EarthquakesinCaliforniatoday:liveseismicactivityacrossthestate

Length

1200 km

Max plausible

M8.2

Return period

~150 years on southern segment; ~200 years on northern segment

The San Andreas is a right-lateral transform boundary between the Pacific and North American plates running 1,200 km from the Salton Sea to offshore Cape Mendocino. The southern segment has not produced a major rupture since 1857, placing it roughly 170 years into a ~150-year recurrence cycle and making it the primary candidate for the next catastrophic California earthquake. Slip rates average 25–35 mm/year, and a full southern-segment rupture is expected to produce M8.0–8.2 shaking across the greater Los Angeles region.

Length

120 km

Max plausible

M7.0

Return period

~140–170 years; last major rupture 1868

The Hayward Fault runs beneath the densely populated East Bay cities of Oakland, Berkeley, Hayward, and Fremont, making it widely considered the most dangerous urban fault in the United States. It last produced a M6.8 earthquake in 1868 — now over 155 years ago — and USGS assigns a 33% probability of a M6.7+ rupture in the next 30 years. A major Hayward rupture would shake BART tunnels, the Bay Bridge anchorages, and tens of thousands of unreinforced masonry buildings in Oakland and Berkeley simultaneously.

Length

180 km

Max plausible

M7.5

Return period

~200–700 years per segment

The Elsinore Fault Zone is a northwest-trending right-lateral fault extending from the Salton Sea through the Temecula Valley and into the Los Angeles Basin, running roughly parallel to the San Andreas 80 km to the northeast. It comprises multiple segments — including the Whittier, Chino, and Glen Ivy strands — each capable of independent M6.5–7.5 ruptures that could affect suburban communities across Riverside and Orange counties. Although less continuously active than the San Jacinto Fault, paleoseismic data confirm repeated large-magnitude events throughout the Holocene.

Length

230 km

Max plausible

M7.5

Return period

~100–200 years per segment

The San Jacinto Fault Zone is the most seismically active fault system in Southern California, releasing more cumulative seismic moment per year than any other California fault including the San Andreas. It branches from the San Andreas near Cajon Pass and extends 230 km southeast through San Bernardino, Hemet, and the Salton Sea region, with a slip rate of 15–25 mm/year. The Anza and Clark segments are considered the most hazardous, with paleoseismic evidence for repeated M7.0–7.5 events and an estimated 25–30% probability of M6.7+ in the next 30 years.

Length

120 km

Max plausible

M7.0

Return period

~200–500 years for full-length rupture

The Calaveras Fault branches from the Hayward Fault near the Santa Cruz Mountains and runs northward through the East Bay to Hollister, where it merges back toward the San Andreas. It is one of the most active creeping faults in the Bay Area, with southern segments slipping aseismically at up to 15 mm/year, though the northern locked segment near Danville and Walnut Creek is capable of producing a M6.5–7.0 earthquake. The fault passes directly beneath the Calaveras Reservoir and crosses densely populated East Bay suburbs, making its northern locked section a significant hazard for Contra Costa and Alameda counties.

United States Geological Survey

National (USA)

Issues the ANSS (Advanced National Seismic System) catalog, ShakeMap intensity maps, and Did You Feel It community reports for all California earthquakes.

California Geological Survey

State (California)

Maps Alquist-Priolo earthquake fault zones and seismic hazard zones (liquefaction, landslide) used for land-use planning and building permits across California.

Southern California Earthquake Data Center

Southern California

Operated by Caltech, SCEDC archives the Southern California Seismic Network (SCSN) catalog — the most comprehensive seismicity record for Southern California dating to 1932.

ShakeAlert Earthquake Early Warning

West Coast (California, Oregon, Washington)

USGS-led early warning system in partnership with UC Berkeley and Caltech that delivers seconds-to-tens-of-seconds advance notice of shaking via the MyShake app, WEA, and Android Earthquake Alert.

USGS Prompt Assessment of Global Earthquakes for Response

Global (USGS)

Produces rapid fatality and economic loss estimates within 30 minutes of a significant earthquake to guide emergency response prioritization and resource deployment.