The Mount Diablo Thrust Fault, also known as the Mount Diablo Blind Thrust, is a thrust fault in the vicinity of Mount Diablo in Contra Costa County, California. The fault lies between the Calaveras Fault, the Greenville Fault, and the Concord Fault, all right-lateral strike-slip faults, and appears to transfer movement from the Calaveras and Greenville Faults to the Concord Fault, while continuing to uplift Mount Diablo.
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. 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 borders the North American Plate along a transform boundary, the San Andreas Fault. The westward component of the North American Plate's motion and the irregularity of the San Andreas Fault results in some compressive force along the San Andreas and its associated faults, thus helping lift the Coast Ranges. The Mount Diablo Thrust Fault and the Great Valley Blind Thrust faults are consequences of this compression.
Movement along the Mount Diablo Thrust Fault includes crustal shortening of about 2.6 mm and uplift of about 1 mm per year. [1]
The Mount Diablo Thrust Fault is approximately 25 km long, and dips at an angle of 38 degrees to the northeast. The Mount Diablo Thrust Fault is capable of generating an earthquake of magnitude MW=6.7. The predicted rupture surface begins 8 km below the surface, and there is thus no surface expression of the fault, and a low likelihood of surface rupture in the event of a large earthquake on the fault. No large historic earthquakes are known to have occurred on the Mount Diablo Thrust Fault. The recurrence interval for large earthquakes along the fault is predicted to be about 400 years. [2]
Compressive stresses are produced by offset and converging slip-strike motions between the Calaveras Fault and the Clayton-Marsh Creek-Greenville Fault which manifest in the Mount Diablo Thrust Fault. [3]
The Mount Diablo Thrust Fault underlays several cities and unincorporated communities in Contra Costa County: Alamo, Antioch, Blackhawk, Brentwood, Clayton, Concord, Danville, Diablo, San Ramon, and Walnut Creek. [4]
An earthquake – also called a quake, tremor, or temblor – is the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they cannot be felt, to those violent enough to propel objects and people into the air, damage critical infrastructure, and wreak destruction across entire cities. The seismic activity of an area is the frequency, type, and size of earthquakes experienced over a particular time. The seismicity at a particular location in the Earth is the average rate of seismic energy release per unit volume.
The San Andreas Fault is a continental right-lateral strike-slip transform fault that extends roughly 1,200 kilometers (750 mi) through the U.S. state of California. It forms part of the tectonic boundary between the Pacific Plate and the North American Plate. Traditionally, for scientific purposes, the fault has been classified into three main segments, each with different characteristics and a different degree of earthquake risk. The average slip rate along the entire fault ranges from 20 to 35 mm per year.
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as the megathrust faults of subduction zones or transform faults. Energy release associated with rapid movement on active faults is the cause of most earthquakes. Faults may also displace slowly, by aseismic creep.
A blind thrust earthquake occurs along a thrust fault that does not show signs on the Earth's surface, hence the designation "blind". Such faults, being invisible at the surface, have not been mapped by standard surface geological mapping. Sometimes they are discovered as a by-product of oil exploration seismology; in other cases their existence is not suspected.
The Hayward Fault Zone is a right-lateral strike-slip geologic fault zone capable of generating destructive earthquakes. The fault was first named in the Lawson Report of the 1906 San Francisco Earthquake in recognition of its involvement in the earthquake of 1868. This fault is about 119 km (74 mi) long, situated mainly along the western base of the hills on the east side of San Francisco Bay. It runs through densely populated areas, including Richmond, El Cerrito, Berkeley, Oakland, San Leandro, Castro Valley, Hayward, Union City, Fremont, and San Jose.
The 1857 Fort Tejon earthquake occurred at about 8:20 a.m. on January 9 in central and Southern California. One of the largest recorded earthquakes in the United States, with an estimated moment magnitude of 7.9, it ruptured the southern part of the San Andreas Fault for a length of about 225 miles, between Parkfield and Wrightwood.
In geology, aseismic creep or fault creep is measurable surface displacement along a fault in the absence of notable earthquakes. Aseismic creep may also occur as "after-slip" days to years after an earthquake. Notable examples of aseismic slip include faults in California.
The Mendocino Triple Junction (MTJ) is the point where the Gorda plate, the North American plate, and the Pacific plate meet, in the Pacific Ocean near Cape Mendocino in northern California. This triple junction is the location of a change in the broad tectonic plate motions which dominate the west coast of North America, linking convergence of the northern Cascadia subduction zone and translation of the southern San Andreas Fault system. This region can be characterized by transform fault movement, the San Andreas also by transform strike slip movement, and the Cascadia subduction zone by a convergent plate boundary subduction movement. The Gorda plate is subducting, towards N50ºE, under the North American plate at 2.5–3 cm/yr, and is simultaneously converging obliquely against the Pacific plate at a rate of 5 cm/yr in the direction N115ºE. The accommodation of this plate configuration results in a transform boundary along the Mendocino Fracture Zone, and a divergent boundary at the Gorda Ridge. This area is tectonically active historically and today. The Cascadia subduction zone is known to be capable of producing megathrust earthquakes on the order of MW 9.0.
