The Hayward Fault Zone is a geologic fault zone capable of generating significantly destructive earthquakes. About 60 kilometers long, it lies mainly along the western base of the hills on the east side of San Francisco Bay. It runs through densely-populated areas, including the cities of Richmond, El Cerrito, Berkeley, Oakland, San Leandro, Hayward, Fremont, and San Jose.
The Hayward Fault is parallel to its more famous (and much longer) westerly neighbor, the San Andreas Fault, which lies offshore and through the San Francisco peninsula. To the east of the Hayward lies the Calaveras Fault. The Hayward Fault merges with these two fault systems south of San Francisco Bay.
North of San Pablo Bay, and somewhat offset from the Hayward Fault is the Rodgers Creek Fault, considered by many to be an extension of the Hayward Fault Zone. Another fault further north, the Maacama Fault, is also 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 Fault takes up a share of the overall motion between the plates.
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 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, but relatively southeast along the faultline. 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.
As the transform boundary defined by the San Andreas Fault is not perfectly straight, and the motion of the North American plate is not entirely parallel to the plate boundary, movement along the boundary creates stresses in the crust on either side of the boundary, resulting in additional faulting on both sides of the San Andreas Fault. The Hayward Fault is one of the larger faults created this way, along with the Calaveras Fault and the San Gregorio Fault.
In fact, the 1868 quake became known as the "Great San Francisco Earthquake" until the larger tremor in 1906.The last truly major earthquake in the region was the 1906 San Francisco Earthquake which occurred on the San Andreas fault. Many seismologists believe that the 1906 earthquake reduced the stress on many faults in the Bay Area including the Hayward fault, creating an "earthquake shadow": a quiescent period following a major earthquake. Since the 1906 San Andreas event there have been no moderately strong earthquakes on the Hayward fault as were seen before that earthquake. It also appears likely that this quiet period in the earthquake shadow is ending, as projected by the rate of plate motion and the stress state of other faults in the region.
The following table chronologically lists all of the historic earthquakes on the Hayward Fault Zone which have exceeded magnitude 5.5.
| Year | City | Date | Magnitude | Epicenter and notes |
|---|---|---|---|---|
| 1864 | South Hayward area | May 21, 1864 | 5.8 | Epicenter coordinates:-121.9, 37.6 |
| 1868 | Hayward | October 21, 1868 | 6.8 to 7.0 | Epicenter coordinates: longitude -122.10, latitude 37.70. This event left 30 dead, and $350,000 in property damage. |
| 1870 | Berkeley | April 2, 1870 | 5.8 | Epicenter coordinates:-122.3, 37.9 |
| 1889 | Alameda County (now east Oakland area) | July 31, 1889 | 5.6 | Epicenter coordinates:-122.2, 37.8 |
The 1868 earthquake occurred well before the East Bay region was extensively urbanized. The following year, in 1869, the William Meek Estate became one of the first developments in the area, built on 3,000 acres (12 km²) in what became known as the Cherryland district of Eden Township. Recent renovations of the Meek Mansion have revealed that with the 1868 earthquake still fresh in minds of residents of the time, some unusual diagonal bracing was built into the original construction. Although its magnitude was less than the 1906 San Francisco Earthquake, the intensity of shaking experienced in the Hayward area may have been greater than in 1906 due to the proximity of the Hayward Fault.
During 2007, a number of small earthquakes occurred on the northern segment of the Hayward Fault from Oakland to Berkeley.
On Oct 30th 2007 at around 8 PM local time, a magnitude 5.6 struck the adjacent Calaveras Fault near San Jose, close to where the Hayward Fault diverges from it. The effects of an earthquake of this size include the spilling of merchandise from store shelves but little structural damage. An earthquake of this size can be locally terrifying, however, and this particular event was also widely felt through Northern California (as far north as Oregon) owing to the time of day, when most people were awake and sitting quietly in their homes. Minor aftershocks have continued through Spring 2008.
Of all the region's large faults, the Hayward-Rodgers Creek fault system is considered most likely to create the next major destructive earthquake in the near future. Less-destructive earthquakes have been occurring in the region at random 15 to 30 year intervals - typically causing spillage of merchandise and occasionally, structural failures in lower stories and chimneys. This type of event is considered normal in California's "Earthquake Country" by geologists and long term natives, although disquieting to recent immigrants to the region. A major event on either the Hayward or San Andreas could produce a minute or more of intense shaking, as was felt in the Kobe earthquake. The ground conditions in that region of Japan are quite similar to those in the East Bay and that earthquake destroyed what were considered to be modern and well engineered structures. This was seen especially in the failure of elevated urban road structures and buildings due to soil failure.
