# Calaveras Fault

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Geological fault in northern California

For other uses of "Calaveras", see [Calaveras (disambiguation)](/source/Calaveras_(disambiguation)).

Calaveras Fault creep in downtown Hollister in April 2009

The **Calaveras Fault** is a major branch of the [San Andreas Fault](/source/San_Andreas_Fault) System that is located in northern [California](/source/California) in the [San Francisco Bay Area](/source/San_Francisco_Bay_Area). Activity on the different segments of the fault includes moderate and large earthquakes as well as [aseismic creep](/source/Aseismic_creep). The last large event was the magnitude 6.2 [1984 Morgan Hill event](/source/1984_Morgan_Hill_earthquake). The most recent moderate earthquakes were the magnitude 5.1 event on 25 October 2022, and the magnitude 5.6 [2007 Alum Rock event](/source/2007_Alum_Rock_earthquake).

It is believed to link with the Hayward fault, as well as the [West Napa Fault](/source/West_Napa_Fault), north of the Carquinez Strait. It passes through or near the cities of [Alamo](/source/Alamo%2C_California), [Danville](/source/Danville%2C_California), [San Ramon](/source/San_Ramon%2C_California), [Dublin](/source/Dublin%2C_California), [Pleasanton](/source/Pleasanton%2C_California), [Sunol](/source/Sunol%2C_California), [Milpitas](/source/Milpitas%2C_California), [San Jose](/source/San_Jose%2C_California), [Gilroy](/source/Gilroy%2C_California), and [Hollister](/source/Hollister%2C_California).

## Location

[Geological map](/source/Geological_map) of the Calaveras Fault

To the east of the Hayward-Rodgers Creek fault, the Calaveras fault extends 76 mi (123 km), splaying from the San Andreas fault near Hollister and terminating at Danville at its northern end.[1] (As of March 1978 it was believed that they did not quite connect.)[2] It runs east of the San Andreas, diverging from it in the vicinity of [Hollister, California](/source/Hollister%2C_California), and is responsible for the formation of the [Calaveras Valley](/source/Calaveras_Valley) there. Between the San Andreas Fault and the Calaveras Fault lies the [Hayward Fault](/source/Hayward_Fault_Zone), which diverges from the Calaveras Fault east of [San Jose, California](/source/San_Jose%2C_California). To the east lies the [Clayton-Marsh Creek-Greenville Fault](/source/Clayton-Marsh_Creek-Greenville_Fault). These four fault structures are some of the major [faults](/source/Fault_(geology)) in California at the [latitude](/source/Latitude) of [San Francisco](/source/San_Francisco). All are right lateral-moving strike-slip faults.

Elements of the San Andreas Fault System in the San Francisco Bay Area

The Calaveras Fault was named for [Calaveras Creek](/source/Calaveras_Creek_(California)) (in [Santa Clara County](/source/Santa_Clara_County%2C_California), east of San Jose), where it was first identified. ("Calaveras" is also the name of an unrelated [California county](/source/Calaveras_County%2C_California) in the western foothills of the [Sierra Nevada](/source/Sierra_Nevada) mountains, some 100 mi (160 km) east of Santa Clara County, far from the Calaveras Fault.) Some of the cities which the Calaveras Fault passes through or near are: [Alamo](/source/Alamo%2C_California), [Danville](/source/Danville%2C_California), [San Ramon](/source/San_Ramon%2C_California), [Dublin](/source/Dublin%2C_California), [Pleasanton](/source/Pleasanton%2C_California), [Sunol](/source/Sunol%2C_California), [Milpitas](/source/Milpitas%2C_California), [San Jose](/source/San_Jose%2C_California), [Gilroy](/source/Gilroy%2C_California), and [Hollister](/source/Hollister%2C_California).

