A series of small earthquakes near the recently built Calaveras Dam replacement is a reminder of the significant seismic hazard at the new dam site. It is one of the fastest creeping fault segments in the San Francisco Bay Region. While … In 1979, the 5.7M Coyote Lake Earthquake ruptured to the south of the 1984 and 1911 earthquakes. 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. are the most studied and understood fault systems in the world. Within a minute, it was followed by a 3.6-magnitude quake along the Calaveras Fault in Santa Clara County. In Hollister the Calaveras Fault is displaying aseismic motion—one side of the fault is slipping past the other side of … 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. Kelson, K. I., & Sundermann, S. T. (2007). The first quake was reported at 6:58 a.m. 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. Journal of Geophysical Research: Solid Earth, 101(B3), 5961-5975. 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 … 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). Those studies indicate timing of the most recent large earthquake is poorly constrained but suggest an average interval between surface rupturing earthquakes of 250 to 850 years, highlighting the uncertainty in what seismologists call the “recurrence interval” of major earthquakes. These shallow repeaters align well … The San Andreas Fault is a continental transform fault that extends roughly 1,200 kilometers (750 mi) through California. PUSH (Probabilistic Uniform Seismic Hazard), http://temblor.net/earthquake-insights/calaveras-535/, When preparing for earthquakes, don’t forget the small ones, American Geophysical Union meeting brings student research to light, Surface deformation observed in moderate Greek quake. 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. The fault divides into three segments, each with different characteristics and a different degree of earthquake risk. The Calaveras Fault is a mostly right-lateral, strike-slip fault. It's a kind of "Faults For Dummies!" Two 3.4 magnitude earthquakes struck hours apart in the same area in Northern California on Sunday, according to officials. We suggest that Zone V fails only … At that time, most U.S. seismic observatories were run by scientist priests at Jesuit universities. Monitoring Velocity Variations in the Crust Using Earthquake Doublets: An Application to the Calaveras Fault, California July 1984 Journal of Geophysical Research Atmospheres 89:5719-5731 They came one after the other along the Calaveras Fault in Santa Clara County. In this study, we greatly improve the earthquake locations on the Calaveras Fault. 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. Two minutes after 9 a.m., a third earthquake hit, registering a magnitude of 3.3 at a depth 4.3 km. SAN JOSE (KRON) — Two earthquakes shook the South Bay on Tuesday morning. The quake was reported at 10:35 a.m. and was centered east of Alum Rock Park. Details of the 3D fault geometry at stepovers and bends—particularly in urban settings—are often lacking, limiting efforts to constrain hazard calculations in these areas. The 2003 Working Group Report divided the fault into three segments. 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). But by the time these professors began to die in mid-century, their lifelong seismogram archives were thrown out. Neither is construction of the dam itself, because excavated material was not removed from the site, but instead only shifted around over a small area, Burgmann said. It’s the latest quake in an ongoing swarm that started ramping up on August 17, 2020. Most faults do not creep at all, but parts of the San Andreas, Hayward and Calaveras all do. The fault cuts through the towns of Walnut Creek, San Ramon, Dublin, Pleasanton, Sunol, and Hollister. During excavation of Observation Hill, faults that had never before been mapped as … Lian Xue, Roland Bürgmann , David R. Shelly, Christopher W. Johnson, Taka’aki Taira (2018), Kinematics of the 2015 San Ramon, California earthquake swarm: Implications for fault zone structure and driving mechanisms, in press, Earth and Planetary Science Letters. This earthquake and its aftershocks took place within a very dense seismic network. It is also being subducted far to the northwest into the Aleutian Trench. Our ability to resolve fault zone structure and hence to address many essential aspects of earthquake behavior, is limited by our ability to obtain precise earthquake locations. Nevertheless, should this swarm penetrate the Calaveras Fault, the chances of a larger shock will climb, and the monitoring vigilance will intensify. Studies conducted in the late 1990s indicated that the original dam, which was built in 1919, didn’t meet seismic safety standards given its construction and proximity to the nearby Calaveras Fault. Geodetic monitoring of the Calaveras fault near this location indicates about 6 mm/yr (0.24 inches/year), but further south near Hollister the … 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. 8, Calaveras Dam Replacement Project. Hayward-Calaveras fault zone (HCFZ), characterization of the creep rates along the faults with a high spatial resolution is necessary. The Calaveras fault produced the M6.2 Morgan Hill Earthquake in 1984. More than 35 quakes ranging as high as a magnitude-3.5 have been recorded by the U.S. Geological Survey since September 27. Earthquake Information for Calaveras County, California. Only one 1911 seismogram from the U.S. survived, from the University of St. Louis, which was saved … 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. We use specialized high … The largest historical quake on the Calaveras Fault was a M=6.6 event in 1911 (Doser, 2009), but far too … However, the rms residuals for P-wave arrivals at many of the network stations were as high as 0.25 sec due to the laterally heterogeneous structure of this area which deviates from the … 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. Construction on the new Calaveras Dam was completed last year. “As I understand it, the excavated material [at Calaveras] was mostly put back into the nearby new dam embankment,” he said. Doser, Diane I., Kim B. Olsen, Fred F. Pollitz, Ross S. Stein, and Shinji Toda (2009), The 1911 M∼6.6 Calaveras earthquake: Source parameters and the role of static, viscoelastic, and dynamic Coulomb stress changes imparted by the 1906 San Francisco earthquake, Bull.Seismol. 