The estimated probability of a major earthquake on the Hayward within the next thirty years was estimated at nearly 30 percent, compared to about 20 percent for the San Andreas Fault, which can have larger earthquakes but further away from a significant portion of the urbanized parts of the Bay Area. Recent (January 2008) assesments suggest that the Hayward, Rodgers Creek, and Calaveras faults may be more likely to fail in the next few decades than previously thought.
The 140th anniversary of the 1868 event is in 2008, and the average time between the last five major events is also averaged at 140 years. Recent estimates of the damage potential of a major Hayward Fault earthquake by a professional risk management firm indicate the potential for huge economic losses, of which only a small percentage is insured against earth movement. (Earthquake insurance is not only quite expensive, it tends to be burdened with huge deductibles - at least 15 percent). Depending upon seasonal weather conditions at the time of a major event a seismic event could be followed by huge urban wildfires compounded by damage to water systems or massive landslides in saturated soils. In addition to direct damage the effects on commerce due to damaged infrastructure would also be substantial. Experience with large area urban destruction such as caused by earthquake, hurricane, and firestorms has shown that complete rebuilding can take up to a decade, owing to various factors including disputes with insurance companies, a lack of qualified local builders, shortages of supplies, an influx of contractors from outside of the region of dubious qualifications and with no incentive to maintain and enhance a local reputation.
The progressively more severe reports and estimates of event probability and consequences have awakened a broad interest in training people for emergency response. It is becoming widely understood that professional fire fighting, police, and medical services will be overwhelmed by a major event and that neighbors will have to assist each other as best they can. As of Spring, 2008 there has been little government interest in fostering support for organizations akin to the Civil Defense (CD) efforts of the late 1940s and early 1950s.
The complete fault zone, including the Rodgers Creek fault, is divided by seismologists into three segments - Rodgers Creek, Northern Hayward, and 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 (ABAG) 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 likely possible combinations.
While there are indications that a substantial earthquake on a nearby parallel fault can release stress and so also the near–term probability of an earthquake, the opposite appears to be true concerning sequential segments. A release on a major segment can substantially 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.
Shaking intensity maps for various Hayward and Rodgers Creek Fault earthquake scenarios, from ABAG Quake website
Further improvement in the construction of resistant structures and the development of retrofitting method have only recently been developed, largely in response to the effects of the 1971 Sylmar, 1989 Loma Prieta, and 1994 Northridge events in California – none of which were hugely catastrophic, but each of which caused loss of life in structures not thought to be vulnerable, and so increased public, engineering, and government awareness of the need for specific remediations and construction methods required for improved life safety.
Although many structures have undergone seismic retrofitting there are a large number of dangerous un-reinforced masonry (mostly brick) structures and chimneys, which can be extremely hazardous to occupants in a large earthquake, and a large number of buildings which are either not bolted to their foundations or which are elevated upon partial stories that are insufficiently resistant to shear forces. Foundation and partial story weaknesses are easily remediated in most cases, but this is only effective if the work is competently done, with proper attention to minor details such as nailing patterns and proper connections. Local surveys of recently completed work have exposed deficient workmanship in a number of cases involving household retrofits. For the recommendations of a public agency for simple low-rise construction see this City of San Leandro site
Warren Freeway portion of Highway 13
In its northern extent, the Hayward Fault lies directly beneath the portion of Highway 13 (the Warren Freeway) that is south of its intersection Highway 24 and north of its terminal connection with Interstate 580 (the MacArthur Freeway). In this rift valley there are a number of elevated street crossings in the Montclair District that cross the fault.
Highway 24
State Highway 24, connecting Oakland to Orinda, Lafayette, and Walnut Creek through the Caldecott Tunnel, is composed of extensive earth fill at the location where the fault is crossed. An earthquake may cause minor landsliding on some slopes of the freeway, and the plastic movement of the fill would likely disrupt the pavement if the movement here of the surface displacement is substantial, possibly presenting a hazard to motorists and shutting down the highway for a while. More extensive disruption and greater hazard could be caused by the failure of elevated structures, both those over which the highway passes and overcrossings of the freeway, of which there are two nearby. As elsewhere in the area, such structures have undergone extensive retrofitting for safety.
