Within a minute, it was followed by a 3.6-magnitude quake along the Calaveras Fault in Santa Clara County. Another swarm struck the central portion of the Calaveras Fault in April 2016 (http://temblor.net/earthquake-insights/calaveras-535/); neither triggered a larger shock. With a slip rate of about 15 mm/yr (0.6 in/yr) and a length of about 100 km (60 mi), the Calaveras is highly active and certainly capable of a M7+ earthquake. That makes it a favorite laboratory for Earth Scientists and students to see faulting in slow-motion. “After the landslides were removed, we found additional, smaller faults that had not been recognized during the original design studies for the new dam” said Rick Harlan, an engineering geologist who worked for the SFPUC’s construction management team during the dam replacement project. Kelson, K. I., Simpson, G. D., Lettis, W. R., & Haraden, C. C. (1996). “We really don’t know what causes an earthquake swarm,” said Roland Burgmann, a geologist at the University of California-Berkeley. During the past week, 75 quakes have rattled the beautiful town of Danville, scene of the beloved Robin Williams movie, “Mrs. future moderate earthquakes on the Calaveras Fault. Risk … The initial earthquake The HCFZ considered here encompasses the HF, the northern CF, and the central CF from the junction with the northern CF to Gilroy (Figure 1). The Calaveras Fault, like the San Andreas Fault to the west, is a right-lateral strike-slip fault that is part of the San Andreas Fault System in the San Francisco Bay region. Digital compilation of Northern Calaveras Fault data for the Northern California map database: collaborative research with William Lettis & Associates, Inc., and the US Geological Survey. The Calaveras Fault: It is possible to walk down Locust Street from Vista Hill Park and walk through the neighborhood to examine the structural damage to streets, curbs, walls, and buildings that are slowly being deformed, warped, or broken by the slow creeping motion of the Calaveras Fault. The north-northwest trending Calaveras Fault makes a westward bend or stepover under the northern end of the reservoir, crossing from the east bank of the reservoir south of the dam to the west side of Observation Hill which forms the left (west) abutment of the dam, according to a technical report on the Calaveras Fault. The quake was reported at 10:35 a.m. and was centered east of Alum Rock Park. The Calaveras fault produced the M6.2 Morgan Hill Earthquake in 1984. Holocene slip rate and earthquake recurrence of the northern Calaveras fault at Leyden Creek, northern California. This is a relief to the 27 million residents who rely on the Calaveras Reservoir. By Melissa L. Weber, science writer (@Melwriter), Citation: Weber, M., 2020, Earthquake swarm rattles ground near new Calaveras Dam, Temblor, http://doi.org/10.32858/temblor.124, Aerial view of the Calaveras Reservoir, looking to the east. Only one 1911 seismogram from the U.S. survived, from the University of St. Louis, which was saved by Prof. John Ebel, former director of the Weston Observatory of Boston College. The white lines … The reservoir sits atop a major branch of the San Andreas Fault system called the Calaveras Fault. “I think the swarm is just a good reminder of seismic hazard that exists along the fault.”. The largest earthquake within 30 miles of Calaveras County, CA was a 3.3 Magnitude in 2017.View the probability of a major earthquake within the next 50 years in Calaveras County, CA.View the number of earthquake incidents in Calaveras County, CA by year that are more than 2.5 Magnitude. The Calaveras fault system runs over 80 miles, from south of Hollister into the Danville-Walnut Creek area. Within a minute, it was followed by a magnitude 3.6 quake along the Calaveras Fault in Santa Clara County. The northern segment of the Calaveras Fault is virtually locked and this segment of the fault creeps at a rate between 2 and 3 mm/yr. Historical storage records suggest the recent re-filling of Calaveras reservoir is also not a likely culprit, since similar reservoir fluctuations have occurred in the past without triggering pulses of seismicity in that area. California Geological Survey We use specialized high … The Calaveras Fault and lost seismograms . The north-northwest trending Calaveras Fault makes a westward bend or stepover under the northern end of the reservoir, crossing from the east bank of the reservoir south of the dam to the west side of Observation Hill which forms the left (west) abutment of the dam, according to a technical report on the Calaveras Fault. It's a kind of "Faults For Dummies!" The fault cuts through the towns of Walnut Creek, San Ramon, Dublin, Pleasanton, Sunol, and Hollister. The Calaveras Fault is a mostly right-lateral, strike-slip fault. Construction on a new earth-and-rock-fill dam began in 2011 and was completed in May 2019, according to the SFPUC. Construction on the new Calaveras Dam exposed faults not previously mapped. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal). The first was a 4.0 magnitude earthquake about six miles northeast of San Martin around 6:48 a.m., according to USGS, and another shortly after east of Morgan Hill. In Hollister the Calaveras Fault is displaying aseismic motion—one side of the fault is slipping past the other side of … The largest historical quake on the Calaveras Fault was a M6.6 earthquake in 1911. The earthquake faults in California, including the Hayward, the Calaveras and the San Andreas faults. A magnitude 3.7 earthquake was reported Tuesday morning 2 miles from Morgan Hill, according to the U.S. Geological Survey. In other words, we don’t know for certain if this northern section of the Calaveras Fault is due for another big quake in the near future. Over 70 quakes have struck in the area around the Calaveras Dam since mid-August. Map of active fault traces, geomorphic