Santa Susana Fault

Santa Susana Fault The Santa Susana Fault is a northwest-trending active fault zone in Southern California that traverses the Simi Valley, San Fernando Valley margins and the Santa Susana Mountains. It has been the focus of geological, seismological and engineering studies by agencies such as the United States Geological Survey and the California Geological Survey, and has implications for regional infrastructure owned by entities including the Metropolitan Water District of Southern California and the Southern California Edison Company. The fault interacts with nearby structures studied in works by universities such as the California Institute of Technology and the University of California, Los Angeles.

Geology and Fault Characteristics

The fault exhibits predominantly right-lateral strike-slip motion with a reverse-oblique component, recorded in mapping by the United States Geological Survey, the California Division of Mines and Geology, and academic teams from the University of Southern California and the University of California, Berkeley. Exposed in outcrops within the Santa Susana Mountains and along the northern margins of the San Fernando Valley, the zone juxtaposes Tertiary sedimentary units like the Modelo Formation and Mesozoic crystalline rocks of the Sierra Pelona-adjacent terranes. Structural analyses reference techniques developed at the Scripps Institution of Oceanography and isotopic dating methods refined at the Lawrence Livermore National Laboratory and the United States Geological Survey laboratories. Fault gouge, slickenlines and uplifted fluvial terraces documented in reports from the Los Angeles County Museum of Natural History and the Natural History Museum of Los Angeles County inform kinematic interpretations used in models produced by research groups at the Jet Propulsion Laboratory and the Southern California Earthquake Center.

Seismology and Earthquake History

Instrumental and paleoseismic investigations link the fault to Holocene surface-rupturing events identified by trenching studies overseen by the United States Geological Survey, the California Geological Survey, and teams from the University of California, Davis and California State University, Northridge. Historical seismicity in the region includes impacts from the 1906 San Francisco earthquake-era stress field studies and later cataloging by the National Earthquake Information Center. Seismic reflection profiles and paleoseismology described in publications by the Seismological Society of America and the American Geophysical Union place constraints on recurrence intervals comparable to those reported for nearby faults like the San Andreas Fault, the Northridge Blind Thrust, and the San Gabriel Fault. Ground-motion modeling used by the Federal Emergency Management Agency and the California Office of Emergency Services incorporates data from networks operated by the Southern California Seismic Network and instrumentation developed at the Caltech Seismological Laboratory.

Tectonic Setting and Regional Fault Network

The fault lies within the complex transtensional and transpressive plate-boundary region influenced by the relative motion of the Pacific Plate and the North American Plate, with strain partitioning across structures including the San Andreas Fault system, the Transverse Ranges, and the Transverse Ranges province faults. It forms part of a web of crustal discontinuities interacting with the Sierra Madre Fault Zone, the Chatsworth Reservoir area structures, and subsidiary splays that connect to the Oak Ridge Fault and the Verdugo Fault. Regional tectonic syntheses by the USGS National Seismic Hazard Model and contributions from researchers at the Paleoseismology Laboratory at Oregon State University and the Institute of Geological and Nuclear Sciences inform how the fault transfers slip to the broader Southern California fault network, with comparisons to crustal deformation studies from the European Plate and the Alpine Fault used in analog modeling.

Hazard Assessment and Risk Mitigation

Hazard assessments conducted by the California Geological Survey, the United States Geological Survey, and county emergency planners evaluate surface-rupture potential, peak ground acceleration, and liquefaction susceptibility for infrastructure such as Interstate I-5, Interstate 210, and municipal water conveyance systems operated by the Los Angeles Department of Water and Power. Urban planning and building-code implications have been incorporated into updates by the California Building Standards Commission and enforced through ordinances from the Los Angeles County Department of Public Works and local city governments including Thousand Oaks, Simi Valley and Chatsworth. Mitigation strategies draw on guidelines from the Federal Emergency Management Agency, retrofitting programs promoted by the California Earthquake Authority, and community preparedness efforts run by the American Red Cross and the Los Angeles County Office of Emergency Management.

History of Investigation and Monitoring

Geological reconnaissance began with 20th-century mapping by the U.S. Geological Survey and academic surveys from institutions such as the California Institute of Technology and University of Southern California. Paleoseismic trenching campaigns and stratigraphic studies were conducted by teams affiliated with the California Division of Mines and Geology, the United States Geological Survey, and universities including California State University, Northridge and California State University, Los Angeles. Continuous and temporary seismic instruments have been deployed by the Southern California Seismic Network, the Caltech Seismological Laboratory, and the USGS Earthquake Hazards Program, while remote-sensing and InSAR analyses have been produced by the Jet Propulsion Laboratory and the National Aeronautics and Space Administration. Peer-reviewed findings have appeared in journals published by the Seismological Society of America, the American Geophysical Union, and university presses at institutions such as the University of California Press.

Category:Geology of Los Angeles County, California Category:Seismic faults of California