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| San Manuel Fault | |
|---|---|
| Name | San Manuel Fault |
| Location | Southern California, United States |
| Length | ~20–30 km |
| Type | Strike-slip / oblique-slip |
| Tectonic setting | Transverse Ranges, San Andreas Fault system |
San Manuel Fault The San Manuel Fault is a geological fault zone in southern California associated with oblique-slip motion within the Transverse Ranges near the San Gabriel Mountains and the Mojave Desert. The fault lies within the broader San Andreas Fault system and interacts with nearby structures such as the Sierra Madre Fault, Cucamonga Fault, and San Jose‑Hondo Fault, contributing to regional seismicity and landscape evolution. It has been the subject of investigations by institutions including the United States Geological Survey, California Geological Survey, and several universities.
The San Manuel Fault is mapped in the vicinity of San Bernardino County, California, near communities such as Victorville, California, Upland, California, and San Bernardino, California, and is spatially associated with features including the San Gabriel Mountains (California), Mojave Desert, and the Los Angeles Basin. Regional studies by agencies like the United States Geological Survey and the California Geological Survey place it within fault networks that include the San Andreas Fault, San Jacinto Fault Zone, and the Elsinore Fault Zone. Historical mapping campaigns by researchers from the California Institute of Technology, University of California, Los Angeles, and University of Southern California have refined its trace, geometry, and slip rates.
The fault displays strike‑slip and oblique components typical of structures within the Transverse Ranges (California), with lithologies along the trace including crystalline basement rocks of the San Gabriel Mountains and sedimentary cover sequences of the Pacific Plate margin. Structural studies reference cross‑cutting relations with the Garlock Fault and folding related to the Peninsular Ranges Batholith and basin deposits of the Los Angeles Basin. Geologists correlate geomorphic markers such as offset alluvial fans, river channel deflections, and uplifted terraces with stratigraphic units recognized in mapping by the California Division of Mines and Geology and academic monographs from the Seismological Society of America.
Seismic records from institutions like the Southern California Seismic Network, United States Geological Survey, and archived catalogs show localized seismicity near the San Manuel Fault, with associations to historically significant events such as the 1857 Fort Tejon earthquake on the San Andreas Fault and the 1971 San Fernando earthquake in the Transverse Ranges. Paleoseismic investigations, trenching studies, and radiocarbon dating by teams from USGS and universities have sought evidence for Holocene surface rupture, recurrence intervals, and paleo‑ground motions comparable to ruptures documented on the San Jacinto Fault and El Mayor–Cucapah earthquake (2010). Seismologists compare instrumental records with analogs from the 1992 Landers earthquake and the 1994 Northridge earthquake to assess slip potential.
The San Manuel Fault resides within the complex plate boundary between the Pacific Plate and the North American Plate, interacting with major structures including the San Andreas Fault, San Jacinto Fault Zone, and the Garlock Fault. Regional tectonics governed by right‑lateral shear of the Pacific Plate relative to the North American Plate has produced the east‑west trending Transverse Ranges (California) and transverse fault linkages seen in fault maps produced by the USGS and academic consortia from Caltech and UCLA. Tectonic reconstructions reference Neogene deformation recorded in the Mojave Desert basins, the Santa Monica Mountains, and the Peninsular Ranges.
Hazard assessments conducted by the California Earthquake Authority, Federal Emergency Management Agency, and regional planners consider the San Manuel Fault in context with neighboring sources such as the San Andreas Fault and San Jacinto Fault, evaluating ground‑motion scenarios, liquefaction potential in basin deposits like those in the Los Angeles Basin, and infrastructure vulnerability for corridors including Interstate 10 in California and Interstate 15. Mitigation measures advocated by agencies such as the California Office of Emergency Services include updated building codes influenced by the 1971 San Fernando earthquake and the 1994 Northridge earthquake, land use planning informed by maps from the California Geological Survey, and public preparedness programs promoted by the FEMA and local governments of San Bernardino County, California and nearby cities.
Ongoing research involves seismic monitoring by the Southern California Seismic Network, geodetic measurements using Global Positioning System networks supported by institutions such as Scripps Institution of Oceanography and Jet Propulsion Laboratory, and geological field studies by faculty and students at California Institute of Technology, University of California, Los Angeles, and University of Southern California. Collaborative projects funded by agencies like the National Science Foundation and the United States Geological Survey employ LiDAR mapping, trenching, and GPS time‑series analysis to refine slip rates, rupture potentials, and interactions with faults such as the Cucamonga Fault and Sierra Madre Fault Zone. Results inform probabilistic seismic hazard models used by the USGS and the California Earthquake Authority.