U.C. Berkeley Campus Hayward Fault Field Trip Highlights Life along an Active Fault Line
Peggy Hellweg, Doris Sloan and Christine Shaff, UC Berkeley, and Don Wells, AMEC-Geomatrix ― November 15, 2008
Text and photos by Dan Day, from the May 2009 newsletter
Over thirty NCGS members and their friends attended the November 15, 2008 U.C. Berkeley Campus Retrofit and Hayward Fault Field Trip featuring a tour of the UCB Seismological Laboratory. Trip Leaders Peggy Hellweg of the UCB Seismological Laboratory staff, U.C. Berkeley Professor Emerita Dr. Doris Sloan, and University Administrator Christine Shaff prepared a beautiful guidebook featuring a tour of campus facilities and surrounding neighborhoods. They were assisted by contributing authors Donald Wells, Project Manager with AMEC-Geomatrix and Patrick Williams of San Diego State University. Under sunny, clear blue skies, the group trekked across the campus to view seismic retrofits, and through nearby neighborhoods to examine the Hayward fault trace. The University is concerned about seismic risk because experts believe the next significant Bay Area earthquake has a high probability of occurring along the northern segment of the Hayward fault.
Participants met at McCone Hall on the U.C. Berkeley campus, and then marched off to examine signs of the Hayward fault reflected by the local geomorphology and damaged man-made structures.
Figure 1 Field trip group assembled at McCone Hall, U.C. Berkeley.
Stop 1 was at Founders Rock, a silica-carbonate outcrop of highly altered serpentine, where a plaque commemorates the founders of the University of California, Berkeley. Peggy noted that a reliable water source prompted the founding body to select Strawberry Canyon as the University site. Large acreage was subsequently purchased by the University in this area. Founders Rock displays abundant slickensides on its exposed surfaces, subtly acknowledging its complex tectonic history.
Figure 2 Trip leader Peggy Hellweg of the U.C. Berkeley Seismological Laboratory at Founders Rock.
A short walk south along College Avenue took the group to the Foothill Housing Commons. This building was earthquake retrofitted. The second stop was at a nearby bus station where a stream channel exits the East Bay Hills. The channel has been “beheaded” or cut off from its drainage source by right lateral motion along the Louderback fault, a strike-slip offshoot of the Hayward fault. Chert debris found in the channel bottom indicates it was originally fed by Strawberry Canyon, which has chert-bearing horizons in its drainage basin. Strawberry Creek has been offset about 1,100 feet north on the west side of the Hayward fault.
Discussions of relative plate movement and displacement rates were held at this stop, by the Foothill Housing Commons. Regional GPS measurements indicate there is about 5 cm per year right lateral movement between the Reno, Nevada, baseline station and its sister station on the Farallon Islands. Gradually partitioning this motion along Bay Area strike slip faults yields a 1 cm/yr creep rate on the northern segment of the Hayward fault. Trenched carbon-14 dates of exposed fault features in displaced stream channels feeding Strawberry Canyon east of the Hayward fault give offset dates at 35,000 yrs. B.P., 45,000 yrs. B.P., and 60,000 yrs. B.P. These dates represent the times when these channels were “beheaded” by right lateral motion along the fault. Active tectonic creep along the Hayward fault continues today.
Leader Peggy Hellweg noted that the larger the earthquake magnitude, the greater the relative displacement along the fault. She also pointed out that the Berkeley Hills are an expression of compressive forces acting on land sandwiched between the Hayward fault and the Calaveras fault to the east.
The third stop, at the corner of Gayley and Rimway, allowed Don Wells of AMEC-Geomatrix to discuss the geotechnical work his firm has accomplished over the years to assess and remediate seismologic structural damage on the campus. Don described the overall project and the details of tectonic activity in the vicinity. Peggy added comments regarding seismic behavior in the Berkeley Hills and its relationship to large scale deformation between the Pacific and North American Plates.