Highways 80 and 880 and the Port of Oakland
A severe earthquake is more likely to disable the offshore causeway portions of Interstate Highway 80 (the Eastshore Freeway), since it is built on fill placed in the 1930s atop mudflats whose upper layers were deposited in the 19th century as a result of extensive hydraulic gold mining in the distant Sierra Nevada mountain foothills. This soft mud is expected to amplify earthquake shaking, and the mud supporting the heavy fill may liquefy, and so possibly cause major disruption of the highway due to failure by sinking of the highway and by differential movement of large sections. (More modern construction for these conditions employs linked and "floating" - in mud - lightweight concrete and plastic foam box structures to support a road.) Similar conditions underly the eastern approach roads the Bay Bridge. Better, but still locally poor soils underlie the portion of Interstate Highway 880 that extends to the South Bay region from the eastern terminus of the San Francisco – Oakland Bay Bridge. As the bulk of cargo containers from the Port of Oakland travel on these two roads, the disabling of both would cause severe disruption of west coast import and export goods, owing to the consequent overloading of other West Coast container handling ports. Such disruption would be minor compared to that which could be produced by a large southern California earthquake, as the bulk of west coast container traffic is through the ports of Long Beach and Los Angeles.
Highway 580
A major route for commuters travelling from Southern Alameda County and the East Bay hills to downtown Oakland and San Francisco, Interstate 580 crosses the fault twice, and runs very close to the fault between the intersections with State Route 13 (the Warren Freeway) and Interstate 238.
The 1989 Loma Prieta earthquake caused a failure of a single section of the upper deck of the eastern span of the San Francisco – Oakland Bay Bridge, which closed the bridge for 30 days. Engineers and much of the public have long recognized that a strong earthquake centered closer to the bridge on either the Hayward or San Andreas faults could cause a complete collapse of the eastern span. A replacement eastern span is currently under construction, with completion projected for late 2013 (originally 2010).
Transbay tube
BART trains travel between San Francisco and Oakland through a tube structure. The tube is composed of welded plate steel segments. Each oval outer section carries two inner train tubes of circular cross section and a central rectangular access and rescue tunnel, with the void between elements filled with concrete. The segments were sunk into a ditch dredged through bay mud and covered with rock fill, and then pumped free of water upon completion, making the resulting tube somewhat buoyant, but held in place with a rock overfill. Subsequent seismic analysis indicated the possibility that the overfill could fail due to agitation, allowing the buoyant tube to float upward, misaligning the tracks and possibly over stressing the bolted connections. This potential problem has been addressed by vibratory compaction of the overfill covering the tube. Additional stabilization will include the driving of large pilings and the connection of additional restraints.
Slip joint
The transbay tube terminates at an under-bay slip joint near the Embarcadero Station in San Francisco. The designed slip margin has been reduced by half due to unforeseen settlement of the tube structure. The projected worst-case motion at this joint has been determined to be beyond that for which the joint is presently capable, which could cause severe structural problems and mud and water entry into the tube and adjacent subway systems. This is to be corrected at great expense – first estimated at $142 million but expected to cost far more – probably the largest single cost item in the list of BART seismic retrofits.
Berkeley Hills Tunnel
In June 2006 Bay Area Rapid Transit (BART) management announced that they have elected not to modify the Berkeley Hills Tunnel, which actually penetrates the Hayward Fault, arguing that it would be cheaper (and less disruptive to current operations) to rebore a misaligned portion after the fact than to protect riders (either by extensive modifications of the tunnel or by replacing it with a higher bore) against the small likelihood that a train (or two) would crash into or be cut in two by a major slippage of the fault. Modified train scheduling to prevent multiple train exposure at faults has been determined by BART engineers to be impractical due to variations in train passage, but automated event-related realtime train operational response is considered practical (see below).
Seismic sensor network
BART has installed and continues to enhance a network of seismic sensors (an earthquake warning system) to trigger a system halt in the event of a major event, this to include automated event progression analysis to determine the best action with regard to individual trains for maximum safety (a fault rip can take up to several tens of seconds to completely propagate from the epicenter to the affected locations). Such sensor networks and warning devices have a potential to reduce the hazards from falling objects and furnishings provided that the people notified are well trained in appropriate responses (similar to the Cold War's "duck and cover" training of schoolchildren).
Of primary concern with respect to the Hayward Fault is the huge Chevron oil refinery in Richmond. Although founded on better ground than most of the shoreline, this refinery has extensive crude oil and finished product docks and pipelines extending into the bay, which could produce catastrophic spills into the bay, with the potential to adversely affect hundreds of miles of sensitive wetlands. Dismantling of high pressure and temperature process units and the consequent fire danger to personnel and equipment could produce substantial economic consequences for the western states. Large liquid storage tanks are protected by berms that are designed to contain the contents should a tank fail under normal conditions. Similar process and product conditions exist at other refineries further inland near Martinez, but mostly these plants are exposed to earthquakes from other faults.
