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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. 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. 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. Earthquake swarms usually end without a major event and generally die out within days to months. 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. It produced the October 30, 2007 … This means having an emergency kit and plan, securing your contents, retrofitting an older home, and considering insurance. Within a minute, it was followed by a 3.6-magnitude quake along the Calaveras Fault in Santa Clara County. The fault cuts through the towns of Walnut Creek, San Ramon, Dublin, Pleasanton, Sunol, and Hollister. The Hayward Fault splinters from the Calaveras Fault, which itself is an offshoot of the The Hayward Fault runs from San Pablo Bay to Fremont. The Calaveras Fault and lost seismograms . 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. They came one after the other 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. Final Technical Report to US Geological Survey, National Earthquake Hazards Reduction Program. Credit: Dicklyon (CC BY-SA 4.0). Some scientists predict that the Bay Area's the next major quake will occur on this 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. Construction on the new Calaveras Dam exposed faults not previously mapped. Swarms likely light up portions of faults that suddenly begin to creep—or slip at a much higher rate than usual. The slip rate along the fault … 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. 8, Calaveras Dam Replacement Project. The white lines indicate faults recognized by the USGS. That makes it a favorite laboratory for Earth Scientists and students to see faulting in slow-motion. The reservoir sits atop a major branch of the San Andreas Fault system called the Calaveras Fault. In Hollister the Calaveras Fault is displaying aseismic motion—one side of the fault is slipping past the other side of … Both occurred on Oppenheimer et al. Construction on a new earth-and-rock-fill dam began in 2011 and was completed in May 2019, according to the SFPUC. California Geological Survey 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. 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. But “they always cause discussion and debate,” said Burgmann. It is one of the fastest creeping fault segments in the San Francisco Bay Region. 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. Over 70 small quakes have struck beneath Observation Hill since mid-August. 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. “We really don’t know what causes an earthquake swarm,” said Roland Burgmann, a geologist at the University of California-Berkeley. 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 initial earthquake Calaveras Dam is located on the left (north) edge of the reservoir in the photograph. Small quakes do occur here, but not large-displacement earthquakes. 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. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal). The San Andreas Fault is a continental transform fault that extends roughly 1,200 kilometers (750 mi) through California. Within a minute, it was followed by a magnitude 3.6 quake along the Calaveras Fault in Santa Clara County. 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 Most faults do not creep at all, but parts of the San Andreas, Hayward and Calaveras all do. If you live or work in the East Bay, this is the time to ask yourself if you are quake ready. It struck along the Calaveras Fault and had a depth of 7.4 kilometers, according to the USGS. A magnitude 3.7 earthquake was reported Tuesday morning 2 miles from Morgan Hill, according to the U.S. Geological Survey. USGS These shallow repeaters align well … 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 quake was reported at 10:35 a.m. and was centered east of Alum Rock Park. 1996). During the past week, 75 quakes have rattled the beautiful town of Danville, scene of the beloved Robin Williams movie, “Mrs. We use specialized high … 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. More than 35 quakes ranging as high as a magnitude-3.5 have been recorded by the U.S. Geological Survey since September 27. This is a relief to the 27 million residents who rely on the Calaveras Reservoir. Holocene slip rate and earthquake recurrence of the northern Calaveras fault at Leyden Creek, northern California. Amer., 99, 1746–1759, doi: 10.1785/0120080305 This article has been updated to reflect recent earthquakes in the swarm. 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. The U.S. Geological Survey (USGS) publishes updated frequency and severity likelihood every six years for the entire U.S. There are several reasons why these earthquakes may be occurring here. It’s the latest quake in an ongoing swarm that started ramping up on August 17, 2020. “Swarms may indicate other activity in the area,” said Burgmann. Calaveras County, CA has a moderate earthquake risk, with a total of 1 earthquakes since 1931. 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. 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. Kelson, K. I., & Sundermann, S. T. (2007). 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… 's (1990) Zone V "stuck patch" on the central Calaveras fault, providing new support for their model of Calaveras fault earthquake activity. Engineers moved 12 million cubic yards of earth and rock to make room for and build the new dam. The first quake was reported at 6:58 a.m. 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. Nevertheless, should this swarm penetrate the Calaveras Fault, the chances of a larger shock will climb, and the monitoring vigilance will intensify. are the most studied and understood fault systems in the world. 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. The 2003 Working Group Report divided the fault into three segments. The Calaveras Fault is a mostly right-lateral, strike-slip fault. The Calaveras fault produced the M6.2 Morgan Hill Earthquake in 1984. 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 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. In 1979, the 5.7M Coyote Lake Earthquake ruptured to the south of the 1984 and 1911 earthquakes. 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. Most likely, the earthquakes are simply releasing built-up stress due to the ongoing motion along the Calaveras Fault, Harlan says. The earthquake faults in California, including the Hayward, the Calaveras and the San Andreas faults. 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). During excavation of Observation Hill, faults that had never before been mapped as … “I think the swarm is just a good reminder of seismic hazard that exists along the fault.”. It's a kind of "Faults For Dummies!" In this study, we greatly improve the earthquake locations on the Calaveras Fault. On 6 August 1979, a magnitude 5.7 earthquake occurred along the Calaveras fault zone in the Coyote Lake area of central California. Hayward-Calaveras fault zone (HCFZ), characterization of the creep rates along the faults with a high spatial resolution is necessary. The fault divides into three segments, each with different characteristics and a different degree of earthquake risk. Witter, R. C., Kelson, K. I., Barron, A. D., & Sundermann, S. T. (2003). 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 … 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. Soc. He noted that there have been several large earthquakes linked to construction of dams and reservoirs in India and Egypt. 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