Hayward Fault Zone
The Hayward Fault Zone is a geologic fault zone capable of generating destructive earthquakes. This fault is about 74 mi long, situated 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, Oakland, San Leandro, Castro Valley, Union City and San Jose. The Hayward Fault is parallel to the San Andreas Fault, which lies offshore and through the San Francisco Peninsula. To the east of the Hayward lies the Calaveras Fault. In 2007 the Hayward Fault was discovered to merge with the Calaveras Fault east of San Jose at a depth of 4 miles, with the potential of creating earthquakes much larger than expected; some geologists have suggested that the Southern Calaveras should be renamed as the Southern Hayward. North of San Pablo Bay is the Rodgers Creek Fault, shown in 2016 to be linked with the Hayward Fault under San Pablo Bay to form a combined Hayward-Rodgers Creek Fault, 118 miles long, stretching from north of Healdsburg through Santa Rosa down to Alum Rock in San Jose.
Another fault further north, the Maacama Fault, is considered to be part of the "Hayward Fault subsystem". While the San Andreas Fault is the principal transform boundary between the Pacific Plate and the North American Plate, the Hayward-Rodgers Creek Fault takes up its share of the overall displacement of the two plates; the Pacific Plate is a major section of the Earth's crust expanding by the eruption of magma along the East Pacific Rise to the southeast. It is being subducted far to the northwest into the Aleutian Trench. 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 relative to the Earth's core, but southeastward relative to the Pacific Plate, due to the latter's much faster northwestward motion; the westward component of the North American Plate's motion results in some compressive force along the San Andreas and its associated faults, thus helping lift the Pacific Coast Ranges and other parallel inland ranges to the west of the Central Valley, in this region most notably the Diablo Range.
The Hayward Fault shares the same relative motions of the San Andreas. As with portions of other faults, a large extent of the Hayward Fault trace is formed from a narrow complex zone of deformation which can span hundreds of feet in width; the transform boundary defined by the San Andreas Fault is not straight, the stresses between the Pacific and North American Plates are diffused over a wide region of the West, extending as far as the eastern side of the Sierra Nevada Mountains. The Hayward Fault is one of the secondary faults in this diffuse zone, along with the Calaveras Fault to the east and the San Gregorio Fault, west of the San Andreas; the complete fault zone, including the Rodgers Creek fault, is divided by seismologists into three segments – Rodgers Creek, Northern Hayward, Southern Hayward. It is expected that these segments may fail singly or in adjacent pairs, creating earthquakes of varying magnitude; the Association of Bay Area Governments in concert with other government agencies has sponsored the analysis of local conditions and the preparation of maps indicative of the destructive potential of these earthquakes.
The various ABAG maps shown below represent some of the more possible combinations. While there are indications that a substantial earthquake on a nearby parallel fault can release stress and so decrease the near-term probability of an earthquake, the opposite appears to be true concerning sequential segments. A release on a major segment can increase the likelihood of an earthquake on an adjacent fault segment, increasing the likelihood of two major regional earthquakes within a period of a few months; the connection between the Rodgers Creek Fault Zone and the Hayward Fault Zone was unclear until 2015 when a survey of the floor of San Pablo Bay found that the ends of the two faults were smoothly linked between Point Pinole and Lower Tubbs Island. An alternate prior hypothesis suggested that the Hayward Fault and Rodgers Creek Fault were connected by a series of en echelon fault strands beneath San Pablo Bay; the new finding means that the Rodgers-Hayward system together could produce a quake with a magnitude as high as 7.2.
It is considered possible that a major seismic event on either fault may involve movement on the other, either concurrently or within an interval of up to several months. The Association of Bay Area Governments has prepared ground shaking maps that include a possible concurrent scenario. In October 2016, scientists found definitive evidence that the Rodgers Creek Fault and the Hayward Fault are linked together under San Pablo Bay. A simultaneous rupture of the connected Hayward-Rodgers Creek Fault – about 118 mi long from just north of Healdsburg down to Alum Rock in San Jose – could result in a major earthquake of magnitude 7.4 that "would cause extensive damage and loss of life with global economic impact". It has been suggested that the name "Rodgers Creek Fault" be retired and that the entire 118 mi fault be known as the "Hayward Fault"; the Calaveras Fault is continuous from the Sunol area south to Hollister. It was long believed that there was no connection between the Hayward Fault and the Calaveras, but geological studies suggest that the two may be connected.
