Hayward Fault Zone
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For recent activity in the region shown on this map see the USGS map for this location. The "live" maps will also show all of the names of faults shown on the map as you rollover with the cursor. |
The
Hayward Fault Zone is located in northern
California in the
San Francisco Bay Area. It is parallel to and east of its more famous (and much longer) sister fault, the
San Andreas Fault. To the east of the Hayward Fault lies the
Calaveras Fault and beyond that the
Clayton-Marsh Creek-Greenvile Fault and their northern and southern extensions via other faults. These four fault structures are the major
known active slip-strike
faults in California at the
latitude of
San Francisco.
The nearest aligned fault to the north, the
Rodgers Creek Fault Zone, is considered by many experts to be an extension of the Hayward Fault Zone in that a massive rupture may result in slippage on
both these fault segments as well as the currently undetermined connection between them - under
San Pablo Bay. If these faults are not
directly connected (as appears unlikely due to the depression at this location), an alternative overlapping parallel segment arrangement would still allow coupled motion of the two segments and would be consistent with the local (underwater) typography. The
Association of Bay Area Governments has prepared ground shaking maps that include this possible scenario (these are shown below to the right).
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USGS Satellite photo of the San Francisco Bay Area. Light gray areas are heavily urbanized regions |
As the
Pacific Plate moves slowly northward under the forces of
plate tectonics, the several faults shown on the map above are both
locked and
stressed and periodically one will rupture over some portion of its length, releasing energy in the form of
earthquakes. Most of the earthquakes are small and fairly frequent (in a geological time scale). The last truly major earthquake in the region was the
1906 San Francisco Earthquake, its 16 foot (5meter) fault movement on the San Andreas causing substantial destruction of masonry buildings prior to the subsequent and far more destructive fire in the city. Much of the substantial destruction due to ground motion in the larger region (other than the extreme devastation of
Santa Rosa) was little noted in the reporting. It is apparent that the 1906 earthquake reduced the stress on the Hayward fault, creating an "earthquake shadow". 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. 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 region. Lesser 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. Most aware residents just live with the conditions and are glad to not experience
tornados and
hurricanes. There is an element of
denial among most residents as they are largely under-prepared for a major event. A major event on either the Hayward or San Andreas could produce a minute or more or intense shaking, as was felt in the great
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 due to soil failure.
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Shake map for combined Rodgers Creek and northern Hayward fault slip, magnitude 7.1 |
The magnitude of an earthquake, as measured by the
Richter magnitude scale, is proportional to the length of the rupture, while the ground motion in a large region surrounding the fault is highly dependent upon the local soil conditions and (as recently recognized in the
Loma Prieta earthquake) reflected energy from deep discontinuities in the earth's structure.
The most recent major earthquake on the Hayward Fault occurred in
1868, well before the
East Bay region was extensively urbanized. Some believe that this earthquake may have in fact been of greater intensity than that of the San Andreas 1906 event, particularly insofar as its perceived ground motion is concerned.
For additional ground hazard maps similar to those shown at the right see
the ABAG map index for this location. Some maps on this site are for more specific regions within the larger area.
The surface of the fault is creeping at less than 1 cm (0.4 in) per year. This creep is insufficient to relieve the accumulating forces upon most of the fault and so will not prevent a large earthquake. The creep is sufficient to displace roads, curbs, and sidewalks and so reveal the surface trace in many locations. This may be seen particulary in older structures crossing the fault, some of which have been fitted with expansion joints to accommodate this slow motion.
For several reasons the Hayward Fault Zone is of considerable regional concern. The estimated probablity of a major earthquake within the next thirty years is estimated at over 30 percent, compared to about 20 percent for the San Andreas Fault, which can have larger earthquakes but which is likely to produce less destructive effects.
Bayside soil conditions
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Shake map for northern Hayward fault slip, magnitude 6.5 |
The Hayward fault is considered to be particularly dangerous due to the poor soil conditions in the
alluvial plain that drops from the East Bay Hills to the eastern shoreline of
San Francisco Bay. 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. This soil tends to amplify the effects of an earthquake and so producing significantly greater ground motion. Additionally, the soil itself can fail, turning into a liquid mud from the agitation, a mud unable to support buildings erected upon once-firm soil. This region is also covered with dense low-rise urban development, most of which was built soon after the
1906 San Francisco earthquake, but before good earthquake resistant construction practices had been developed. 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.
Ancient and prehistoric massive landslides
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Shake map for southern Hayward fault slip, magnitude 6.7 |
In addition to the bayside conditions, there is evidence of numerous archaic landslides from the Oakland-Berkely hills, with one believed as recent as 10,000 years ago, indicating the possibility that a large earthquake could trigger very large earth flows, particulary if the soils are seasonally saturated with water.
Highway 13
In its northern extent the Hayward Fault lies directly beneath the portion of
Highway 13 that is south of its intersection
Highway 24, with a number of elevated street crossings in the
Montclair District that are at each end founded on different major plates. The ultimate test of the effectiveness of retrofits applied to these structures will only come with a major fault movement here.
