Inglewood Fault Zone

Inglewood Fault Zone
Name	Inglewood Fault Zone
Location	Los Angeles County, California, United States
Length	~18–25 km
Plate	North American Plate
Type	Right-lateral strike-slip with reverse component
Status	Active
Coordinates	33.94°N 118.35°W

Inglewood Fault Zone is a shallow, active strike-slip fault system in southwestern Los Angeles County, California, crossing densely urbanized parts of the Los Angeles Basin near Inglewood, California and LAX. The zone has been investigated by agencies such as the United States Geological Survey and the California Geological Survey because of its proximity to infrastructure including Los Angeles International Airport, the Century City complex, and the San Pedro Bay ports. Studies have involved institutions like the California Institute of Technology, the University of California, Los Angeles, and the Southern California Earthquake Center.

Geology and Structure

The fault zone lies within the broader structural framework of the Transverse Ranges and the Peninsular Ranges junction, juxtaposed against sedimentary strata of the Santa Monica Mountains foothills and the Los Angeles Basin syncline. Lithologies include the Repetto Formation, the Fernando Formation (now often correlated with the Repetto Member), and Quaternary alluvium derived from the San Gabriel Mountains. Crosscutting relationships with the Palos Verdes Fault and splays related to the San Andreas Fault system indicate a complex kinematic partitioning between right-lateral strike-slip motion and reverse dip-slip shortening. Geophysical surveys using seismic reflection profiles and borehole logs have imaged blind strands that step over near the Ballona Creek and Dominguez Channel alignments.

Seismicity and Earthquake History

Instrumental seismicity recorded by the Southern California Seismic Network and catalogs maintained by the United States Geological Survey show microseismic clusters beneath the fault zone, with focal mechanisms consistent with right-lateral motion and modest reverse component. Paleoseismic trenching performed by teams from the California Geological Survey and USGS near the LAX complex has sought evidence for Holocene ruptures similar in character to events on the Newport–Inglewood Fault. Historic earthquakes felt in the region, recorded in accounts archived by the Los Angeles Times and cataloged by the National Earthquake Information Center, include shaking episodes correlated spatially with the zone though unambiguous surface ruptures are rare compared with events on the San Jacinto Fault or the Garlock Fault.

Geomorphology and Surface Expression

Surface expression is subtle in much of the urbanized corridor, with geomorphic features such as linear alignments, sag ponds, and offset stream channels observable along remnant alluvial surfaces of Ballona Creek and paleochannels feeding Ballona Wetlands. Shoreline-cliff deformation near Dockweiler State Beach and structural controls on depositional lobes in Dominguez Channel deltaic plains reflect long-term activity. Remote sensing analyses combining LiDAR, high-resolution aerial photography from NASA missions, and paleochannel mapping by the United States Geological Survey reveal en echelon fault traces, right-stepping bends, and localized uplift near the Mott Street–Florence Avenue corridor.

Tectonic Setting and Regional Context

The fault zone is one of several active structures within the southern California plate boundary zone that redistribute slip transferred from the San Andreas Fault system into the Transverse Ranges and the Pacific Plate margin. Interactions with neighboring structures such as the Newport–Inglewood Fault, the Compton Fault, and splays tied to the Whittier Fault illustrate how strain is partitioned across the Los Angeles Basin’s network of faults. Regional stress orientations derived from focal mechanisms and GPS vectors from the Plate Boundary Observatory and the California GPS Network corroborate a predominantly northwest-directed shear regime with local transtensional to transpressional variations.

Monitoring and Instrumentation

Monitoring efforts include dense seismic arrays operated by the Southern California Seismic Network and near-surface geodetic stations supported by the United States Geological Survey and the California Institute of Technology. Downhole seismometers in municipal boreholes, strong-motion instruments deployed by the California Strong Motion Instrumentation Program, and continuous GPS sites managed by the Scripps Institution of Oceanography and UNAVCO provide constraints on microseismicity and crustal deformation. Geophysical campaigns using seismic reflection, magnetotelluric surveys, and shallow borehole stratigraphy have been conducted in collaboration with the University of Southern California and consulting firms engaged by Los Angeles World Airports.

Hazard Assessment and Mitigation

Hazard models prepared by the United States Geological Survey and the California Geological Survey incorporate probabilistic seismic hazard analyses that consider the fault zone’s slip rate, geometry, and recurrence parameters in scenarios affecting Los Angeles International Airport, major freeways such as the I-405 (California), and lifelines serving the Port of Los Angeles. Building retrofit programs influenced by California Senate Bill 1953 and mitigation guidelines from the Federal Emergency Management Agency and the California Office of Emergency Services address risks to hospitals, schools like the University of Southern California, and critical energy infrastructure. Urban resilience planning coordinated by the Los Angeles Mayor’s Office of Emergency Management and county agencies integrates scenarios from the HayWired-style projects and regional earthquake response exercises.

Land Use and Urban Impact Studies

Urban planning and environmental impact assessments by the Los Angeles County Department of Regional Planning and municipal agencies have evaluated development constraints, liquefaction potential in reclaimed areas near San Pedro Bay, and induced hazards from groundwater drawdown affecting subsidence patterns studied by the California Department of Water Resources. Transportation corridor studies by the Los Angeles County Metropolitan Transportation Authority and airport expansion reviews by Los Angeles World Airports include seismic vulnerability assessments tied to the fault zone. Community outreach and risk communication efforts involve partnerships with the American Red Cross, local school districts, and neighborhood councils across Inglewood, California, Hawthorne, California, and adjacent cities.

Category:Faults of California Category:Geology of Los Angeles County, California