Hayward Fault
The Hayward Fault Zone is a geological transform fault with the potential for earthquakes of significant magnitude and destruction. The fault is approximately 119 km long and lies primarily along the western base of the hills on the east side of the San Francisco Bay . It passes through densely populated areas starting near Richmond in the north, continuing south via El Cerrito , Berkeley , Oakland , San Leandro , Hayward , Union City , Fremont and to San Jose .
To the west parallel to it lies the famous (and much longer) neighbor, the San Andreas Fault , which, however, is partly in the sea off the coast and runs through the San Francisco Peninsula. To the south of the Hayward Fault Zone is the Calaveras Fault . In 2007 it was discovered that the Hayward Fault east of San Jose merges into the Calaveras Fault at a depth of 6.4 km and has the potential to generate significantly stronger earthquakes than previously thought. Some geologists suggested that the southern Calaveras Fault be renamed the Southern Hayward Fault.
North of San Pablo Bay is the Rodgers Creek Fault , which is believed to be an extension of the Hayward Fault. The Maacama Transform Fault a little further north is also considered to be part and subsystem of the Hayward Fault Zone.
While the San Andreas Fault is the main transform fault boundary between the Pacific and North American plates , the Hayward fault also accounts for some of the total movement between the plates.
tectonics
The Pacific plate is an important part of the Earth's crust , which is gradually expanding and enlarging as magma erupts to the southeast along the East Pacific Ridge . In the northwest, it pushes under the North American Plate and forms the Aleutian Trench in the subduction zone there . In California , the plate is sliding northwest along the San Andreas Fault transformation boundary. At the same time, the North American Plate is moving in a south-westerly direction, but in a south-easterly direction relative to the fault. The movement of the western part of the North American Plate creates a certain force along the San Andreas Fault and the associated faults and thus helps to lift the mountain ranges on the North American Pacific coast and other parallel inland mountain ranges west of the California Long Valley, in this region this is especially the Diablo Mountains . The Hayward Fault shows the same relative motions as the San Andreas Fault. As with other faults, much of the Hayward Fault's impact is formed by a narrow complex zone of deformation that can extend up to several hundred meters in width.
The San Andreas Fault transformation boundary is not entirely straight, and the tensions between the Pacific and North American plates are spread over much of the west and extend to the east side of the Sierra Nevada . The Hayward Fault, along with the Calaveras Fault to the east and the San Gregorio Fault to the west of the San Andreas Fault, is one of the secondary faults in this diffuse zone.
The entire fault zone, including the Rodgers Creek Fault, is divided into three segments by seismologists - Rodgers Creek , North Hayward, and South Hayward . These segments, individually or in adjacent pairs, are expected to generate earthquakes of varying magnitude. The Association of Bay Area Governments ( Association of Bay Area Governments , ABAG ) has promoted cooperation with other government agencies to analyze the local conditions and the creation of maps that are to demonstrate the destructive potential of these earthquakes.
While there are indications that a strong earthquake in a nearby, parallel fault can relieve stresses and thus also reduce the short-term probability of an earthquake, the opposite appears to be the case for neighboring segments. Relieving stress in a large segment can essentially increase the likelihood of an earthquake in a neighboring fault, and thus also increase the likelihood of two large regional earthquakes within a few months.
Rodgers Creek Fault
The link between the Rodgers Creek Fault and the Hayward Fault was unclear until 2015 when an underground survey of San Pablo Bay revealed that the ends of the two faults are seamlessly connected between Point Pinole and Lower Tubbs Island . An earlier, alternate hypothesis suggested that the Hayward Fault and Rodgers Creek Faults are likely connected by a series of staggered fault lines under San Pablo Bay. The new findings meant that the Rodgers-Hayward system could collectively create an earthquake as strong as 7.2. It is also believed possible that a major seismic event in one of the faults could also cause movement in the other fault, either simultaneously or within an interval of up to several months. The Association of Bay Area Governments created maps depicting a possible simultaneous scenario (see below).
Calaveras Fault
The Calaveras fault is believed to extend continuously from the Sunol area to south of Hollister . For a long time it was assumed that there was no connection between the Hayward and Calaveras faults. However, recent geological studies (particularly testing of very small and deep earthquakes) suggest that the two faults may be linked. If so, it would have a significant impact on the potential maximum magnitude of earthquakes in the Hayward Fault, as this force is determined by the maximum length of the fault line of the fault, and that fracture extends beyond the junction and thus forms part of the Calaveras Fault. Could include disorder. (This potential is not shown in the earthquake strength maps shown below.)
earthquake
The largest Hayward Fault quake on record occurred in 1868 , with an estimated magnitude of 7.0. It occurred in the southern portion of the fault and got its name (a few decades later) from the nascent town of Hayward , where the epicenter of the quake was believed to be. However, the 1868 quake caused great damage to the entire then sparsely populated Bay Area, including the city of San Francisco. In fact, from 1868 until the major earthquake in 1906, the event became known as the "Great San Francisco earthquake".