## Related faults

The [West Napa Fault](/source/West_Napa_Fault) in [Napa County](/source/Napa_County%2C_California) is believed to be a continuation of the Calaveras Fault north of the [Carquinez Strait](/source/Carquinez_Strait). Between the faults lies an area of minor faults aligned [*en echelon*](/source/Echelon_formation#Geology) known as the Contra Costa Shear Zone.[3]

The minor [Concord Fault](/source/Concord_Fault) lies to the east of the Calaveras Fault, and small earthquakes occur in the gap between faults, mostly in the vicinity of [Alamo, California](/source/Alamo%2C_California), relieving stresses generated by the displacement between the two faults. Stresses are also produced by offset and converging slip-strike motions between the Calaveras and Clayton-Marsh Creek-Greenville Fault that continue to elevate [Mount Diablo](/source/Mount_Diablo). The compressive pressure is manifest in a significant [thrust fault](/source/Thrust_fault) nearby on the western slope of the mountain, the [Mount Diablo Thrust Fault](/source/Mount_Diablo_Thrust_Fault),[4] the most active of its kind in the region and which is also capable of producing significant local earthquakes affecting the Alamo-Danville area.

## Tectonic forces

The [Pacific plate](/source/Pacific_plate) is a major section of the Earth's crust, gradually expanding by the eruption of magma along the [East Pacific Rise](/source/East_Pacific_Rise) to the southeast. It is also being subducted far to the northwest into the [Aleutian Trench](/source/Aleutian_Trench) under the [North American plate](/source/North_American_plate) well north of San Francisco. In California, the plate is sliding northwestward along a transform boundary, the San Andreas Fault, toward the subduction zone. At the same time, the North American plate is moving southwestward, but relatively southeast along the fault. The westward component of the North American plate's motion results in some compressive force along the San Andreas and its associated faults such as the Calaveras Fault, thus helping lift the Coast Ranges. The Calaveras Fault shares the same relative motions of the San Andreas.

## Seismic activity

USGS ShakeMaps showing intensity patterns for the 1984 Morgan Hill (left) and 2007 Alum Rock events

Here are the notable recorded earthquakes on the Calaveras fault: 2022 (5.1), [2007 (5.6)](/source/2007_Alum_Rock_earthquake), [1984 (6.2)](/source/1984_Morgan_Hill_earthquake) and 1911 (6.5).

A number of magnitude 6 earthquakes have been recorded on the fault throughout recorded history, the largest of which was a magnitude 6.5 that occurred in 1911 in the [Morgan Hill](/source/Morgan_Hill%2C_California) area.[5] The most recent of these was a magnitude 6.2 earthquake near [Morgan Hill in 1984](/source/1984_Morgan_Hill_earthquake).

A [magnitude 5.6 earthquake](/source/2007_Alum_Rock_earthquake) occurred on the Calaveras Fault on October 30, 2007, at 20:04 [PDT](/source/Pacific_Time_Zone#Daylight_saving_time) (October 31, at 03:04 [UTC](/source/Coordinated_Universal_Time)), near [Alum Rock](/source/Alum_Rock%2C_San_Jose). Prior to the [2014 South Napa earthquake](/source/2014_South_Napa_earthquake), it was the most powerful quake to hit the Bay Area since the [1989 Loma Prieta earthquake](/source/1989_Loma_Prieta_earthquake), and the largest on the Calaveras Fault since 1984. On October 25, 2022, at 11:42 PDT (October 25, at 18:42 UTC), a magnitude 5.1 earthquake occurred on the fault near [Lick Observatory](/source/Lick_Observatory).[6]

## Hayward Fault connection

Although it has been known for some time that the Calaveras and Hayward faults merge in the South Bay region, recent geological studies[7] suggest that the Calaveras and Hayward faults may be even more closely connected horizontally deep beneath the surface, angling toward each other with depth until they become a single fault. If true, this would have significant implications for the potential maximum strength of earthquakes on the Hayward, since this strength is determined by the maximum length of the fault rupture and this rupture could extend beyond the juncture point to include some portion of the Calaveras.

