Great Valley fault system

Great Valley fault system
Name	Great Valley fault system
Country	United States
State	California
Region	Central Valley
Length	~400 km
Type	strike-slip, thrust, normal components
Coordinates	36°N 120°W

Great Valley fault system The Great Valley fault system is a network of active and potentially active fault zones beneath California’s inland Central Valley, linking coastal and Sierra Nevada structures. The system interacts with the San Andreas Fault, Hayward Fault, Garlock Fault, and Sierra Nevada frontal faults, influencing seismic hazards for Sacramento, Fresno, Stockton, and Bakersfield. It has been the subject of investigations by institutions such as the United States Geological Survey, California Geological Survey, and universities including Stanford University and the University of California, Berkeley.

Overview

The Great Valley fault system spans much of the Central Valley, connecting structural elements near the Coast Ranges and the Sierra Nevada. It comprises suites of buried strike-slip, thrust, and normal faults that have been mapped using seismic reflection, aeromagnetic survey, and gravimetry studies by agencies like the U.S. Army Corps of Engineers and research groups from California Institute of Technology. The system affects groundwater basins monitored by the California Department of Water Resources and infrastructure corridors used by Union Pacific Railroad and Interstate 5.

Geology and Tectonics

Geodetically, the fault system lies within the Pacific–North American plate boundary zone that also hosts the San Andreas Fault system and the Mendocino Triple Junction. Structural evolution is tied to Mesozoic accretionary processes that built the Sierra Nevada batholith and Late Cenozoic deformation associated with the Farallon Plate subduction and rifting episodes recorded near the Eocene and Miocene stratigraphic units. Strike-slip motion on buried strands links to regional folds such as the Coalinga Anticline and thrusts adjoining the Kern River Oil Field and Sacramento Valley petroleum provinces explored by companies like Chevron and Shell Oil Company.

Fault Architecture and Segmentation

The architecture comprises multiple en echelon strands with segmentation similar to the Calaveras Fault and Elsinore Fault Zone, with discrete segments beneath alluvial cover imaged in reflection seismology profiles. Major mapped segments trend NW–SE and link to splays near the Temblor Range and the San Joaquin Valley. Junctions with the Garlock Fault and cross faults mirror complexities seen at the Loma Prieta rupture termination and the 1992 Landers earthquake rupture network. Fault zone heterogeneity controls rupture propagation and slip partitioning beneath features such as the Kettleman Hills and Avenal Gap.

Seismic History and Paleoseismology

Instrumental seismicity within the valley has been lower than along coastal faults, but historic events recorded by the USGS National Seismic Network and catalogs include seismic swarms and moderate earthquakes that align with mapped structures. Paleoseismic trenching near buried scarps and radiocarbon-dated stratigraphic offsets ties rupture episodes to Holocene earthquakes, comparable in recurrence discussion to the 1906 San Francisco earthquake and the 1857 Fort Tejon earthquake on adjacent fault systems. Studies published through Seismological Society of America journals and by research teams at the Scripps Institution of Oceanography have refined timing for prehistoric ruptures affecting fluvial terraces along the San Joaquin River.

Hazard Assessment and Risk Mitigation

Hazard models from the United States Geological Survey and the California Earthquake Authority incorporate potential ruptures within the fault system into regional probabilistic seismic hazard assessments that inform building codes administered by the California Building Standards Commission and retrofitting programs by the Federal Emergency Management Agency. Lifelines such as California State Route 99, California Aqueduct, and power transmission corridors owned by Pacific Gas and Electric Company are assessed for fault-related shaking, surface rupture, and liquefaction, guided by National Research Council recommendations and FEMA P-154 guidance. Urban planners in Modesto and Merced include scenario modeling derived from studies at Los Alamos National Laboratory and university consortia.

Monitoring and Research

Monitoring leverages dense networks: the California Integrated Seismic Network, continuous Global Positioning System stations of the Plate Boundary Observatory, and interferometric synthetic aperture radar products developed by NASA and Jet Propulsion Laboratory. Research collaborations among USGS, UC Davis, and Caltech apply 3D seismic tomography, borehole logging, and sediment core analysis to map blind faults and constrain stress accumulation. Citizen science platforms and state-funded initiatives complement long-term paleoseismic trenching led by geologists such as those from the California Geological Survey.

Human and Environmental Impacts

Seismic activity and fault-zone deformation influence agriculture in the San Joaquin Valley, oil and gas operations in the Kern County fields, and urban development patterns in Stockton and Bakersfield. Ground shaking exacerbates land subsidence already driven by groundwater extraction regulated by the Sustainable Groundwater Management Act and overseen by local agencies like the Tulare Lake Basin Groundwater Sustainability Agency. Emergency response planning by California Office of Emergency Services and public health preparedness by the California Department of Public Health incorporate scenarios for infrastructure disruption, transportation interruption affecting Port of Stockton access, and ecosystem impacts in wetlands managed by California Department of Fish and Wildlife.

Category:Geology of California Category:Seismic zones of the United States