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. That makes it a favorite laboratory for Earth Scientists and students to see faulting in slow-motion. 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. Some 600 quakes struck San Ramon, also near the Calaveras Fault, in October 2015 (Xue et al, 2018). The Calaveras and Hayward faults extend up the east side of the San Francisco Bay. This article has been updated to reflect recent earthquakes in the swarm. When full, it can store 96,850 acre-feet, or 31 billion gallons of water. future moderate earthquakes on the Calaveras Fault. 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. The dam design was modified to ensure it could accommodate small amounts of movement on these secondary faults, which might be triggered by a large local earthquake on the main Calaveras fault nearby, according to a United States Society on Dams report. Small quakes do occur here, but not large-displacement earthquakes. The Bay Area fault system and the spot (red star) where the Hayward Fault branches off from the Calaveras Fault. USSD Dams and Levees Bulletin of the United States Society on Dams Summer 2019 Issue No. ... Like all of California, the Central Valley—which is ringed by faults—is earthquake country. The slip rate along the fault … 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. This is a relief to the 27 million residents who rely on the Calaveras Reservoir. The white lines … A 3.6-magnitude earthquake was reported Wednesday morning east of San Jose, according to the U.S. Geological Survey. Although most of the quakes in this week’s swarm are 3-5 km (2-3 mi) from the Calaveras Fault, the swarm has been migrating toward the Calaveras over the past few days. It produced the October 30, 2007 … Credit: SFPUC. It passes through parts of Berkeley, Oakland, Hayward and Fremont before branching into a set of surface faults that connect it to the central part of the Calaveras Fault, according to the USGS. 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. A magnitude 3.7 earthquake was reported Tuesday morning 2 miles from Morgan Hill, according to the U.S. Geological Survey. 's (1990) Zone V "stuck patch" on the central Calaveras fault, providing new support for their model of Calaveras fault earthquake activity. The reservoir is located less than 20 miles from where Tesla is based in Fremont, California, and sits on the Calaveras fault system. Witter, R. C., Kelson, K. I., Barron, A. D., & Sundermann, S. T. (2003). Swarms likely light up portions of faults that suddenly begin to creep—or slip at a much higher rate than usual. Final Technical Report to US Geological Survey, National Earthquake Hazards Reduction Program. Within a minute, it was followed by a magnitude 3.6 quake along the Calaveras Fault in Santa Clara County. The Calaveras fault system runs over 80 miles, from south of Hollister into the Danville-Walnut Creek area. 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. The earthquake faults in California, including the Hayward, the Calaveras and the San Andreas faults. At that time, most U.S. seismic observatories were run by scientist priests at Jesuit universities. The Calaveras Fault and lost seismograms . 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 Hayward Fault splinters from the Calaveras Fault, which itself is an offshoot of the Fault connectivity defines the maximum earthquake rupture length, and the three-dimensional (3D) geometry of faults affects the dynamics of fault rupture, slip, and ground motion (11–15). Risk … There are several reasons why these earthquakes may be occurring here. The largest historical quake on the Calaveras Fault was a M=6.6 event in 1911 (Doser, 2009), but far too little is known about this large event. The reservoir sits atop a major branch of the San Andreas Fault system called the Calaveras Fault. “There could be fluids in the fault zone, for example.” He suggested there might be areas of geothermal activity in the fault zone, as well. Over 70 quakes have struck in the area around the Calaveras Dam since mid-August. California Geological Survey 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. If you live or work in the East Bay, this is the time to ask yourself if you are quake ready. 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. It struck along the Calaveras Fault and had a depth of 7.4 kilometers, according to the USGS. USGS The fault cuts through the towns of Walnut Creek, San Ramon, Dublin, Pleasanton, Sunol, and Hollister. window.dojoRequire(["mojo/signup-forms/Loader"], function(L) { L.start({"baseUrl":"mc.us11.list-manage.com","uuid":"b739709487a9092b101e207ed","lid":"197a65374d","uniqueMethods":true}) }), PUSH (Probabilistic Uniform Seismic Hazard), Construction on a new earth-and-rock-fill dam, linked to construction of dams and reservoirs, When preparing for earthquakes, don’t forget the small ones, American Geophysical Union meeting brings student research to light, Surface deformation observed in moderate Greek quake. 1996). 