The Concord Fault is a

geologic fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

in the

San Francisco Bay Area The San Francisco Bay Area, commonly known as the Bay Area, is a List of regions of California, region of California surrounding and including San Francisco Bay, and anchored by the cities of Oakland, San Francisco, and San Jose, California, S ...

. The reason it is called that is because it is located under the city of Concord. It is connected to, and considered to be part of, the same fault zone as the Green Valley fault, which lies just a few miles to the north across the

Suisun Bay Suisun Bay ( ; Wintun for "where the west wind blows") is a shallow tidal estuary (a northeastern extension of the San Francisco Bay) in Northern California. It lies at the confluence of the Sacramento River and San Joaquin River, forming the e ...

. The fault is situated at the east of West Napa Fault and extends from

Mount Diablo Mount Diablo is a mountain of the Diablo Range, in Contra Costa County, California, Contra Costa County of the eastern San Francisco Bay Area in Northern California. It is south of Clayton, California, Clayton and northeast of Danville, Califo ...

to the

Carquinez Strait The Carquinez Strait (; Spanish: ''Estrecho de Carquinez'') is a narrow tidal strait located in the Bay Area of Northern California, United States. It is part of the tidal estuary of the Sacramento and the San Joaquin rivers as they drain int ...

, an approximately 11 mile long distance. Like most other faults in this area, the Concord Fault is a

strike-slip In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

fault, moving approximately 2.7 to 3.6 millimeters a year.

Seismic activity

Currently, it is considered to be under a high stress level and therefore has a higher chance of a major earthquake happening. There have been

earthquakes 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 c ...

on this fault before. On October 23, 1955, a 5.4

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 ...

quake caused about 1 million dollars in damage (about 8.7 million today) and one death. The last large earthquake linked to this fault occurred over 400 years ago.

Dangers

According to

USGS The United States Geological Survey (USGS), founded as the Geological Survey, is an government agency, agency of the United States Department of the Interior, U.S. Department of the Interior whose work spans the disciplines of biology, geograp ...

seismologists it is "the most urban fault" in the

East Bay The East Bay is the eastern region of the San Francisco Bay Area and includes cities along the eastern shores of San Francisco Bay and San Pablo Bay. The region has grown to include inland communities in Alameda and Contra Costa counties. Wi ...

, with potential for a larger event than the

2014 South Napa earthquake The 2014 South Napa earthquake occurred in the North Bay (San Francisco Bay Area), northern San Francisco Bay Area on August 24 at . At 6.0 on the moment magnitude scale and with a maximum Mercalli intensity scale, Mercalli intensity of VIII (''S ...

. As critical infrastructure, including refineries that process a significant portion of the state's total

crude oil Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring u ...

, and a railroad bridge, lie under it, a major earthquake from it could leave the entire northern half of the state without fuel and disrupt transmission of electricity and water to some extent across the state. One particular pumping station, if hit by a quake, would particularly damage transmission of fuel. A major earthquake there could also cause flooding, which would impact drinking quality, and a loss of electricity.

References

Seismic faults of California Geology of Contra Costa County, California Concord, California Mount Diablo Geography of the San Francisco Bay Area {{tectonics-stub