Many seismologists believe that the 1906 San Francisco earthquake that occurred in the San Andreas Fault reduced the tension in the Bay Area in many faults, including the Hayward Fault, and created an "earthquake shadow" : a dormant period after a major earthquake. Since the 1906 event in the San Andreas Fault, there have been no other moderately strong earthquakes in the Hayward Fault as seen prior to that earthquake. It seems likely that this quiet period will end in the earthquake shadow, as indicated by the speed of the plate movement and the state of stress from other faults in the region.
The following table chronologically lists all historical earthquakes in the Hayward fault zone with a magnitude greater than 5.5.
| year | city | date | Magnitude (M L ) | epicenter | Remarks |
|---|---|---|---|---|---|
| 1864 | South Hayward Area | May 21, 1864 | 5.8 | 37 ° 36 ′ 0 ″ N , 121 ° 54 ′ 0 ″ W. | |
| 1868 | Hayward | October 21, 1868 | 6.8 to 7.0 | 37 ° 42 ′ 0 ″ N , 122 ° 6 ′ 0 ″ W. | 30 dead and $ 350,000 property damage |
| 1870 | Berkeley | April 2, 1870 | 5.8 | 37 ° 54 ′ 0 ″ N , 122 ° 18 ′ 0 ″ W. | |
| 1889 | Alameda County (now East Oakland Area ) | July 31, 1889 | 5.6 | 37 ° 48 ′ 0 ″ N , 122 ° 12 ′ 0 ″ W. |
The earthquake of 1868 occurred some time before the eastern region of the San Francisco Bay Area was extensively urbanized. The following year, 1869, the William Meek Estate was one of the first developments in this area to be built on 12 km² of land and known as the Cherryland District of Eden Township . Recent renovations to the Meek Mansion have shown that, with the earthquake of 1868 fresh in the minds of residents of that time, some unusual diagonal bracing was incorporated into the original structure. Although its strength was smaller than the 1906 earthquake in San Francisco, the intensity experienced in the Hayward region is likely to have been greater than in 1906, due to the proximity of the Hayward Fault.
Earlier earthquakes were detected by trench exposure and associated radiocarbon dating. Combined with the historical records, it turns out that the last five major events occurred in the years 1315, 1470, 1630, 1725 and 1868 with intervals of about 140 years.
Probability of future events
Scientists from the United States Geological Survey (USGS) claim that a major earthquake is "becoming increasingly likely" in the zone. When the next major earthquake hits the fault, the damage will be catastrophic. In the region there are properties worth more than 1.5 trillion US dollars and the earthquake of 1868 would occur again, a loss of more than 165 billion dollars would be likely. Since the fault runs through densely populated areas, more than 5 million people would be directly affected and 2.4 million people living in California's San Francisco Bay Area could be cut off from water.
The probability of a major earthquake in the Hayward Fault within the next 30 years has been estimated at almost 30%. In comparison, the probability of the San Andreas Fault is around 20%, although larger earthquakes can occur there, but they are further away from a substantial portion of the Bay Area's urbanized regions. Recent (January 2008) assessments suggest that the likelihood of earthquakes in the Hayward, Rodgers Creek and Calaveras faults over the next few decades is greater than previously thought.
The 140th anniversary of the 1868 event was in 2008 and the average time between the last five major events is also 140 years. Recent estimates by a professional risk management firm of the potential for a major Hayward Fault earthquake show the potential for enormous economic losses, only a small percentage of which are earthquake insured. (Insurance against earthquakes is generally not only very expensive, but also often has high deductibles - usually at least 15%). Depending on the seasonal weather conditions at the time of a major seismic event, major urban forest fires due to damage to water systems or massive landslides could result. In addition to the direct damage, the impact on trade from damaged infrastructure would be significant. Experience with destruction in large urban areas from earthquakes, hurricanes and conflagrations has shown that complete reconstruction can take up to a decade. The reasons for this include disputes with insurance companies, a lack of qualified local builders, the shortage of supply, and the influx of contractors from outside the region with dubious qualifications and no incentive to maintain or improve the reputation.
