SCEC Award Number 23203 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Exploring sedimentation effects on pore-pressure conditions within the Salton Trough
Investigator(s)
Name Organization
Michael Oskin University of California, Davis
Other Participants
SCEC Priorities 2c, 3f, 5e SCEC Groups Geology, FARM, Seismology
Report Due Date 03/15/2024 Date Report Submitted 11/12/2024
Project Abstract
 Pore-pressure is a first-order control on fault stress conditions and earthquake triggering. High heat flow and overpressure conditions due to rapid sedimentation are hypothesized to affect fault behavior within the Salton Trough by promoting fault creep and earthquake swarms. To model the nonlinear coupled effects of sedimentation, compaction, and fluid flow we developed a Python-based implementation of the one-dimensional basin model of Bethke and Corbet (1988). We use the fluvial, marine, deltaic, and lacustrine sediments exposed in the Salton Trough as model inputs, and explore the impact of stratigraphic order and sedimentation rates over time. We find that overpressure readily develops within the lowermost basin sediments, beneath low permeability facies like delta front shale and silt from the Colorado River. Low permeability mudstones act as caprocks creating confined aquifers in the sand layers below them. Elevated pore pressure at depth occurs below these units and approaches lithostatic pressure more readily than when caprocks are absent. Three important outcomes of these models are: 1) within the actively subsiding Salton Trough, the ratio of pore pressure to lithostatic load (λ ) is probably everywhere ≥0.6 below 500 – 1000m depth, due to the combination of lower-density porous sediment and excess pore pressure developed beneath fine grained lacustrine and marine strata. 2) Overpressure conditions are likely present and could promote fault creep in the Salton Trough. Our modeled sediment columns show significant excess pore fluid pressure developing at above 4 km depth where faults have been observed to creep.
Intellectual Merit Pore-pressure is a first-order control on fault stress conditions and earthquake triggering. Overpressure conditions due to rapid sedimentation are hypothesized to affect fault behavior within the Salton Trough by promoting fault creep and earthquake swarms. We developed a numerical model to explore this problem using realistic sediment type, deposition rate, and thickness from he Salton Trough. We show that while the rapid sedimentation rate within the Salton Trough does promote overpressure in fine-grained sandy strata, the presence of less permeable shale and mudstone caprock units is essential for maximizing that overpressure and maintaining it over time.
Broader Impacts Seismicity in the Salton Trough has important implications for geologic hazard in southern California, including the southern terminus of the San Andreas fault. Anthropogenic and natural fluid-mediated effects on seismicity associated with geothermal energy are of direct societal concern for earthquake forecasting and hazard. Understanding the natural, in-situ pore-pressure conditions at seismogenic depth is essential to properly model these processes. This project supported a finishing Ph.D. student at UC Davis.
Exemplary Figure Figure 3. Plots showing how excess hydraulic head, pore pressure ratio, hydraulic conductivity, and porosity vary with depth for 3 different stratigraphic columns using our 1D model. Top: Simplified version of the FCVB stratigraphy. Middle: Stratigraphy in the modern Salton Trough (Babcock, 1974; Randall 1974) compared with all fine sand column. Bottom: Excess hydraulic head with depth for all three stratigraphic columns after 5 Myr period of slow deposition.
Linked Publications

Add missing publication or edit citation shown. Enter the SCEC project ID to link publication.