SCEC Award Number 11145 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Earthquake Petrology: Deformational processes near the Brittle-Plastic Transition
Investigator(s)
Name Organization
James P. Evans Utah State University
Other Participants Mitchell Prante, Susanne Janecke, Rebekah Wood, Laurel Goodwin
SCEC Priorities A7, A8, A10 SCEC Groups FARM, LAD
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
We investigate the deformation mechanisms and slip processes at high temperature conditions, either in the presence of water [hydrothermal conditions] or at frictional heat melt conditions. At the intersection of the NNW-trending Elsinore fault and the inactive West Salton detachment fault we show that damage along the Elsinore ranges in thickness from a narrow slip plane to > 100 m along the eastern flank of the Tierra Blanca Mountains. Thermal fluids (~30°C) emerge at the intersection of the West Salton detachment and Elsinore faults actively alter the host rock, already fractured and crushed during fault slip. Fault cores contain thin chlorite ± epidote zones. The NW-striking West Salton detachment fault (WSDF) is a low-angle normal fault that formed and slipped at a low-angle (<30°). We document the presence of 0.1 cm to 2 m-thick, aphanitic, fault-related rocks. Microstructural and electron beam methods established a melt origin for these fault-rocks. In the cored rocks from the Cajon Pass, deformation and alteration of fault-related rocks adjacent to the steeply dipping Cleghorn fault span the brittle to semi-brittle deformational regime at hydrothermal conditions. Fault frequency increases with depth, and fracture densities are greater around fault zones. This fault correlates well with the left-lateral steeply dipping Cleghorn fault, and reflects the interaction between hydrothermal and deformation processes at depth. The data also show that damage zones are a long-lived presence of the deformed and altered zones of reduced elastic moduli associated with faults, and that semi-brittle distributed shearing may occur at depths as shallow as 3-4 km.
Intellectual Merit We investigate the deformation mechanisms and slip processes at high temperature conditions, either in the presence of water [hydrothermal conditions] or at frictional heat melt conditions. The data show that fluid-rock interaction damage zones associated with faults are common, with narrow slip surfaces and long-lived presence of the deformed and altered zones of reduced elastic moduli associated with faults, and that semi-brittle distributed shearing may occur at depths as shallow as 3-4 km in the region.
Broader Impacts This work has supported two graduate students [one PhD, one Msc] and served as a step off point for a 2011 SCEC intern project that provided a research project for four interns. The interns conducted field work, did laboratory work, analized and synthesized their data. The interns also presented results at national AGU and GSA meetings. We had two females and one hispanic intern, and the Msc student is a woman.
Exemplary Figure Figure 3.