If true, this link 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 ruptur
The Seattle Fault is a zone of multiple shallow east-west thrust faults that cross the Puget Sound Lowland and through Seattle in the vicinity of Interstate Highway 90. The Seattle Fault was first recognized as a significant seismic hazard in 1992, when a set of reports showed that about 1,100 years ago it was the scene of a major earthquake of about magnitude 7 – an event that entered Native American oral legend. Extensive research has since shown the Seattle Fault to be part of a regional system of faults. First suspected from mapping of gravitational anomalies in 1965 and an uplifted marine terrace at Restoration Point, the Seattle Fault's existence and hazard were established by a set of five reports published in Science in 1992; these reports looked at the timing of abrupt uplift and subsidence around Restoration Point and Alki Point, tsunami deposits on Puget Sound, turbidity in lake paleosediments, rock avalanches, multiple landslides around Lake Washington, determined that all these happened about 1100 years ago, most due to an earthquake of magnitude 7 or greater on the Seattle Fault.
Although the 900–930 CE earthquake was over a thousand years ago, local native legends have preserved an association of a powerful supernatural spirit – a'yahos, noted for shaking, rushes of water, landsliding – with five locales along the trace of the Seattle Fault, including a "spirit boulder" called Psai-Yah-hus near the Fauntleroy ferry dock in West Seattle. The Seattle Fault is the structural boundary where 50–60 millions of years old basalt of the Crescent Formation on the south has been uplifted – the Seattle Uplift – and is tipping into the Seattle Basin, where the Tertiary bedrock is buried under at least 7 km of softer, lighter sedimentary strata of the younger Blakeley and Blakely Harbor formations; this has resulted in a 4 to 7 km wide zone of complex faulting, with three or more main south-dipping thrust faults. Most of the faulting is "blind", difficult to locate because of the heavy vegetation or development. Three principal strands have been identified, their location determined by high-resolution seismic reflection and aeromagnetic surveys.
The northernmost strand lies nearly along Interstate 90 and under Lake Sammamish. The central section of the fault zone – where it crosses the apparent location of the Olympic-Wallowa Lineament – shows marked variation in the location of the strands and of the underlying structure, but the nature and significance of this is not understood; the fault extends for 70 km from near Fall City on the east, where it appears to be terminated by the South Whidbey Island Fault, to Hood Canal on the west. However, boundaries defining the western termination zone is unclear, it is the northern edge of the Seattle Uplift. One model has the Seattle and Tacoma faults converging at depth to form a wedge, being popped up by north–south oriented compression that derives from plate tectonics. Another model interprets the Seattle Uplift as a sheet of rock, being forced up a ramp. Subsequent work suggests that the structure of the Seattle Fault may vary from east to west, with both models being applicable in different sections.
A model has part of the north-thrusting sheet forming a wedge between the sedimentary formations of the Seattle Basin and the underlying bedrock. The Seattle Fault is believed to date from about 40 million years ago; this is about the time that the strike-slip movement on the north-striking Straight Creek Fault to the east ceased, due to the intrusions of plutons. It appears that when the Straight Creek Fault became stuck the north–south compressive force that it had accommodated by strike-slip motion was transferred to the crust of the Puget Lowland, which subsequently folded and faulted, the various blocks jammed over one another. Other scarps associated with the Seattle fault have been identified by LIDAR-based mapping. Many of the details of the Seattle Fault, including recurrence rate, remain to be resolved. A study of sediments in Lake Washington found evidence of seven large earthquakes in the last 3500 years. Surface scarps due to faulting are observed in this area; this is the site of the West Seattle Fault.
