanced dynamic weakening, despite uniform fault properties along the strike. The non-uniform slip during one event leads to spatial-temporal complexity in subsequent events, including large variations of depth extent with time. In these simulations, the maximum downdip penetration distance is linearly proportional to maximum earthquake slip, while the overall stress drop only slightly increases with size due to stress increase in deeper slipping regions. We find that simulations of 2-D antiplane models always produce larger earthquake size and deeper slip, partly due to fewer earthquake nucleation sites. Simple theoretical considerations explain that the maximum coseismic rupture depths in different models coincide with sub-meter-scale widths of deeper shear zones. While large uncertainties about fault zone properties still exist, such physics-based simulations can integrate new laboratory and field observations to better understand large earthquake behavior.

Key Words
Dynamic rupture, earthquake sequence, friction laws, thermal pressurization, flash heating, hydraulic diffusivity, permeability, shear zone, seismic-aseismic transition

Citation
Jiang, J. (2022). The influence of depth-dependent fault rock permeability and shear zone width on variability in earthquake rupture and arrest depths. Tectonophysics, (in preparation).

Related Projects & Working Groups
SEAS, Fault and Rupture Mechanics (FARM)