## Recent assessment

Assessments in January 2008 suggest that the northern Calaveras fault (the portion between [Sunol](/source/Sunol%2C_California) and [Danville](/source/Danville%2C_California)) may be more likely to fail in the next few decades than previously thought.[8]

## See also

- [Bernal Subbasin](/source/Bernal_Subbasin)

- [Tesla Fault](/source/Tesla_Fault)

## References

1. **[^](#cite_ref-1)** Working Group on California Earthquake Probabilities, ["Characterization of the SFBR Earthquake Sources"](https://pubs.usgs.gov/of/2003/of03-214/OFR-03-214_FullText.pdf) (PDF), *Earthquake Probabilities in the San Francisco Bay Region: 2002–2031*, Open-File Report 03-214, United States Geological Survey, p. 16

1. **[^](#cite_ref-2)** ["A STUDY OF FAULT PLANE MECHANISMS PRECEDING THE THANKSGIVING DAY, 1974 EARTHQUAKE AT HOLLISTER, CALIFORNIA"](https://pubs.usgs.gov/of/1978/0255/report.pdf) (PDF). *pubs.usgs.gov*. March 1978. Retrieved 11 Oct 2025.

1. **[^](#cite_ref-3)** [http://gsa.confex.com/gsa/2005CD/finalprogram/abstract_85559.htm](http://gsa.confex.com/gsa/2005CD/finalprogram/abstract_85559.htm) *gsa.confex.com*

1. **[^](#cite_ref-4)** [https://www.pbs.org/newshour/indepth_coverage/science/1906quake/map6.html](https://www.pbs.org/newshour/indepth_coverage/science/1906quake/map6.html) [Archived](https://web.archive.org/web/20121102221326/http://www.pbs.org/newshour/indepth_coverage/science/1906quake/map6.html) 2012-11-02 at the [Wayback Machine](/source/Wayback_Machine) PBS

1. **[^](#cite_ref-5)** ["Historic Earthquakes: Calaveras fault, California"](https://web.archive.org/web/20091110071300/http://earthquake.usgs.gov/earthquakes/states/events/1911_07_01.php). Archived from [the original](https://earthquake.usgs.gov/earthquakes/states/events/1911_07_01.php) on 2009-11-10. Retrieved 25 November 2008.

1. **[^](#cite_ref-6)** ["M 5.1 – 15 km ESE of Alum Rock, CA"](https://web.archive.org/web/20221025184758/https://earthquake.usgs.gov/earthquakes/eventpage/nc73799091/executive). United States Geological Survey. Archived from [the original](https://earthquake.usgs.gov/earthquakes/eventpage/nc73799091/executive) on 2022-10-25. Retrieved 26 October 2022.

1. **[^](#cite_ref-7)** Perlman, David (December 12, 2007). ["Hayward, Calaveras faults may be connected, geologist says"](https://www.sfgate.com/bayarea/article/Hayward-Calaveras-faults-may-be-connected-3234475.php). *San Francisco Chronicle*.

1. **[^](#cite_ref-8)** [*Hayward fault might be more dangerous than scientists thought*](http://www.mercurynews.com/news/ci_8028422) (*San Jose Mercury News*)

## Further reading

- Chaussard, E.; Bürgmann, R.; Fattahi, H.; Johnson, C. W.; Nadeau, R.; Taira, T.; Johanson, I. (2015). ["Interseismic coupling and refined earthquake potential on the Hayward-Calaveras fault zone"](https://authors.library.caltech.edu/records/64pcy-n1945/files/Chaussard_et_al-2015-Journal_of_Geophysical_Research__Solid_Earth.pdf?download=1) (PDF). *Journal of Geophysical Research: Solid Earth*. **120** (12): 8570–8590. [Bibcode](/source/Bibcode_(identifier)):[2015JGRB..120.8570C](https://ui.adsabs.harvard.edu/abs/2015JGRB..120.8570C). [doi](/source/Doi_(identifier)):[10.1002/2015jb012230](https://doi.org/10.1002%2F2015jb012230). [ISSN](/source/ISSN_(identifier)) [2169-9313](https://search.worldcat.org/issn/2169-9313).