The increasingly strict reports and assessments of the probability of occurrence and the consequences have sparked a broad interest in training people for emergency response. It is becoming more and more popular that, in the event of a major event, professional fire-fighters as well as the police and medical services will be overwhelmed and that neighbors have to support each other as best they can. Corresponding organizations would likely be similar to the civil defense structures in the 1950s, but such civilian participation would have to be organized.
In 2012, USGS scientists said that an earthquake on the order of 6.8 to 7.0 was expected in the fault. The California Geological Survey also agreed, saying the probability of a magnitude 6.7 earthquake or greater along the Rogers-Creek-Hayward Fault is 31% over the next 30 years.
In March 2015, the United States Geological Survey published UCERF3: A New Earthquake Prediction for Complex Fault Systems in California. UCERF3 represents the best currently available scientific knowledge and, in addition to historical seismicity, it now also includes “multifault ruptures” and “fault readiness” in the earthquake forecast. According to experts, the result for residents of the San Francisco Bay Area states that there is a 72% chance of experiencing an earthquake of magnitude 6.7 or greater in the next 30 years. In addition, there is a 51% chance of an M≥7 earthquake (threshold for “large” earthquakes), a 20% chance for M≥7.5 and a 4% chance for M≥8 (an “extraordinary “Quake) when all known faults in the region are taken into account.
Effects of the fault
Fault creep
The surface of the disorder creeps in the relevant regions with less than 0.5 cm per year. The southernmost regions of the fault creep faster, possibly sufficient to prevent the fault from breaking there, but the creep is usually insufficient to reduce the forces occurring in most of the fault and thus does not prevent a large earthquake. The creep is strong enough to move streets, curbs and sidewalks so that the surface trail is visible in many places. Creep damage on asphalt road surfaces usually occurs as a series of staggered cracks. Creep effects can also be seen in older structures built immediately above the fault, some of which have been fitted with expansion joints to compensate for the slow movement.
Earthquake tremors
The strength of an earthquake, as measured in the moment magnitude scale (or for smaller events in the better known Richter scale ), is roughly proportional to the length of the fracture. Soil motion in a large region surrounding the fault is dependent in large part on local soil conditions and to a lesser extent on the distance and ratio of progression of the fault's fracture and (as recently recognized in the 1989 Loma Prieta earthquake ) on reflected energy from deep imperfections in the structure of the earth. The area affected by an earthquake also depends on the density and evenness of the soil surrounding the fault.
Potential combined earthquake on Rodgers Creek and North Hayward Faults. Magnitude 7.1
Potential earthquake tremor on the North Hayward Fault. Magnitude 6.5
Potential earthquake tremor on the South Hayward Fault. Magnitude 6.7
Final reviews of damage reports from the 1868 event indicate that the fracture of even parts of the north and south Hayward Faults could produce a 7.0 magnitude quake. This is significantly stronger than the event of magnitude 6.5 shown here or the previously assumed maximum magnitude of 6.7.
The terms used by the ABAG ( Association of Bay Area Governments ) for the intensity of the tremors differ from the official descriptions of the Mercalli scale, being somewhat softened (perhaps due to extensive experience on site with earthquakes), using terms such as " Rather Strong "becomes" Light "and" Ruinous ", and" Disastrous "becomes variations of" Violent ".
Bay-side ground conditions
The Hayward Fault is considered particularly dangerous due to poor soil conditions in the alluvial plain that slopes from the East Bay Hills to the east coast of San Francisco Bay . In the lower elevations near the bay, the bottom is mostly water-saturated mud and sand that was deposited in the marshland there in the early 20th century . This soil tends to amplify the effects of earthquakes, creating much greater ground movement. In addition, the ground itself can fail and, due to the movement, turn into a liquid sludge, which is not able to support buildings on previously solid ground. This region was also densely populated with low-rise buildings, most of which were built shortly after the 1906 San Francisco earthquake , long before even moderately earthquake-proof construction practices were developed in the late 1920s.
Further improvements in the design of resilient buildings and methods of retrofitting have only recently emerged, largely in response to the effects of the events in Sylmar in California in 1971 , in Loma Prieta in 1989, and in Northridge in 1994 . None of them have been extremely catastrophic, but each has caused loss of life in buildings that are not classified as endangered, thus increasing public, engineering and government awareness of the need for specific life-safety-enhancing renovations and construction methods .
