The West Napa Fault is a long

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 ...

Napa County Napa County () is a county north of San Pablo Bay located in the northern portion of the U.S. state of California. As of the 2020 census, the population was 138,019. The county seat is the City of Napa. Napa County was one of the original co ...

, in the North Bay region of the

San Francisco Bay Area The San Francisco Bay Area, often referred to as simply the Bay Area, is a populous region surrounding the San Francisco, San Pablo, and Suisun Bay estuaries in Northern California. The Bay Area is defined by the Association of Bay Area Go ...

in northern

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

. It is believed to be the northern extension of the

Calaveras Fault The Calaveras Fault is a major branch of the San Andreas Fault System that is located in northern California in the San Francisco Bay Area. Activity on the different segments of the fault includes moderate and large earthquakes as well as aseismi ...

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 the San Francisco Bay and San Pablo Bay. The region has grown to include inland communities in Alameda and Contra Costa countie ...

region. It has been mapped as a

Late Pleistocene The Late Pleistocene is an unofficial Age (geology), age in the international geologic timescale in chronostratigraphy, also known as Upper Pleistocene from a Stratigraphy, stratigraphic perspective. It is intended to be the fourth division of ...

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

active fault An active fault is a fault that is likely to become the source of another earthquake sometime in the future. Geologists commonly consider faults to be active if there has been movement observed or evidence of seismic activity during the last 10,0 ...

, and is considered to be predominantly a right lateral strike-slip fault. The fault was discovered in 1976 by Gene Boudreau, a ground water drilling specialist from

Sebastopol Sevastopol (; uk, Севасто́поль, Sevastópolʹ, ; gkm, Σεβαστούπολις, Sevastoúpolis, ; crh, Акъя́р, Aqyár, ), sometimes written Sebastopol, is the largest city in Crimea, and a major port on the Black Sea ...

Earthquakes

The West Napa Fault is a likely source for the magnitude 6.0 South Napa earthquake that hit Napa County on August 24, 2014. Seismologists were not able to determine the exact fault on which the quake occurred, because faults are usually identified by their expression on the surface. The epicenter for the 2000 Yountville earthquake which occurred on September 3, 2000 is also near the West Napa Fault.

References

{{Quaternary Footer Seismic faults of California Geology of Napa County, California Napa, California Strike-slip faults Late Pleistocene Pleistocene California Quaternary California Holocene North America

Earthquakes

See also

References