Highway 24
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Shake map for complete Hayward fault slip, magnitude 6.9 |
State Highway 24, connecting Oakland to Orinda 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 freway, and the plastic movement of the packed fill would likely distrupt the surface if the movement here of the fault is substantial, possibly presenting a hazzard to motorists and shutting down the highway for a while. More extensive disruption and greater hazzard would 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 retrofiting for safety.
Highways 80 and 880 and the Port of Oakland
A severe earthquake is more likely to disable the offshore causeway portions
Interstate Highway 80 (the
Eastshore Freeway), since it is built on fill placed atop mudflats whose upper layers were deposited in the 19th Century, during extensive hydraulic gold mining in the distant
Sierra Nevada mountain foothills. This soft mud is expected to amplify earthquake shaking, and the fill on top of the mud may liquefy, and so possibly cause major disruption of the highway due to failure by sinking and by differential movement of large sections. Similar conditions underly the eastern approach roads the the Bay Bridge. Better, but still poor soils underlie the portion of [[Interstate 880|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.
Highway 580
A major alternate route for trucks traveling south and east (only when highway 880 is disabled), this highway crosses the fault twice. An alternate access to this highway is via Highway 13, likely to be unusable as noted above.
Eastern span of the San Francisco-Oakland Bay Bridge
{{Image:EasternSFO OAKBrFromTI.jpg|thumb|left|200px|Eastern span and replacement construction}}Long recognized as likely to be severely damaged or even collapse in a major earthquake, a {{Eastern span replacement of the San Francisco-Oakland Bay Bridge|replacement eastern span is currently under construction}}. Completion is currently projected for late {{2010}}.
Lake Temescal
The fault continues north directly under {{Temescal Regional Park|Lake Temescal}} and its dam, which is unlikely to fail since it has been completely reenforced by the extensive earth fill supporting Highway 24.
Memorial Stadium
{{Image:MemorialStadium.jpg|thumb|left|200px|Memorial Stadium}}Further north the fault is under the centerline of the football field of {{Memorial Stadium, Berkeley|Memorial Stadium}} at the {{University of California, Berkeley}}. Fault creep since 1923 has offset the walls 13 inches (1/3 m). 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. Siesmic improvments are planned to coincide with extensive rennovations to the (football) player's facilities, spurred by the recent retention of a popular coach as part of his contract negotiations. The detailed nature of the seismic renovations have 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) where they pass over and near the fault, with appropriate sliding connections for the safety of spectators.
Some of the cities in the eastern bay shore and south bay region near this fault include
Richmond,
Berkeley,
El Cerrito,
Emeryville,
Kensington,
Oakland,
San Leandro,
San Lorenzo,
Castro Valley,
Hayward,
Fremont,
Milpitas,
Niles and portions of
San Jose.
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 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, etc.) and that much life-safety protective work remains to be done.
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Highway 24 retrofit at College Avenue Rockridge Bart parking.
Jacketed and grouted column on left, unmodified on right |
It is the likelihood of a severe earthquake on the Hayward Fault (rather than the San Andreas Fault) that has spurred a substantial effort to
retrofit and sometimes replace large structures at risk, particularly the eastern span of the
San Francisco-Oakland Bay Bridge, the
San Francisco and
Oakland city halls, the
Bay Area Rapid Transit under-bay tube
slip joint, 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
concrete costs due to the extensive construction work being done in
China.
In June of 2006
BART managment announced that they have elected to not modify the Berkeley Hills Tunnel, which actually penetrates the Hayward Fault, arguing that it would be cheaper 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.:
*Knowledgeable skeptics point out that the
a priori likelyhood (the combined
probability before the event) of a major local earthquake during a
world series baseball game
and that the game involve
two San Francisco Bay Area teams is almost vanishingly small, yet it
happened during the
Loma Prieta earthquake and so the event was covered in real time by the extensive nationwide television coverage in place for the game.
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Google Earth tour - screen snapshot over North Oakland and Berkeley |
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 unihabitable by a major event.
Fremont Earthquake Exhibit:
The Hayward Fault Exposed, July 15 - October 30, 2006.
The park containing this exhibit is three blocks southeast of the Fremont BART station. (
Google earth search "Sailway Drive, Fremont, California" for the exhibit location and turn on "Transportation" to show the station.)
* The exhibit is free and open to the public on weekends from 10 a.m. to 3 p.m.
* Weekdays the exhibit is open to groups by appointment, see the
city's web site for details and other information.
* The exhibit features a 12- to 15-foot deep trench exposing the Hayward Fault, which can be viewed "face to face" by descending a staircase.
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USGS Satellite Maps - Hayward Fault This includes links to the Google Earth virtual tour of the fault.
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"It's Not Our Fault"', article in the East Bay Express*
Bart seismic study document (PDF)*
The geology of "Bear Territory" - University of California at Berkeley geology tour
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Tour of the Hayward Fault - California State University at Hayward web site with images showing fault creep.
