Subduction Zone Tectonics & Fault Mechanics: Our studies of subduction zone tectonics, faulting, and earthquake behavior include numerical modeling studies of fluid flow, participation in NanTroSEIZE (a major scientific Ocean Drilling field Program), work on a 3-D seismic reflection survey, and laboratory experiments to measure permeability and geotechnical properties of sediment.

Fluids and the San Andreas Fault: Our work on the San Andreas Fault system focuses on three main topics. First, we are using a combination of numerical modeling and analysis of heat flow data to understand the thermal state of the crust and to constrain mechanisms of heat transport in the vicinity of the fault. Second, we are investigating hypothesized mechanisms for generation of elevated fluid pressures within the fault zone and surrounding crust, as one possible explanation for a mechanically weak fault. Third, we are conducting a suite of laboratory measurements to characterize the frictional and hydrologic properties of material sampled from outcrop and the SAFOD borehole.

Regional Hydrology: Our studies of regional hydrogeology include investigating the fate and transport of waters co-produced with coal bed methane, detailed study of hydraulic properties and recharge in a fractured regional aquifer system, and laboratory measurements of permeability reduction caused by deformation bands in porous sandstone aquifers and reservoirs.

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).

Field Applications and Theoretical Studies
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).