The Hayward Fault and Cal Memorial Stadium
Recently, the University of California, Berkeley won against an injunction that was preventing it from constructing a new training center for their athletic department, as well as retrofitting and improving the historic Cal Memorial Stadium. One of the reasons Cal Memorial Stadium is so well known is that it sits directly on top of the Hayward fault, and is actually being split in half due to creep along the fault.
Some of you might be slightly familiar with this story, as much of the attention was focused on a group of tree-sitters who took up residence in a grove of oak trees next to the stadium in order to protest and protect the grove from removal. Their complaints included the age of the oaks, previous claims of a native American burial ground and that retrofitting a stadium that sits directly on top of the dangerous Hayward fault is not wise. After two years, the tree sitters were removed last month and construction has finally begun on the new stadium.
In an Op-Ed piece from yesterday, an emeritus professor of geology at Cal weighs in on construction at Memorial Stadium and explains the local geology of the area.
First, the geologic setting of the two areas: The active Hayward Fault goes across the mouths of both canyons. Further east, the Wildcat Canyon fault parallels the Hayward Fault behind the Botanical Gardens and northward joins the Hayward near the town of San Pablo. Southward the Wildcat Canyon fault can be easily traced to Sibley Park and beyond. A few small epicenters lie along this fault near its junction with the Hayward, but it does not seem to be active elsewhere to the south. However, in the past the area between the two streams and the two faults, which includes the whole of the Lawrence Laboratory complex, lay four miles to the south next to Sibley Park.
The volcanic rocks in both areas have potassium-argon dates of approximately 10 million years, and the rhyolite found in both of them is the same rhyolite. The volcanic rocks underlying most of the Lawrence Lab complex fill an old crater, a collapse caldera. The old volcano that once rose above these rocks collapsed after the expulsion of a very large amount of rhyolite ash, now largely removed by erosion. The volcanic rocks broke up as the collapse occurred and many show crushing and deformation and are mixed with large amounts of ash and volcanic fragmental debris. This material should never have been built on as it is so clay-rich and unconsolidated. The western rim of this caldera is easily traced trom its arcuate shape which is cut off by the Wildcat Canyon Fault just south of the Botanical Gardens near the upper part of Strawberry Creek.
Lennart was able to get survey notes from East Bay Municipal Utility District for the San Pablo Dam water tunnel to El Cerrito which crosses the Hayward Fault and shows that the right lateral horizontal movement of approximately one centimeter per year is matched by uplift of the east side of the fault of approximatelly one centimenter per year also. So, with the evidence of the horizontal displacement of the old Strawberry Creek of 600 feet horizontally along Galey Road, the Cretaceous sedimentary rocks east of the Hayward Fault there have also risen 600 feet . Building 50(?) sits on these Cretaceous strata which, as mentioned dip westward 20-25 degrees. If an earthquake occurs when these beds are soaked with winter rains the chance of a major landslide are great along the slippage planes of shale dipping westward. Minor slides have already occurred in these beds behind Bowles Hall. Indeed, the Foothill Student Housing was planned to be built there until I called attention to the landslide. A major landslide would probably destroy all the buildings on both sides of Galey Road from the Stadium to the buildings on both sides of Hearst Avenue and would probably reach Dow Library, destroying everything in its path to that point and possibly beyond. Buildings in the lower parts of both Strawberry and Blackberry Canyons would be buried if not destroyed.
Major landslides of the type I have described here are not rare along the Hayward Fault, as was shown to us during our study of the Hayward fault at the base of the hill behind the Clark Kerr Campus. We discovered that most of that campus was underlain by a large landslide that had originated in Claremont Canyon, and was gradually moved northward along the Hayward Fault. Trenches and drill holes showed this landslide to be up to 30 feet thick. It extends westward to and possibly beyond Piedmont Ave. Further south is a huge landslide that underlies most of the campus of Mills College and extends westward another quarter mile Still further south are more large slides that have originated in canyons and steep slopes east of the Hayward Fault. As the hills rise and become unstable, earthquakes cause them to break loose and slide. Very few large slides have occurred on the eastern slopes of the Berkeley Hills, hence the relationship to earthquakes of major land slides close to the Hayward Fault along the western slopes of the Berkeley Hills. Normal erosion rounds off unstable areas on the eastern slope of the Berkeley Hills before they break loose and slide.
The Berkeley and Oakland hills are famous for their instability. This article from 2004 talks about the shifting ground in Berkeley and the effect on property lines.
Scientists have mapped and studied slow-moving slides in California for decades, and there are thousands in the Bay Area, said Richard Pike of the U.S. Geological Survey. Most move only as a result of moisture or disturbance.
In June, an international team including UC Berkeley scientists reported that large tracts of East Bay land typically move between 5 and 38 millimeters a year.
Land movement in Berkeley has wrecked home foundations, cracked walls and sidewalks, buckled streets and fences and frequently ruptured water lines. Some homes stand abandoned, and others have been rebuilt with massive and deep foundations.
But the impacts on property lines in urban neighborhoods have been discussed very little, Pike said.
“I’m surprised nobody figured this out earlier,” he said. “As more people build in the hills, you’re going to see this problem get larger and larger and larger.”
Howard Brunner, a consultant to the state agency that regulates land surveyors, said there is no state law specifically designed to address property-line disputes where the ground is slowly moving.
[Via Ontario Geofish]
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