Research

Our research is focused on the physics of earthquakes and faulting and the mechanics of frictional sliding.  Activities include laboratory experiments, analysis of field data, and numerical studies of faulting and dynamic rupture.  Our laboratory work is focused on frictional and rheologic properties of brittle materials.  The goal of this work is to develop a set of friction constitutive laws to describe the rheology of brittle deformation.  A key part of the laboratory work has been identifying and documenting the effects of dilatancy and shear localization on second order variations in friction.  We also devote significant effort to the scaling problems inherent in applying laboratory data to seismogenic faults.  Connecting laboratory observations to field data and theoretical studies is a critical part of modern experimental studies.
 

Laboratory

Critical Slip Distance: Discovery that the critical slip distance for seismic faulting (the slip over which strength breaks down and thus a fundamental parameter controlling the stability of faulting) scales with shear strain in fault zones and is best envisaged as a critical shear strain within zones of high strain rate (Marone & Kilgore, 1993).  This work led to a new micromechanical model for the critical slip distance (Marone and Kilgore, 1993; Marone and Cox, 1994; Karner and Marone, 1998; Mair and Marone, 1999; Richardson and Marone, 1999; Sleep et al., 2000).

Equivalence of Static and Dynamic Friction: 1) Explanation of the relationship between time-dependent static aging and velocity-dependent sliding friction (Marone, 1998a, 1998b).  2) Identification of the loading rate effect on static friction and aging (Marone 1997, 1998a).  This work derives from detailed analysis of aging and frictional healing in granular material at high pressure, and critical reassessment of the slip-rate and state-variable friction laws (Marone, 1997, Karner et al., 1997, Marone 1998a,b, Karner and Marone, 1998, 2001, Richardson and Marone, 1999).

Friction-Porosity Relationship: Discovery of the role of dilatancy in controlling 2nd-order friction characteristics including memory effects and velocity dependence of sliding friction (Marone and Scholz, 1989, Marone et al., 1990, Marone, 1991; Karner and Marone, 1998; Richardson and Marone, 1999; Mair and Marone, 1999).  Interpretation of the friction state variable in terms of porosity in fault gouge (Marone, 1998a, 1998b, Marone et al., 1990).

 
Fault Healing: Analysis of repeating earthquakes leading to the first reliable seismic estimates of the rate of fault healing (Marone et al., 1995). Explanation of the apparent discrepancy between the rate of fault healing and laboratory measurements of the rate of frictional aging (Marone et al., 1995, Karner et al., 1997, Marone 1997, 1998a, 1998b).

Afterslip:  Development of a physically-based model for earthquake afterslip and shallow post-seismic deformation (Marone et al., 1991).  Depth of Seismic Faulting:  Explanation of shallow aseismic slip and the upper stability transition on mature faults (Marone and Scholz, 1988).  Field and laboratory-based studies leading to a self-consistent model for the effect of sediments and fault gouge on the seismic and aseismic behavior of crustal faults and subduction zone accretionary prisms (Marone and Scholz, 1988; Marone et al., 1990; Marone et al, 1991).

Earthquake Nucleation: Modeling of earthquake nucleation using quantitative definitions of the transitions from quasi-static to dynamic slip, laboratory-derived friction laws, and inertial effects as related to fault zone width (Roy and Marone, 1996).
 

Mechanics of the critical slip distance and application of laboratory data to seismic faulting

The rate of fault healing and implications for friction constitutive laws

Numerical studies of earthquake nucleation and dynamic rupture propagation

Numerical modeling of friction data and inversion for friction constitutive parameters

Upper stability transition on mature faults and the mechanics of earthquake afterslip

Frictional behavior of smectite and illite-rich clay gouges with application to the mechanics of subduction zone megathursts

Influence of grain characteristics on the friction of granular shear zones

The effect of humidity on granular friction

Creep and frictional behavior of laboratory fault zones subject to time-dependent fluctuations of normal and shear load

Friction and shear heating at high velocity

Effect of shear load, including true stationary contact, on frictional healing

Effect on frictional healing of loading rate and accumulated displacement