The Seattle Fault is not the only source of earthquake hazard in the Puget Lowland. Other faults in the near surface continental crust, such as the South Whidbey Island Fault, the yet to be studied Olympia Fault, though quiescent, are suspected of generating earthquakes of around magnitude 7. Others, such as the 2001 Nisqually earthquake, originate about 50 to 60 km below Puget Sound in the Benioff zone of the subducting Juan de Fuca Plate, and there are the infrequent but powerful great subduction events, such as the magnitude 9 1700 Cascadia earthquake, where the entire Cascadia subduction zone, from Cape Mendocino to Vancouver Island, slips. But the Seattle and Tacoma faults are the most serious earthquake threat to the populous Seattle–Tacoma area. A 2002 study of br
Basin and Range Province
The Basin and Range Province is a vast physiographic region covering much of the inland Western United States and northwestern Mexico. It is defined by unique basin and range topography, characterized by abrupt changes in elevation, alternating between narrow faulted mountain chains and flat arid valleys or basins; the physiography of the province is the result of tectonic extension that began around 17 million years ago in the early Miocene epoch. The numerous ranges within the province in the United States are collectively referred to as the "Great Basin Ranges", although many are not in the Great Basin. Major ranges include the Snake Range, the Panamint Range, the White Mountains, the Sandia Mountains, the Tetons; the highest point within the province is White Mountain Peak in California, while the lowest point is the Badwater Basin in Death Valley at −282 feet. The province's climate is arid, with numerous ecoregions. Most North American deserts are located within it. Clarence Dutton famously compared the many narrow parallel mountain ranges that distinguish the unique topography of the Basin and Range to an "army of caterpillars marching toward Mexico."
The Basin and Range Province should not be confused with The Great Basin, a sub-section of the greater Basin and Range physiographic region defined by its unique hydrological characteristics. The Basin and Range Province includes much of western North America. In the United States, it is bordered on the west by the eastern fault scarp of the Sierra Nevada and spans over 500 miles to its eastern border marked by the Wasatch Fault, the Colorado Plateau and the Rio Grande Rift; the province extends north to the Columbia Plateau and south as far as the Trans-Mexican Volcanic Belt in Mexico, though the southern boundaries of the Basin and Range are debated. In Mexico, the Basin and Range Province is dominated by and synonymous with the Mexican Plateau. Evidence suggests that the less-recognized southern portion of the province is bounded on the east by the Laramide Thrust Front of the Sierra Madre Oriental and on the west by the Gulf of California and Baja Peninsula with notably less faulting apparent in the Sierra Madre Occidental in the center of the southernmost Basin and Range Province.
Common geographic features include numerous endorheic basins, ephemeral lakes and valleys alternating with mountains. The area is arid and sparsely populated, although there are several major metropolitan areas, such as Las Vegas and Tucson, it is accepted that basin and range topography is the result of extension and thinning of the lithosphere, composed of crust and upper mantle. Extensional environments like the Basin and Range are characterized by listric normal faulting, or faults that level out with depth. Opposing normal faults link at depth producing a horst and graben geometry, where horst refers to the upthrown fault block and graben to the down dropped fault block; the average crustal thickness of the Basin and Range Province is 30 – 35 km and is comparable to extended continental crust around the world. The crust in conjunction with the upper mantle comprises the lithosphere; the base of the lithosphere beneath the Basin and Range is estimated to be about 60 – 70 km. Opinions vary regarding the total extension of the region.
Total lateral displacement in the Basin and Range varies from 60 – 300 km since the onset of extension in the Early Miocene with the southern portion of the province representing a greater degree of displacement than the north. Evidence exists to suggest that extension began in the southern Basin and Range and propagated north over time; the tectonic mechanisms responsible for lithospheric extension in the Basin and Range province are controversial, several competing hypotheses attempt to explain it. Key events preceding Basin and Range extension in the western United States include a long period of compression due to the subduction of the Farallon Plate under the west coast of the North American continental plate which stimulated the thickening of the crust. Most of the pertinent tectonic plate movement associated with the province occurred in Neogene time and continues to the present. By Early Miocene time, much of the Farallon Plate had been consumed, the seafloor spreading ridge that separated the Farallon Plate from the Pacific Plate approached North America.