Although many buildings have undergone seismic retrofitting, there are a large number of unreinforced, masonry buildings and chimneys (mostly bricks) that can be very dangerous for residents in a major earthquake, as well as a large number of buildings that use their foundations either are not screwed or which are built on a mezzanine that is not sufficiently resistant to shear forces. Weaknesses in the foundation and mezzanine can be easily repaired in most cases, but this is only effective if the work is done competently and with the right attention to small details such as nail patterns and the right connections. Local surveys of recently completed work have shown poor workmanship in a number of cases where households have been upgraded.
landslide
There is plenty of small active and evidence of numerous large previous landslides in the Berkeley Hills. Such areas are believed to be stable only under current conditions. There is a possibility that a large earthquake could cause very large earth movements, especially if the soils are seasonally saturated with water and so potentially large areas become uncultivated.
Additional information
Virtual tour
Google Earth , in collaboration with the United States Geological Survey, prepared a virtual helicopter tour of the fault, enriched with a lot of additional information during the tour. There are also potentially dangerous landslide areas marked to show the large areas outside the fault zone that could become uninhabitable in a major event.
Trivia
The novel A Man in Full by Tom Wolfe is characterized by a fictional major earthquake triggered in the Hayward Fault. This is used as a deus ex machina method and as an important point in the development of the plot (to free a main character from prison).
The James Bond film Facing Death (1985) is about Max Zorin who wants to detonate explosives along the Hayward Fault as well as the San Andreas Fault and an underground geological weak point to use water from nearby lakes. double earthquake "which would destroy Silicon Valley and Zorin would further expand his monopoly on the microchip market.
Special exhibition
Fremont Earthquake Exhibit: The Hayward Fault Exposed
This geotourism exhibition (from April to October 2006, now closed) featured an approximately 5 m deep pit where you could see the Hayward Fault "face to face" from a shady platform that was accessible by stairs. Essential features have been identified and marked. Similar exposures are normally used to determine the frequency and strength of prehistoric earthquakes and to assess the location of latent faults in the course of paleoseismology .
- Extensive additional material providing information on the geology and seismology of the Bay Area has been prepared for the exhibit, most of which is currently available online.
- The funding and organization for a permanent exhibition at this location is actively sought, the planning is in progress.
Web links
Individual evidence
- ^ Hayward Fault Fact Sheet. In: www.conservation.ca.gov. October 7, 2008, accessed July 8, 2016 .
- ↑ a b Major quake on Hayward fault more likely, scientists say. December 11, 2007, accessed July 8, 2016 .
- ↑ Mort Larsen, Carol S. Prentice, Harvey M. Kelsey, Judith Zachariasen, Gabriel L. Rotberg: Paleoseismic investigation of the Maacama fault at the Haehl Creek site, Willits, California . In: Geological Society of America (Ed.): Abstracts with Programs . tape 37 , no. 4 , 2005, p. 68 (English, gsa.confex.com ).
- ↑ United States Bureau of Reclamation (Ed.): North of the Delta Offstream Storage Investigation (Draft) . S. 26 ( water.ca.gov [PDF; accessed July 8, 2016]).
- ↑ 1864 May 21, 2:01 GMT. (No longer available online.) July 19, 2007, archived from the original on July 19, 2007 ; Retrieved July 9, 2016 .
- ^ California Geological Survey - Regional Geologic Mapping Program. (No longer available online.) In: www.conservation.ca.gov. Archived from the original on July 9, 2016 ; accessed on July 9, 2016 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ 1868 October 21, 15: 53GMT. (No longer available online.) September 26, 2006, archived from the original on September 26, 2006 ; Retrieved July 9, 2016 .
- ↑ 1870 April 2, 19: 48GMT. (No longer available online.) September 26, 2006, archived from the original on September 26, 2006 ; Retrieved July 9, 2016 .
- ↑ 1889 July 31. (No longer available online.) September 26, 2006, archived from the original on September 26, 2006 ; Retrieved July 9, 2016 .
- ↑ Julie Sevrens Lyons: Study: 1868 temblor larger than earlier thought . In: The Daily Review (Hayward) . Bay Area News Group, Hayward, CA, USA February 6, 2007, p. 1 (English).
- ^ Fremont Earthquake Exhibit. (No longer available online.) Msnucleus.org, archived from the original on August 12, 2006 ; Retrieved July 8, 2016 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ Math Science Nucleus (Ed.): Toward a Permanent Trench and Earthquake Walk on the Hayward Fault, in Central Park, Fremont . ( msnucleus.org [PDF; accessed July 8, 2016]).