- Harris, R. A.; Barall, M.; Lockner, D. A.; Moore, D. E.; Ponce, D. A.; Graymer, R. W.; Funning, G.; Morrow, C. A.; Kyriakopoulos, C.; Eberhart-Phillips, D. (2021). ["A Geology and Geodesy Based Model of Dynamic Earthquake Rupture on the Rodgers Creek-Hayward-Calaveras Fault System, California"](https://escholarship.org/content/qt953625x2/qt953625x2.pdf?t=qoh57h) (PDF). *Journal of Geophysical Research: Solid Earth*. **126** (3) e2020JB020577. [Bibcode](/source/Bibcode_(identifier)):[2021JGRB..12620577H](https://ui.adsabs.harvard.edu/abs/2021JGRB..12620577H). [doi](/source/Doi_(identifier)):[10.1029/2020jb020577](https://doi.org/10.1029%2F2020jb020577). [ISSN](/source/ISSN_(identifier)) [2169-9313](https://search.worldcat.org/issn/2169-9313).

- McClellan, P. H.; Hay, E. A. (1990). "Triggered slip on the Calaveras Fault during the magnitude 7.1 Loma Prieta, California, Earthquake". *Geophysical Research Letters*. **17** (8): 1227–1230. [Bibcode](/source/Bibcode_(identifier)):[1990GeoRL..17.1227M](https://ui.adsabs.harvard.edu/abs/1990GeoRL..17.1227M). [doi](/source/Doi_(identifier)):[10.1029/gl017i008p01227](https://doi.org/10.1029%2Fgl017i008p01227). [ISSN](/source/ISSN_(identifier)) [0094-8276](https://search.worldcat.org/issn/0094-8276).

## External links

- [M6.9 Earthquake on the Calaveras Fault](https://www.youtube.com/watch?v=-mY9c-xC2fM) – [Southern California Earthquake Center](/source/Southern_California_Earthquake_Center)

- [ABAG shaking hazard maps](https://web.archive.org/web/20141011070221/http://resilience.abag.ca.gov/earthquakes/)

- [Tracking the Elusive Calavaras Fault from Sunol to San Ramon](https://web.mst.edu/~rogersda/forensic_geology/calaveras_fault/calaveras_fault.htm)

v t e Seismically active fault zones and tectonic blocks of California Statewide Faults San Andreas Fault Salinian Block Southern California Brawley Seismic Zone Chino Fault Elsinore Fault Zone Elysian Park Fault Garlock Fault Hollywood fault Hosgri Fault Imperial Fault Zone Laguna Salada Fault Newport–Inglewood Fault Northridge Blind Thrust Fault Peninsular Ranges Puente Hills Fault Raymond Fault Rose Canyon Fault Salton Trough San Cayetano Fault San Diego Trough Fault Zone San Felipe Fault Zone San Gabriel Fault San Jacinto Fault Zone Santa Maria River Fault Santa Ynez Fault Shoreline Fault Sierra Madre Fault Zone Ventura Fault White Wolf Fault Whittier Fault Yorba Linda Fault Northern California Bartlett Springs Fault Calaveras Fault Clayton-Marsh Creek-Greenville Fault Concord Fault Hayward Fault Zone Healdsburg Fault Maacama Fault Mendocino fracture zone Mendocino triple junction Mount Diablo Thrust Fault Monta Vista Fault Nacimiento Fault Pleasanton Fault Rinconada Fault San Gregorio Fault San Pablo Fault Seal Cove Fault Serra Fault Silver Creek Fault Tesla Fault West Napa Fault Sierra Nevada Death Valley Fault Zone Furnace Creek Fault Zone Honey Lake Fault Zone Kern Canyon Fault Maria fold and thrust belt Owens Valley Fault Rescue Lineament-Bear Mountains fault zone Sierra Nevada Batholith Sierra Nevada Fault Sierra Nevada–Great Valley Block Smartville Block Walker Lane Category California Geological Survey Seismic Hazards Mapping Act Mexico (list)

