Investigations of Earthquake Source Processes Based on Fault Models with Variable Friction Rheology

Citation

Kaneko, Yoshihiro (2009) Investigations of Earthquake Source Processes Based on Fault Models with Variable Friction Rheology. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/1WGT-6623. https://resolver.caltech.edu/CaltechETD:etd-04282009-202026

Abstract

Ample experimental and observational evidence suggests that friction properties on natural faults vary spatially. In the lab, rock friction depends on temperature and confining pressure and it can be either velocity weakening or velocity strengthening, leading to either unstable or stable slip. Such variations in friction rheology can explain patterns of seismic and aseismic fault slip inferred from field observations.

This thesis studies earthquake source processes using models with relatively simple but conceptually important patterns of velocity-weakening and velocity-strengthening friction that can arise on natural faults. Based on numerical and analytical modeling, we explore the consequences of such patterns for earthquake sequences, interseismic coupling, earthquake nucleation processes, aftershock occurrence, peak ground motion in the vicinity of active faults, and seismic slip budget at shallow depths. The velocity-dependence of friction is embedded into the framework of logarithmic rate and state friction laws.

In addition to using existing boundary integral methods, which are accurate and efficient in simulating slip on planar faults embedded in homogeneous elastic media, the thesis develops spectral element methods to consider single dynamic ruptures and long-term histories of seismic and aseismic slip in models with layered bulk properties.

The results of this thesis help to understand a number of observed fault slip phenomena, such as variability in earthquake patterns and its relation to interseismic coupling, seismic quiescence following decay of aftershocks at inferred rheological transitions, instances of poor correlation between static stress changes and aftershock occurrence, the lack of universally observed supershear rupture near the free surface, and coseismic slip deficit of large strike-slip earthquakes at shallow depths. The models, approaches, and numerical methods developed in the thesis motivate and enable consideration of many other earthquake source problems, such as the combined effect of two or more triggering mechanisms on aftershock rates, inferring friction properties on natural faults based on seismic and geodetic measurements, seismic hazard assessment based on observed interseismic coupling, and the effect of heterogeneous and/or nonelastic bulk properties on earthquake sequences.

Thesis Files