Hayward Fault Zone

[1] This fault is about 119 km (74 mi) long,[2] situated mainly along the western base of the hills on the east side of San Francisco Bay.

The transform boundary defined by the San Andreas Fault is not perfectly straight, and the stresses between the Pacific and North American plates are diffused over a wide region of the West, extending as far as the Walker Lane east of the Sierra Nevada.

The Association of Bay Area Governments has prepared ground shaking maps that include a possible concurrent scenario (these are shown below).

A simultaneous rupture of the connected Hayward-Rodgers Creek Fault – about 118 mi (190 km) 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 occurred on the southern segment of the fault, receiving its name (some decades later) from the nascent town of Hayward where it was determined the quake's epicenter was located.

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.

[15] 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.

[19] This is compared to 6.4 percent for the San Andreas Fault, which can have larger earthquakes but is farther away from a significant portion of the urbanized parts of the Bay Area.

[19] Earlier (January 2008) assessments suggest that the Hayward, Rodgers Creek, and Calaveras faults may be more likely to fail in the next few decades than previously thought.

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.

The progressively more severe reports and estimates of event probability and consequences have awakened a broad interest in training people for emergency response.

The UCERF3 represents the best available science to date, and it now considers "multifault ruptures" and "fault readiness", in addition to historical seismicity, in the calculus of earthquake forecasting.

The magnitude of an earthquake, as indicated on a seismic scale, is roughly proportional to the length of the rupture, while the ground motion in the region surrounding the fault is highly dependent upon the local soil conditions, somewhat upon the distance and relationship to the progression of the fault rupture, and (as recently recognized in the 1989 Loma Prieta earthquake) reflected energy from deep discontinuities in the Earth's structure.

At the lower elevations near the bay the soil is mostly water saturated mud and sand, placed in the early 20th century as fill in marsh areas.

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.

Severe effects were seen in both Oakland and northern San Francisco from the 1989 Loma Prieta earthquake, even though this event was not extremely large and was centered a significant distance away in the Santa Cruz Mountains.

(More modern construction for these conditions employs linked and "floating" – in mud – lightweight concrete and plastic foam box structures to support a road.)

Engineers and much of the public had long recognized that a strong earthquake centered close to the bridge on either the Hayward or San Andreas faults could cause a complete collapse of the eastern span.

Derailments have often occurred during major earthquakes, both directly by tipping and by roadbed failures; industrial accidents involving these materials have caused extensive health hazards in the mixed residential–industrial areas of Richmond.

In addition to extensive modifications to over crossings and elevated structures, largely to prevent dismantling due to shaking or destruction by soil failure, several other unique system feature require special treatment.

Additionally, EBMUD created a second route to bring water to these west-of-the-hills customers through the Southern Loop Bypass near Castro Valley.

[26][27] 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.

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 $17.2–28.7 billion.

The fault continues north under the eastern margin of Lake Temescal and its dam, which is unlikely to fail since it has been completely reinforced by the extensive earth fill supporting the subsequently improved Highway 24.

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.

The work was the subject of several lawsuits from neighborhood and environmental groups, who were concerned about such extensive construction on top of a major fault.

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.

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.)

Of all the earthquake prone regions of the world, the San Francisco Bay Area is among the most prepared structurally for the eventuality of a major quake while remaining grossly unprepared in both civil response planning and in the retrofitting of older buildings.

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 The Tom Wolfe novel A Man in Full features a fictional major earthquake on the Hayward Fault as a deus ex machina method (freeing a major character from prison) and plot development point.