Overview
- The fault is a right‑lateral transform boundary separating the Pacific and North American plates, according to the USGS.
- It extends roughly 1,200 km, reaches depths of up to about 15 km, and slips at 20–35 mm per year within a broad, branching fault zone.
- The system runs from near the Salton Sea northwest to Cape Mendocino, passing close to Los Angeles, San Bernardino, and San Francisco and linking to Baja California in Mexico.
- Large historical earthquakes near magnitude 7.8 struck in 1857 and 1906, and experts note the southern segment has not ruptured since 1857, indicating ongoing strain accumulation.
- With no reliable way to predict exact timing, UCERF3 estimates about a 7% chance of M≥8 in California over 30 years and roughly 31% for an M7.5 in the south, while the USGS ShakeOut scenario projects thousands of casualties and extensive damage for a modeled M7.8 event.