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 aseismic creep . The last large event was the magnitude 6.2 1984 Morgan Hill event . The most recent moderate earthquakes were the magnitude 5.1 event on 25 October 2022, and the magnitude 5.6 2007 Alum Rock event .
18-825: It is believed to link with the Hayward fault, as well as the West Napa Fault , north of the Carquinez Strait. It passes through or near the cities of Alamo , Danville , San Ramon , Dublin , Pleasanton , Sunol , Milpitas , San Jose , Gilroy , and Hollister . To the east of the Hayward-Rodgers Creek fault, the Calaveras fault extends 123 km (76 mi), splaying from the San Andreas fault near Hollister and terminating at Danville at its northern end. It runs east of
36-639: Is manifest in a significant thrust fault nearby on the western slope of the mountain, the Mount Diablo Thrust Fault , the most active of its kind in the region and which is also capable of producing significant local earthquakes affecting the Alamo-Danville area. The Pacific plate is a major section of the Earth's crust, gradually expanding by the eruption of magma along the East Pacific Rise to
54-585: The 2000 Yountville earthquake which occurred on September 3, 2000, is also near the West Napa Fault. 2007 Alum Rock earthquake The 2007 Alum Rock earthquake occurred on October 30 at 8:04 p.m. Pacific Daylight Time in Alum Rock Park in San Jose , in the U.S. state of California . It measured 5.6 on the moment magnitude scale and had a maximum Mercalli intensity of VI ( Strong ). The event
72-541: The Calaveras Fault and ruptured an area of the fault for a length of about 5 km (3.1 mi) beginning at the hypocenter and extending southeast. There was no evidence of any surface rupture along the fault caused by the earthquake . David Oppenheimer, a seismologist at the United States Geological Survey (USGS), said that although the quake was felt as a strong jolt over a wide region, it
90-531: The San Francisco Bay Area in northern California . It is believed to be the northern extension of the Calaveras Fault in the East Bay region. It has been mapped as a Late Pleistocene - Holocene active fault , 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 . In 2023 there
108-591: The Calaveras Fault. Some of the cities which the Calaveras Fault passes through or near are: Alamo , Danville , San Ramon , Dublin , Pleasanton , Sunol , Milpitas , San Jose , Gilroy , and Hollister . The West Napa Fault in Napa County is believed to be a continuation of the Calaveras Fault north of the Carquinez Strait . Between the faults lies an area of minor faults aligned en echelon known as
126-408: 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
144-539: The Contra Costa Shear Zone. The minor 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 , 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 . The compressive pressure
162-548: 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. Here are the notable recorded earthquakes on the Calaveras fault: 2022 (5.1), 2007 (5.6) , 1984 (6.2) and 1911 (6.5). A number of magnitude 6 earthquakes have been recorded on
180-652: The San Andreas, diverging from it in the vicinity of Hollister, California , and is responsible for the formation of the Calaveras Valley there. Between the San Andreas Fault and the Calaveras Fault lies the Hayward Fault , which diverges from the Calaveras Fault east of San Jose, California . To the east lies the Clayton-Marsh Creek-Greenville Fault . These four fault structures are some of
198-458: The fault throughout recorded history, the largest of which was a magnitude 6.5 that occurred in 1911 in the Morgan Hill area. The most recent of these was a magnitude 6.2 earthquake near Morgan Hill in 1984 . A magnitude 5.6 earthquake occurred on the Calaveras Fault on October 30, 2007, at 20:04 PDT (October 31, at 03:04 UTC ), near Alum Rock . Prior to the 2014 South Napa earthquake , it
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#1732851087603216-502: The juncture point to include some portion of the Calaveras. Assessments in January 2008 suggest that the northern Calaveras fault (the portion between Sunol and Danville ) may be more likely to fail in the next few decades than previously thought. West Napa Fault The West Napa Fault is a 57 km (35 mi) long geologic fault in Napa County , in the North Bay region of
234-624: The major faults in California at the latitude of San Francisco . All are right lateral-moving strike-slip faults. The Calaveras Fault was named for Calaveras Creek in Santa Clara County east of San Jose where it was first identified. ( Calaveras is Spanish for "skulls".) "Calaveras" is also the name of a California county in the foothills of the Sierra Nevada mountains, some 100 miles (160 km) east of Santa Clara County, far from
252-529: The southeast. It is also being subducted far to the northwest into the Aleutian Trench under the 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
270-405: Was data showing that the West Napa Fault is actually nine miles longer than previously known. 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
288-452: Was more significant because it caused stress changes in the Calaveras Fault and the nearby Hayward Fault . Intensity VI ( Strong ) effects included broken windows and items that were knocked off store shelves, but the event caused no serious damage or injuries. Some parts of the Bay Area felt the rupture for up to 15 seconds. ElarmS, an earthquake early warning system, accurately predicted
306-589: Was the most powerful quake to hit the Bay Area since the Loma Prieta earthquake of 1989, 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 . Although it has been known for some time that the Calaveras and Hayward faults merge in the South Bay region, recent geological studies suggest that
324-485: Was then the largest in the San Francisco Bay Area since the 1989 Loma Prieta earthquake , which measured 6.9 on the moment magnitude scale, but was later surpassed by the 2014 South Napa earthquake . Ground shaking from the Alum Rock quake reached San Francisco and Oakland and other points further north. Sixty thousand felt reports existed far beyond Santa Rosa, as far north as Eugene, Oregon . The shock originated on
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