The Hetch Hetchy Aqueduct, which supplies 270 to 315 million gallons of water per day to the City of San Francisco and other Bay Area communities, directly crosses the Hayward Fault in Fremont. A 2002 report by the Bay Area Economic Forum suggests that a breakdown in the aqueduct due to an earthquake could cut off Hetch Hetchy water to the Bay Area for 60 days. In addition to depriving 85% of San Francisco residents of their drinking water, this would cut off supplies for firefighting and water-intensive industry, causing economic damage of $17.2 to $28.7 billion dollars.
Many of the structures at UCB academic campus have been self rated as having "poor" earthquake performance. Numerous chemical, radiological, and biohazardous materials are present (in relatively small quantities) on campus and on the associated Lawrence Berkeley National Laboratory, in the hills above the university.
Memorial Stadium
Further north the fault passes under the lengthwise midline of the football field of California Memorial Stadium at the University of California, Berkeley. Fault creep since 1923 has offset the walls at the north and south ends 13 inches (33 cm). There are no plans at this time to replace the stadium in its entirety at a more appropriate location, even though its "O" shape may possibly be split into two "C"s. A suitable site for a replacement is available immediately to the east in Wildcat Canyon, although this would require an east-west alignment rather than the traditional north-south orientation. While there is only a small probability of an earthquake on this fault while the stadium is occupied, the results could be deadly.
Seismic improvements are planned to coincide with extensive renovations to the football players' facilities, spurred by the recent retention of a popular coach as part of his contract negotiations. The detailed nature of the seismic renovations has not yet been made public, but a detailed walk-through of the stadium offers some clues as to possible solutions, found here (PDF document), probably involving rebuilding portions of the stadium upon floating mats (foundations that do not penetrate the surface, rather sitting upon level graded gravel) where they pass over and near the fault, with appropriate sliding connections for the safety of spectators.
Cellphone and most landline telephone service, while theoretically survivable for a short time on battery and emergency power could instead suffer immediate disruption from ground shaking effects.
Similar dangerous soil conditions and insufficiently resistant buildings are also on the southern, western and northern boundaries of San Francisco and San Pablo bays and would also be severely affected by a major earthquake on the Hayward fault. As that portion includes the so-called Silicon Valley, the potential economic disruption due to destruction of works in progress and the dismantling of microelectronics fabrication plants could have an economic effect extending worldwide. The current estimates of the probability of a major earthquake on any of the numerous regional faults range up to 70 percent within the thirty year period 2000-2029. A recent quiet period following many years of minor activity is considered to be particularly ominous by many, although geologists have not yet been able to predict earthquakes with any useful accuracy. They do warn that all residents of the region should be prepared for a large event and its subsequent effects (e. g., lack of water, firefighting, first aid, electricity, motor and heating fuels, etc.) and that much life-safety protective work remains to be done.
It is primarily the likelihood of a severe earthquake on the Hayward or San Andreas faults that has spurred a substantial effort to retrofit and sometimes replace large structures at risk, particularly the eastern and western spans of the San Francisco – Oakland Bay Bridge, the San Francisco and Oakland city halls, and numerous elevated rail, road, and pedestrian structures and overpasses. Much work remains to be done in the region and progress is being hampered by budget constraints imposed by trickle down federal-state-regional deficits, design and construction delays due to state and local political bickering over design, and unexpectedly high steel and cement costs due to the extensive construction work being done in China.
The Google Earth website, in cooperation with the United States Geological Survey has prepared a virtual helicopter tour of the fault, with much additional information available through the tour. Potentially dangerous landslide areas are also marked, showing great areas beyond the fault that could be rendered uninhabitable by a major event.
The James Bond movie A View to a Kill (1985) involved a plot, referred as "Main Strike", by Max Zorin to detonate explosives along the Hayward Fault, San Andreas Fault and at the "geological lock" to flood the two faults with water from nearby lakes and cause both faults to move causing a "double earthquake" that would destroy Silicon Valley, all in order for Zorin to monopolize the microchip market.
This geotourism exhibit (April through October 2006, now closed) featured a 12- to deep pit exposing the Hayward Fault, which could be viewed "face to face" from a shaded platform by descending a staircase. Significant features were noted and marked. Similar trench excavations are used in the determination of the frequency and magnitude of prehistoric earthquakes and to determine the location of latent faults as part of the science of Paleoseismology
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