Mechanical properties of the seismogenic zone

Open Access
Author:
Scuderi, Marco Maria
Graduate Program:
Geosciences
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 12, 2014
Committee Members:
  • Chris J Marone, Dissertation Advisor
  • Chris Marone, Committee Chair
  • Demian Saffer, Committee Member
  • Derek Elsworth, Committee Member
  • Peter Christopher Lafemina, Committee Member
  • Eliza Richardson Marone, Committee Member
Keywords:
  • earthquakes
  • friction
  • granular physics
Abstract:
Understanding the processes that dictate the evolution of frictional strength during the seismic cycle is a central problem in characterizing the seismic potential of faults and in relating earthquake source parameters such as stress drop to recurrence interval and geologic and geodetic fault slip rates. Laboratory friction experiments provide insight into the mechanisms of fault healing, and results of these studies provide the fundamental underpinnings of the rate- and state-friction laws. Frictional healing is the mechanism(s) associated with fault restrengthening following failure, where time-, slip- and velocity- dependent processes dictate the evolution of real contact area at grain junctions within fault gouge. The objective of this work is to illuminate the micromechanics of frictional healing and the relation between mechanical and hydraulic properties of fault gouge. Four main dissertation chapters are combined with three additional collaborative works describing research on the fundamental processes that govern earthquakes and tectonic faulting. Chapter one is focused on the role of water during repetitive stick- slip frictional sliding, with particular emphasis on the grain scale mechanisms of frictional restrengthening. A micromechanical model for gouge deformation is developed, based on the interpretation of mechanical and microstructural observations. Chapter two describes the role of pore fluid pressure during earthquake nucleation and dynamic rupture. Experiments were performed on synthetic granular fault gouge under a range of hydrological boundary conditions from drained to undrained. The experiments demonstrate that when gouge layers are deformed under undrained boundary conditions, time-dependent strengthening and the magnitude of stress drop increase, when compared with drained conditions. I conclude that under undrained conditions, a series of feedback processes between pore fluid depressurization and stress enhanced pressure solution creep control time-dependent elasto-plastic deformation at frictional contacts. These observations have important implications for models of earthquake recurrence and for theoretical models of granular deformation. Chapter three was designed to investigate the relation between permeability and porosity across the brittle ductile transition in siliciclastic rocks, with implication for the up-dip limit of seismo-genesis along subduction zones. I find that permeability is dependent on the deformation style and strain localization. In the brittle regime shear localization along discrete bands can act as a barrier to fluid flow, modifying the hydrological properties and distribution of fluids. The possible generation of overpressures can lower the effective stress surrounding the shear plane and thus favor the nucleation/propagation of earthquake rupture. Chapter four describes work to examine the frictional stability and hydrological properties of natural serpentinite samples from the San Andreas Fault in central California. The aim of this work was to shed light on the deformation mechanism(s) responsible for the spectrum of fault slip behaviors, including Low Frequency Earthquakes (LFE), slow earthquakes, and non volcanic tremor. I find that when serpentinite is associated with other weak phyllosilicates minerals (i.e. talc), for typical seismogenic depths, it can control the mode of fault failure showing the potential characteristics for generating LFE and other forms of transient slip.