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. In California, the plate is sliding northwestward along a transform boundary, the San Andreas Fault, toward the subduction zone. Calaveras County, CA has a moderate earthquake risk, with a total of 1 earthquakes since 1931. Credit: Rick Harlan (used with permission of SFPUC). This means having an emergency kit and plan, securing your contents, retrofitting an older home, and considering insurance. Most likely, the earthquakes are simply releasing built-up stress due to the ongoing motion along the Calaveras Fault, Harlan says. Why faults start and stop creeping is a mystery, but most swarms and creep events do not cascade into larger earthquakes. It is unclear on which faults these quakes are occurring, but this activity is a sign that the area is anything but quiet. During the past week, 75 quakes have rattled the beautiful town of Danville, scene of the beloved Robin Williams movie, “Mrs. This system forms the plate tectonic boundary between the North American Plate and the Pacific Plate. But “they always cause discussion and debate,” said Burgmann. The new dam was designed to withstand a magnitude-7.25 earthquake. Both occurred on Oppenheimer et al. 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 … “I think the swarm is just a good reminder of seismic hazard that exists along the fault.”. The San Andreas fault system is the … The white lines indicate faults recognized by the USGS. Earthquake swarms usually end without a major event and generally die out within days to months. 178, pg. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal). 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. [4] The geometry of fault zones within the Earth is revealed primarily by seismicity. 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. 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. Calaveras Dam is located on the left (north) edge of the reservoir in the photograph. He noted that there have been several large earthquakes linked to construction of dams and reservoirs in India and Egypt. Although the area has seen little significant seismic activity over the past 100 years, paleoseismic studies at Leyden Creek about one mile (2 kilometers) north of the dam indicate that this section of the northern Calaveras fault has generated a number of ground rupturing earthquakes of possibly up to around magnitude-7.0 over the last 2,500 years (Kelson et al. “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. Over 70 small quakes have struck beneath Observation Hill since mid-August. During excavation of Observation Hill, faults that had never before been mapped as well as several previously unrecognized landslides were discovered in the planned foundation area of the new dam. “We really don’t know what causes an earthquake swarm,” said Roland Burgmann, a geologist at the University of California-Berkeley. Shaking can begin suddenly but have lasting impacts. But by the time these professors began to die in mid-century, their lifelong seismogram archives were—inconceivably and unconscionably—thrown out. Kelson, K. I., Simpson, G. D., Lettis, W. R., & Haraden, C. C. (1996). At the same time, the North American Plateis moving southwestward relative to the Earth's core, but southeastward relative to the Pacific Plate, due to the latter's much faste… On 6 August 1979, a magnitude 5.7 earthquake occurred along the Calaveras fault zone in the Coyote Lake area of central California. Soc. The Calaveras reservoir provides drinking water storage for residents throughout California, according to the San Francisco Public Utilities Commission (SFPUC), who manages the reservoir. Earthquake scientists are far more worried about the potential violence of a more northern stretch of the Calaveras Fault, between the towns of Danville and San Ramon. That is enough to fill Levi’s Stadium from bottom to top four times, according to SFPUC. The Hayward Fault runs from San Pablo Bay to Fremont. Credit: Dicklyon (CC BY-SA 4.0). Construction on the new Calaveras Dam exposed faults not previously mapped. Map of active fault traces, geomorphic features and Quaternary surficial deposits along the Central Calaveras fault, Santa Clara County, California. Repeating earthquakes can be grouped in three categories: 1) small cumulative slip and medium depths (3-7 km), characteristic of the northern Hayward fault; 2) large cumulative slip and medium to large depths (3-11 km), characteristic of the Calaveras fault; and shallow events (less than 3 km), occurring only at the junction between the Hayward and Calaveras faults. 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. The San Andreas fault system is to the west, the Garlock fault is to the south and the faults of the Sierra Nevada are to the east. 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. The similarity of seismograms recorded by two seismic stations demonstrate that the 31 October 2007 moment magnitude M5.4 Alum Rock earthquake is a repeat of a 1955 M L 5.5 earthquake. Most researchers believe that strain accumulated along the Calaveras south of Calaveras Reservoir is transferred to the Hayward fault on the Mission Hills fault (Oppenheimer and Macgregor, 1991). Construction on a new earth-and-rock-fill dam began in 2011 and was completed in May 2019, according to the SFPUC. Some scientists predict that the Bay Area's the next major quake will occur on this fault. The largest historical quake on the Calaveras Fault was a M6.6 earthquake in 1911. 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 … Excavated areas were extensively mapped to maintain a precise record of the geologic features in the subsurface that could affect the new dam’s seismic resilience. Amer., 99, 1746–1759, doi: 10.1785/0120080305 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. Despite the apparent lessened activity on the northernmost trace of the Calaveras, it does appear to have spawned a Magnitude 6.9 earthquake on July 3, 1861, causing continuous ground rupture, 6-8 miles … 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. 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