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

Northern California Northern California (colloquially known as NorCal) is a geographic and cultural region that generally comprises the northern portion of the U.S. state of California. Spanning the state's northernmost 48 counties, its main population centers incl ...

. The southern end of the fault is in southern

Monterey Bay Monterey Bay is a bay of the Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica ...

, and the northern end is about 20 km northwest of

San Francisco San Francisco (; Spanish language, Spanish for "Francis of Assisi, Saint Francis"), officially the City and County of San Francisco, is the commercial, financial, and cultural center of Northern California. The city proper is the List of Ca ...

, near

Bolinas Bay Bolinas Bay is a small bay, approximately 5 miles (8 km) long, on the Pacific coast of California in the United States. It is in Marin County, north of the Golden Gate, approximately 15 miles (25 km) northwest of San Francisco. The tow ...

, where the San Gregorio intersects the

San Andreas Fault The San Andreas Fault is a continental transform fault that extends roughly through California. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal) ...

. Most of the San Gregorio

fault trace A fault trace describes the intersection of a 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 outward. The term als ...

is located offshore beneath the waters of Monterey Bay,

Half Moon Bay Half Moon Bay is a coastal city in San Mateo County, California, United States, approximately south of San Francisco. Its population was 11,795 as of the 2020 census. Immediately at the north of Half Moon Bay is Pillar Point Harbor and the un ...

, and the

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

, though it cuts across land near Point Año Nuevo and

Pillar Point Pillar Point may refer to: * Pillar Point (band) *Pillar Point Air Force Station *Pillar Point Harbor Pillar Point Harbor is a boat harbor created by a riprap breakwater in San Mateo County, California immediately north of Half Moon Bay. It is ...

. 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 earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

along the fault had an estimated magnitude 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.

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