The San Gregorio Fault is an active, 209 km (130 mi) long fault located off the coast of

Northern California Northern California (commonly shortened to NorCal) is a geocultural region that comprises the northern portion of the U.S. state of California, spanning the northernmost 48 of the state's List of counties in California, 58 counties. Northern Ca ...

. The southern end of the fault is in the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

just south of

Monterey Bay Monterey Bay is a bay of the Pacific Ocean located on the coast of the U.S. state of California, south of the San Francisco Bay Area. San Francisco itself is further north along the coast, by about 75 miles (120 km), accessible via California S ...

, and the northern end is about 20 km northwest of

San Francisco San Francisco, officially the City and County of San Francisco, is a commercial, Financial District, San Francisco, financial, and Culture of San Francisco, cultural center of Northern California. With a population of 827,526 residents as of ...

, near Bolinas Bay, where the San Gregorio intersects the

San Andreas Fault The San Andreas Fault is a continental Fault (geology)#Strike-slip faults, right-lateral strike-slip transform fault that extends roughly through the U.S. state of California. It forms part of the tectonics, tectonic boundary between the Paci ...

. Most of the San Gregorio

fault trace A fault trace describes the intersection of a Fault (geology), geological fault with the Earth's surface, which leaves a visible disturbance on the surface, usually looking like a crack in the surface with jagged rock structures protruding outwar ...

is located offshore beneath the waters of Monterey Bay,

Half Moon Bay Half Moon Bay is a coastal city in San Mateo County, California, San Mateo County, California, United States, approximately south of San Francisco. Its population was 11,795 2020 United States census, 2020 census. Immediately north of Half Mo ...

, and the Pacific Ocean, though it cuts across land near Point Año Nuevo and Pillar Point. The San Gregorio Fault is part of a system of coastal faults which run roughly parallel to the San Andreas. The movement of the San Gregorio is right-lateral strike-slip, and the slip rate is estimated to be 4–10 mm/year (0.2–0.4 inch/year). The most recent major

earthquake An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

along the fault had an estimated

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

of 7 to 7.25 and occurred after 1270 AD—the earliest calibrated radiocarbon date for a native Californian cooking hearth at the Seal Cove site near Moss Beach that shows signs of displacement—but before 1775, when Spanish missionaries arrived in northern California and recorded history began for the region. Portions of the fault that come ashore near the cliffs between Pillar Point and Moss Beach are sometimes referred to as "Seal Cove Fault" in the geological literature.

References

{{California Faults Seismic faults of California Geology of Marin County, California Geology of Monterey County, California Geology of San Francisco Geology of San Mateo County, California Geology of Santa Cruz County, California Geography of the San Francisco Bay Area Monterey Bay