features and Quaternary surficial deposits along the Central Calaveras fault, Santa Clara County, California. Credit: Rick Harlan (used with permission of SFPUC). At the southern end of its central stretch it creeps at about 14 mm/yr dropping northward to about 6 mm/yr (0.24 inch/yr) of creep at its … The San Andreas Fault is a continental transform fault that extends roughly 1,200 kilometers (750 mi) through California. Swarms likely light up portions of faults that suddenly begin to creep—or slip at a much higher rate than usual. Because of this, “the static stress change at depth must have been minimal.” This suggests that excavation during dam construction is not likely to be the cause of this swarm. The largest earthquake within 30 miles of Calaveras County, CA was a 3.3 Magnitude in 2017. The Hayward Fault splinters from the Calaveras Fault, which itself is an offshoot of the The white lines indicate faults recognized by the USGS. “As I understand it, the excavated material [at Calaveras] was mostly put back into the nearby new dam embankment,” he said. Along some active faults, deformation and offset occur continuously even in the absence of large earthquakes; this is referred to as fault creep which generally proceeds at rates of millimeters to tens of millimeters per year. USSD Dams and Levees Bulletin of the United States Society on Dams Summer 2019 Issue No. This earthquake and its aftershocks took place within a very dense seismic network. Doubtfire.” The quakes are occurring at a depth of 5-7 km (3-4 mi) on a heretofore unmapped fault or set of faults, and exhibit a diversity of mechanisms, some similar to the ‘right-lateral’ (whichever side you are on, the other side moves to the right) Calaveras Fault, and others perhaps related to the ‘blind thrust fault’ that has jacked up Mount Diablo. In California, the plate is sliding northwestward along a transform boundary, the San Andreas Fault, toward the subduction zone. On 6 August 1979, a magnitude 5.7 earthquake occurred along the Calaveras fault zone in the Coyote Lake area of central California. Along sections of the Central San Andreas and southern Calaveras faults in California, we map rates and patterns of fault creep over 150 km by comparing two older airborne … 178, pg. The SFPUC began refilling the Calaveras Reservoir last year, after dam construction was completed, and as of now it is at 62% capacity, according to the SFPUC. The USGS database shows that there is a 19.41% chance of a major earthquake within 50km of Calaveras County, CA within the next 50 years. The largest historical quake on the Calaveras Fault was a M=6.6 event in 1911 (Doser, 2009), but far too … UC Berkeley seismologists have proven that the Hayward Fault is essentially a branch of the Calaveras Fault that runs east of San Jose, which means that both could rupture together, resulting in a significantly more destructive earthquake than previously thought. As a precaution, the water levels in the reservoir were lowered to about 40% capacity in an attempt to mitigate downstream hazard should a major earthquake compromise the dam. The Bay Area fault system and the spot (red star) where the Hayward Fault branches off from the Calaveras Fault. The 2 to 8mm/yr range of creep rates along the HF is well documented by over 30 alignment arrays (AAs) and 5 creepmeters covering … A magnitude-1.9 tremor on October 8 was the latest in a series of small earthquakes near Northern California’s Calaveras Dam, located about 38 miles (61 kilometers) southeast of San Francisco. The SFPUC’s Completion Fact Sheet for the recently completed Calaveras Dam Replacement Project (CDRP) indicates that the fault runs only about 1,000 feet (300 meters) from the new dam (SFPUC, 2019). While … 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 the southeast. Hayward-Calaveras fault zone (HCFZ), characterization of the creep rates along the faults with a high spatial resolution is necessary. Credit: Dicklyon (CC BY-SA 4.0). Some 600 quakes struck San Ramon, also near the Calaveras Fault, in October 2015 (Xue et al, 2018). Engineers moved 12 million cubic yards of earth and rock to make room for and build the new dam. “Swarms may indicate other activity in the area,” said Burgmann. It is one of the fastest creeping fault segments in the San Francisco Bay Region. We suggest that Zone V fails only … Final Technical Report to US Geological Survey, National Earthquake Hazards Reduction Program. In 1979, the 5.7M Coyote Lake Earthquake ruptured to the south of the 1984 and 1911 earthquakes. Journal of Geophysical Research: Solid Earth, 101(B3), 5961-5975. They came one after the other along the Calaveras Fault in Santa Clara County. The fault divides into three segments, each with different characteristics and a different degree of earthquake risk. He noted that there have been several large earthquakes linked to construction of dams and reservoirs in India and Egypt. As far as dam safety, the SFPUC confirmed that there were “no impacts at all to the dam or its surrounding facilities” following any earthquakes in this swarm. It produced the October 30, 2007 … With a slip rate of about 15 mm/yr (0.6 in/yr) and a length of about 100 km (60 mi), the Calaveras is highly active and certainly capable of a M7+ earthquake. The Calaveras fault here is unusual because it creeps, moving a few millimeters per year, instead of storing up energy and releasing it all in a big earthquake. More than 35 quakes ranging as high as a magnitude-3.5 have been recorded by the U.S. Geological Survey since September 27. Geodetic monitoring of the Calaveras fault near this location indicates about 6 mm/yr (0.24 inches/year), but further south near Hollister the … 1996). This means having an emergency kit and plan, securing your contents, retrofitting an older home, and considering insurance. 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