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.
The Clayton-Marsh Creek-Greenville Fault is a fault located in the eastern San Francisco Bay Area of California, in Alameda County and Contra Costa County. It is part of the somewhat parallel system of faults that are secondary to the San Andreas Fault.
The San Jacinto Fault Zone (SJFZ) is a major strike-slip fault zone that runs through San Bernardino, Riverside, San Diego, and Imperial Counties in Southern California. The SJFZ is a component of the larger San Andreas transform system and is considered to be the most seismically active fault zone in the area. Together they relieve the majority of the stress between the Pacific and North American tectonic plates.
The 1992 Cape Mendocino earthquakes occurred along the Lost Coast of Northern California on April 25 and 26. The three largest events were the M7.2 thrust mainshock that struck near the unincorporated community of Petrolia midday on April 25 and two primary strike-slip aftershocks measuring 6.5 and 6.6 that followed early the next morning. The sequence encompassed both interplate and intraplate activity that was associated with the Mendocino Triple Junction, a complex system of three major faults that converge near Cape Mendocino. The total number of aftershocks that followed the events exceeded 2,000.
The Marlborough fault system is a set of four large dextral strike-slip faults and other related structures in the northern part of South Island, New Zealand, which transfer displacement between the mainly transform plate boundary of the Alpine fault and the mainly destructive boundary of the Kermadec Trench, and together form the boundary between the Australian and Pacific Plates.
The 1991 Sierra Madre earthquake occurred on June 28 at 07:43:55 local time with a moment magnitude of 5.6 and a maximum Mercalli intensity of VII. The thrust earthquake resulted in two deaths, around 100 injuries, and damage estimated at $33.5–40 million. The event occurred beneath the San Gabriel Mountains on the Clamshell–Sawpit Fault, which is a part of the Sierra Madre–Cucamonga Fault System. Instruments captured the event at a number of strong motion stations in Southern California.
The 1979 Coyote Lake earthquake occurred at 10:05:24 local time on August 6 with a moment magnitude of 5.7 and a maximum Mercalli Intensity of VII. The shock occurred on the Calaveras Fault near Coyote Lake in Santa Clara County, California and resulted in a number of injuries, including some that required hospitalization. Most of the $500,000 in damage that was caused was non-structural, but several businesses were closed for repairs. Data from numerous strong motion instruments was used to determine the type, depth, and extent of slip. A non-destructive aftershock sequence that lasted throughout the remainder of the month was of interest to seismologists, especially with regard to fault creep, and following the event local governments evaluated their response to the incident.
The 1892 Vacaville–Winters earthquakes occurred in northern California as a large doublet on April 19 and April 21. Measured on a seismic scale that is based on an isoseismal map or the event's felt area, the 6.4 Mla and 6.2 Mla events were assigned a maximum Mercalli intensity of IX (Violent), and affected the North Bay and Central Valley areas. The total damage was estimated to be between $225,000 and 250,000 and one person was killed. No evidence of fault movement on the surface of the ground was observed as a result of either of the strong shocks. Both occurred in the domain of the San Andreas strike-slip system of faults, but their focal mechanism is uncertain.
The 1812 Ventura earthquake occurred on the morning of December 21 at 11:00 Pacific Standard Time (PST). The Mw 7.1 earthquake, with a Modified Mercalli intensity scale rating of X (Extreme), along with its resulting tsunami, caused considerable damage to present-day Santa Barbara and Ventura County, California, which was at the time a territory of the Spanish Empire. One person was killed as a result of the earthquake while another from the aftershock. The earthquake occurred just as the region was recovering from another event on December 8. Both events are thought to have been related.
The 1654 Tianshui earthquake occurred on July 21 in Tianshui, Gansu Province, Ming dynasty sometime between 21:00 and 23:00 local time. The event had an estimated moment magnitude of 7.0 and was assigned a maximum intensity of XI on the China seismic intensity scale. Resulting in extreme damage and affecting at least four provinces, the quake killed approximately 30,000 people.
The 1923 Renda earthquake occurred on March 24 at 20:40 local time between the counties of Daofu and Luhuo in Sichuan, China. The estimated Ms 7.3 earthquake was assigned a maximum modified Mercalli intensity scale rating of X (Extreme). Severe damage occurred in Sichuan, killing an estimated 4,800 people.
The earthquake cycle refers to the phenomenon that earthquakes repeatedly occur on the same fault as the result of continual stress accumulation and periodic stress release. Earthquake cycles can occur on a variety of faults including subduction zones and continental faults. Depending on the size of the earthquake, an earthquake cycle can last decades, centuries, or longer. The Parkfield portion of the San Andreas fault is a well-known example where similarly located M6.0 earthquakes have been instrumentally recorded every 30–40 years.
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