The group reassembled at the fourth stop, a basketball court just south of Bowles Hall, where extensive fault trenching has been done. Don Wells described the trenching activity for the campus housing in this area. Twenty trenches were dug to locate the Hayward fault trace, which was revealed by ground rupturing and deformation after the 1868 Hayward earthquake. Recent trenching began in 1992. The east and west fault traces were located but portions were obscured with colluvium and alluvium that had washed down the hillside. Some of this debris may be landslide material. In some cases 1915 aerial photographs were consulted to determine bench locations. Here a sliver of Cretaceous Knoxville Formation is exposed resting on the Coast Range ophiolite. Professor Garniss Curtis of UCB interpreted some of the units in this vicinity as a shale matrix mélange. Don Wells suggested it may be a “flower” structure squeezed up along the Hayward fault strike-slip zone.
The Hayward fault trace was located near Bowles Hall, constructed on a hillside fault bench in 1927. The old building has no structural damage, but the Hayward fault passes beneath its southeast corner. In the interest of seismic safety, Bowles Hall will be structurally decoupled from the fault to allow right lateral ground creep movement beneath it. The group walked south from Bowles Hall to examine nearby street curb creep displacement, and then strolled to Memorial Stadium.
The tour lingered a while at Berkeley Memorial Stadium. Don Wells elaborated on its structural damage and described detailed mapping that AMEC-Geomatrix has done to assess the local geologic structures and stratigraphy. These studies were used to develop a stadium remediation plan to minimize future structural damage. The challenge is to minimize the effects of 4.5 mm/yr shear along the Hayward fault.
Figure 3 Tension cracks on the side of the Berkeley Memorial Stadium north entrance.
At the north stadium entrance, Peggy Hellweg pointed out a U.C. Berkeley Seismology Laboratory monitoring station. This is the Laboratory’s closest station to the Hayward fault. As the group entered the stadium, Don Wells noted diagonal shear fractures on the stadium wall that are attributed to fault movement. The Memorial Stadium was constructed in 1923 in six separate sections. The builders were cognizant of local fault activity and chose this design to minimize seismic damage to the structure. The stadium was built on fill in Strawberry Canyon, and was buttressed up against a shutter ridge on the southwest side. Some stadium sections have perceptibly rotated with respect to one another.
Figure 4 Large fracture in the wall at the north Berkeley Memorial Stadium entrance below the bleachers.
The stadium shows additional damage at its southwest end. In plan view, the stadium has been constructed adjacent to a shutter ridge which deflects Strawberry Creek northward, forming a natural amphitheater. Excavation into the northern part of the hillside provided fill for the stadium, and the ridge itself supports the southern end. A 36-inch diameter culvert was built under the stadium to handle flow from Strawberry Creek, and when that was found to be inadequate, another was built around it. A deformation zone in the culvert underneath the stadium marks the Hayward fault crossing. The stadium site was chosen for its view across the San Francisco Bay and because it afforded the least excavation. Shutter ridges play an important geomorphic role along the Hayward fault. Lake Temescal was formed behind one, and the Claremont Hotel rests on another.
A large gap has opened in the southwestern stadium wall, as illustrated in Figure 5.
Figure 5 Large gap in the southwest wall of Berkeley Memorial Stadium.
Underneath the stadium bleachers at the south end Don Wells showed the group offset along support pillars where two adjacent stadium sections moved relative to each other (Figure 6). The proposed fault crossing is south-southeast of this point but the deformation has been transferred here. The geologic cross-section across the Hayward fault at the stadium has a highly sheared zone sandwiched between colluvium and alluvium. This may represent a “flower” type structure along a strike-slip fault where material is squeezed up along a vertical fault plane in response to shearing forces. This feature is common in the California Coast Range.
The clayey fill under the stadium was very well compacted, dense, and not prone to liquefaction. However, NCGS member Jeffery Shaffer, a Geology Department faculty member at Napa Community College, presents a convincing argument that the damage is due to settling and not necessarily to fault activity. Regardless, the stadium has clearly suffered significant structural damage.
Figure 6 Offset along pillars underneath Berkeley Memorial Stadium.