In the Middle Miocene, the East Pacific Rise was subducted beneath North America ending subduction along this part of the Pacific margin. The movement at this boundary divided the East Pacific Rise and spawned the San Andreas transform fault, generating an oblique strike-slip component. Today, the Pacific Plate moves north-westward relative to North America, a configuration which has given rise to increased shearing along the continental margin; the tectonic activity responsible for the extension in the Basin and Range is a complex and controversial issue among the geoscience community. The most accepted hypothesis suggests that crustal shearing associated with the San Andreas Fault caused spontaneous extensional faulting similar to that seen in the Great Basin. However, plate movement alone does not account for the high elevation of the Range region; the western United States is a region of high heat flow which lowers the density of the lithosphere and stimulates isostatic uplift as a consequence.
Lithospheric regions characterized by elevated heat flow are weak and extensional deformation can occur over a broad region. Basin and Range extension is therefore thought to be unrelated to the kind of extension produced by mantle upw
The Garlock Fault is a left-lateral strike-slip fault running northeast-southwest along the north margins of the Mojave Desert of Southern California, for much of its length along the southern base of the Tehachapi Mountains. The Garlock Fault marks the northern boundary of the area known as the Mojave Block, as well as the southern ends of the Sierra Nevada and the valleys of the westernmost Basin and Range province. Stretching for 250 kilometers, it is the second-longest fault in California and one of the most prominent geological features in the southern part of the state; the Garlock Fault runs from a junction with the San Andreas Fault in the Antelope Valley, eastward to a junction with the Death Valley Fault Zone in the eastern Mojave Desert. It is named after the historic mining town of Garlock, founded in 1894 by Eugene Garlock and now a ghost town; the Garlock Fault is believed to have developed to accommodate the strain between the extensional tectonics of the Great Basin crust and the right lateral strike-slip faulting of the Mojave Desert crust.
Unlike most of the other faults in California, slip on the Garlock Fault is left-lateral. Thus, the terrain north of the fault is moving westward and that on the south is moving eastward; the Garlock Fault moves at a rate of between 2 and 11 mm a year, with an average slip of around 7 millimeters. While most of the fault is locked, certain segments have been shown to move by aseismic creep, motion without resulting earthquakes; the Garlock is not considered to be a active fault producing any shaking detectable by humans, although it has been known to generate sympathetic seismic events when triggered by other earthquakes and in one instance by the removal of ground water. These events, as well as continuing microearthquake activity and the state of the scarps from previous ruptures, do indicate that the Garlock will produce another major quake at some point in the future; the most recent notable event was a magnitude 5.7 near the town of Mojave on July 11, 1992. It is thought to have been triggered by the Landers earthquake, just two weeks earlier.
The last significant ruptures on the Garlock were thought to be in the years 1050 AD and 1500 AD. Research has pinned the interval between significant ruptures on the Garlock as being anywhere between 200 and 3,000 years, depending on the segment of the fault; the Garlock Fault, which constitutes one of the borders of the Mojave Desert, is a significant geologic feature in California. Mountain ranges mark its western edge, its trace is visible on aerial images. Few communities lie directly along the Garlock, as it is situated in the desert, with Frazier Park, Tehachapi and Johannesburg being the closest to it. Southern California Earthquake Data Center: Faults in Southern California
An earthquake is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in size from those that are so weak that they cannot be felt to those violent enough to toss people around and destroy whole cities; the seismicity, or seismic activity, of an area is the frequency and size of earthquakes experienced over a period of time. The word tremor is used for non-earthquake seismic rumbling. At the Earth's surface, earthquakes manifest themselves by shaking and displacing or disrupting the ground; when the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can trigger landslides, volcanic activity. In its most general sense, the word earthquake is used to describe any seismic event—whether natural or caused by humans—that generates seismic waves. Earthquakes are caused by rupture of geological faults, but by other events such as volcanic activity, mine blasts, nuclear tests.
