JavaScript is disabled for your browser. Some features of this site may not work without it.
Estimation of permeability, porosity, and grain-size distributions across the San Andreas Fault Zone in northwest Coachella Valley, California (Riverside County)
The groundwater aquifer system in the northwestern region of Coachella Valley,
California serves as a major natural resource for agricultural and municipal uses. In this
region, the aquifer system is partitioned into four groundwater sub-basins due to the
presence of the San Andreas fault zone. Previous investigation involving land surface
deformation, seismic data, and groundwater data indicate there are at least three main
strands of the San Andreas Fault- Mission Creek Strand, Banning Strand, and Garnet Hill
Strand. For years, these faults have been characterized as simple barriers to fluid flow due
to measureable offsets in the water table across the fault strands and hydrochemistry
variations. The ability for a fault to act as a barrier to flow in an aquifer system is the
result of significant development of gouge causing lateral variations in fault zone
permeability but the mechanisms for gouge development in the Coachella Valley in
unconsolidated-to-weakly consolidated sediments is unclear. Another explanation for
variations in water chemistry, temperature, and groundwater levels is due to displacement
of impermeable bedrock or relative offset of water bearing units. This study proposes to
document variations of permeability and porosity across the San Andreas Fault zone.
Field mapping, sampling and descriptions of fault zone, damage zone, and gouge width
were recorded at four fault outcrop locations in the region. Analysis of porosity,
hydraulic conductivity, intrinsic permeability, and grain size distribution across the fault
zone associated with each fault strand indicate that different regions of the fault zone can xiii
act to impede and/or enhance fluid flow across the faults. This data analysis of
permeability and porosity variations across fault zones will help develop a better
understanding of fault and aquifer interactions for future groundwater models, recharge
activities, fault displacement, and development of gouge in unconsolidated sediments.
Description:
Includes bibliographical references (pages 115-118)
California State University, Northridge. Department of Geological Sciences.