v t e Major seismically active faults of North America North America (crosses national borders) Aleutian Trench (US–RU) Basin and Range Province (US–MX) Canadian Arctic Rift System (CA–GL) Cascadia subduction zone (US–CA) Clarendon-Linden fault system (US–CA) Denali Fault (US–CA) Northern Cordilleran Volcanic Province (CA–US) Puget Sound faults (US–CA) Rio Grande rift (US–MX) San Andreas Fault (US–MX) Southern Great Lakes seismic zone (US–CA) Tintina Fault (US–CA) Canada Charlevoix seismic zone Laurentian Slope seismic zone Leech River Fault Queen Charlotte Fault Saguenay Graben Saint Lawrence rift system Timiskaming Graben Western Quebec seismic zone United States Washington and Oregon Brothers Fault Zone Olympic–Wallowa lineament Puget Sound (Seattle Fault, Tacoma Fault) Walker Lane California Calaveras Fault Garlock Fault Hayward Fault Zone Mendocino fracture zone Newport–Inglewood Fault Puente Hills Fault Rose Canyon Fault San Jacinto Fault Zone (Elsinore Fault Zone) Great Basin Independence Valley fault system Moab Fault Teton Fault Wasatch Fault Great Plains Humboldt Fault Long Point–Eureka Heights fault system Meers Fault Nemaha Fault Zone Midwest Marianna Fault New Madrid seismic zone Sandwich Fault Zone Wabash Valley seismic zone Appalachian Mountains and Atlantic Coast Charleston seismic zone Eastern Tennessee seismic zone Northern Appalachians seismic zone Ramapo Fault Virginia seismic zones Alaska Salcha seismic zone Caribbean and Mexico Cayman Trough Chixoy-Polochic Fault Enriquillo–Plantain Garden fault zone (Cuba) Gulf of California Rift Zone Lesser Antilles subduction zone Middle America Trench (Central America) Motagua Fault (Central America) Pedro Miguel Fault Puerto Rico Trench

v t e San Francisco Bay Area Bodies of water Bodega Bay Carquinez Strait Clifton Forebay Golden Gate Grizzly Bay Guadalupe River Half Moon Bay Lake Berryessa Napa River Oakland Estuary Petaluma River Richardson Bay Richmond Inner Harbor Russian River Sacramento River San Francisco Bay San Leandro Bay San Pablo Bay Sonoma Creek Suisun Bay Tomales Bay Counties Alameda Contra Costa Marin Napa San Francisco San Mateo Santa Clara Solano Sonoma Cities and towns Major cities Oakland San Francisco San Jose 100k–250k Antioch Berkeley Concord Daly City Fairfield Fremont Hayward Richmond San Mateo Santa Clara Santa Rosa Sunnyvale Vacaville Vallejo 50k–100k Alameda Brentwood Cupertino Dublin Gilroy Livermore Milpitas Mountain View Napa Novato Palo Alto Petaluma Pittsburg Pleasanton Redwood City San Leandro San Rafael San Ramon South San Francisco Union City Walnut Creek 25k–50k Belmont Benicia Burlingame Campbell Danville East Palo Alto El Cerrito Foster City Hercules Lafayette Los Altos Los Gatos Martinez Menlo Park Morgan Hill Newark Oakley Pacifica Pleasant Hill Rohnert Park San Bruno San Carlos San Pablo Saratoga Suisun City Windsor 10k–25k Albany American Canyon Clayton Corte Madera Dixon Emeryville Half Moon Bay Healdsburg Hillsborough Larkspur Mill Valley Millbrae Moraga Orinda Piedmont Pinole Rio Vista San Anselmo Sonoma Under 10k Atherton Belvedere Brisbane Calistoga Cloverdale Colma Cotati Fairfax Los Altos Hills Monte Sereno Portola Valley Ross St. Helena Sausalito Sebastopol Tiburon Woodside Yountville CDPs over 10k Alamo Alum Rock Ashland Bay Point Castro Valley Cherryland Discovery Bay El Sobrante Fairview North Fair Oaks San Lorenzo Stanford Tamalpais-Homestead Valley Sub-regions East Bay North Bay Peninsula San Francisco South Bay Other Homelessness Politics Sports Transportation

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Adapted from the Wikipedia article [Calaveras Fault](https://en.wikipedia.org/wiki/Calaveras_Fault) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Calaveras_Fault?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.