An earthquake's point of initial rupture is called its hypocenter. The epicenter is the point at ground level directly above the hypocenter. Tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane; the sides of a fault move past each other smoothly and aseismically only if there are no irregularities or asperities along the fault surface that increase the frictional resistance. Most fault surfaces do have such asperities and this leads to a form of stick-slip behavior. Once the fault has locked, continued relative motion between the plates leads to increasing stress and therefore, stored strain energy in the volume around the fault surface; this continues until the stress has risen sufficiently to break through the asperity allowing sliding over the locked portion of the fault, releasing the stored energy. This energy is released as a combination of radiated elastic strain seismic waves, frictional heating of the fault surface, cracking of the rock, thus causing an earthquake.
This process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the elastic-rebound theory. It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of the earthquake's energy is used to power the earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat out from the Earth's deep interior. There are three main types of fault, all of which may cause an interplate earthquake: normal and strike-slip. Normal and reverse faulting are examples of dip-slip, where the displacement along the fault is in the direction of dip and movement on them involves a vertical component. Normal faults occur in areas where the crust is being extended such as a divergent boundary. Reverse faults occur in areas.
Strike-slip faults are steep structures where the two sides of the fault slip horizontally past each other. Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip. Reverse faults those along convergent plate boundaries are associated with the most powerful earthquakes, megathrust earthquakes, including all of those of magnitude 8 or more. Strike-slip faults continental transforms, can produce major earthquakes up to about magnitude 8. Earthquakes associated with normal faults are less than magnitude 7. For every unit increase in magnitude, there is a thirtyfold increase in the energy released. For instance, an earthquake of magnitude 6.0 releases 30 times more energy than a 5.0 magnitude earthquake and a 7.0 magnitude earthquake releases 900 times more energy than a 5.0 magnitude of earthquake. An 8.6 magnitude earthquake releases the same amount of energy as 10,000 atomic bombs like those used in World War II. This is so because the energy released in an earthquake, thus its magnitude, is proportional to the area of the fault that ruptures and the stress drop.
Therefore, the longer the length and the wider the width of the faulted area, the larger the resulting magnitude. The topmost, brittle part of the Earth's crust, the cool slabs of the tectonic plates that are descending down into the hot mantle, are the only parts of our planet which can store elastic energy and release it in fault ruptures. Rocks hotter than about 300 °C flow in response to stress; the maximum observed lengths of ruptures and mapped faults are 1,000 km. Examples are the earthquakes in Chile, 1960; the longest earthquake ruptures on strike-slip faults, like the San Andreas Fault, the North Anatolian Fault in Turkey and the Denali Fault in Alaska, are about half to one third as long as the lengths along subducting plate margins, those along normal faults are shorter. The most important parameter controlling the maximum earthquake magnitude on a fault is however not the maximum available length, but the available width because the latter varies by a factor of 20. Along converging plate margins, the dip angle of the rupture plane is shallow about 10 de
An extensional fault is a fault caused by stretching of the Earth's crust. Stretching horizontally extends portions of the crust and/or lithosphere. In most cases such a fault is a normal fault, but may create a shallower dip associated with a thrust fault. Extensional faults are planar. If the stress field is oriented with the maximum stress perpendicular to the Earth's surface, extensional faults will create an initial dip of the associated beds of about 60° from the horizontal; the faults will extend down to the base of the seismogenic layer. As crustal stretching continues, the faults will rotate, resulting in steeply-dipping fault blocks between them. Extensional tectonics Graben
Long Point–Eureka Heights fault system
The Long Point–Eureka Heights fault system is a system of geologic faults in Houston, Texas. It runs beneath the metropolitan area from the southwest to the northeast; the various faults are characterized as normal faults, meaning that the downthrown side is in the direction of the dip of the fault plane. This fault system as well as others located in nearby parts of Texas are believed to have formed millions of years ago during the formation of the Gulf of Mexico. No significant earthquakes have occurred on these faults in historic times, but slow movement has been observed. Houston: On Shaky Ground University of Houston fault map Fault Map