Because of these visible flaws, the University of California hired AMEC-Geomatrix to design a seismic retrofit for the stadium. The consultants noted that the north end needs rebuilding, and the south end reinforcement. The master mitigation plan is to drill holes and cast pillars (pilings) underneath the stadium where the Hayward fault is thought to cross, add a layer of plastic on top, and cap this with a concrete slab that would decouple the stadium from the underlying ground. The pillar system would be free to slide under the stadium. The overlying slab would be constructed of steel-hinged segments that would articulate freely with creep activity along the Hayward fault.
Carbon-14 (C14) dating of samples taken on a transect beneath the stadium indicate the colluvium layer is over 45,000 years old, and that the top few feet of cover is only a few thousand years old. The Hayward fault trace lies under the southwest stadium expansion joint, but the creeping fault segment is further southwest. As the group exited the stadium, Don noted that the west stadium end rests on siltstone bedrock.
The group stopped briefly to examine a crack in a large concrete slab on the ground level parking area beneath an apartment complex at Bancroft and Prospect. This building lies immediately south of the stadium, and the crack is interpreted to be evidence of Hayward fault creep.
A couple blocks further south on Prospect, the group turned east and went up Hillside to follow Hamilton Creek. The gulch it carved is offset right-laterally by the Hayward fault.
Going south towards Dwight Way, the tour passed the Smythe home. The now deceased Mr. Smythe wrote articles for the local newspaper chronicling the construction of Berkeley Memorial Stadium in the late 1920s. Further south the Hayward fault was multiply-trenched across a parking lot in 1992, revealing a well-defined fault zone. The parking lot and the adjacent Fernwald Housing complex have been replaced due to seismic risk (the building had been strongly deformed by fault creep). Now a new building and a vegetable garden occupy the site.
The tour emerged on east-west trending Dwight Way, on a steep stretch represent the Hayward fault scarp. Right-lateral curb deformation is obvious where the street crosses the fault trace (Figure 7).
Don Wells mentioned that although there are many obvious geomorphic and anthropo-morphic expressions of creep deformation along the Hayward fault, many important natural features have been eradicated by human construction. Hence, consultants like AMEC-Geomatrix have had to consult old aerial photographs for valuable geomorphic information. Don also noted that LIDAR (light detection and ranging) images have been marginally useful to his firm because of the ground disturbances caused by building construction. As the group passed the site of the new U.C. Berkeley Athletic Center, scene of the recent oak tree protests, Peggy Hellweg pointed out an old rhyolite boulder retaining wall that has been in place for decades, and shows no signs of fault displacement.
The field trip returned to the U.C. Berkeley campus and made another stop at Strawberry Creek near Hildebrand Hall. This wooded glen is west of the Hayward fault. Strawberry Creek flows year round here and has been displaced about 1100 feet northward by right-lateral motion along the Hayward fault.
Figure 7 Curb offset on Dwight Way looking downhill (west). Red arrow notes general vicinity of creep offset on the Hayward fault.
The trip broke for lunch outside Evans Hall, where U.C. Berkeley administrator Christine Shaff detailed the University’s efforts to seismically retrofit key campus structures. After the 1989 Loma Prieta earthquake, the U.C. Berkeley admini-stration felt compelled to assess its seismic safety. The University had been aware of Hayward fault creep in the 1980s, and had done some seismic retrofitting of its infrastructure. The post-Loma Prieta seismic survey ranked 27% of the square footage poor to very poor, using the current U.C. Regents’ rating system. Some of the buildings surveyed have to meet higher retrofit standards because they have to be functional in the event of an earthquake. These include the University computer facility, health services buildings, and dining commons (for feeding and sheltering people from the University and surrounding communities).
In 1997, U.C. Berkeley established a 10 point action plan. This plan focused 10% of its budgetary resources on seismic safety. Since 1997, 50% of the targeted campus structures have been retrofitted. The present focus is on the next 25%. There are currently no occupied campus buildings that are rated poorly. The project has allowed the University to design many innovative methods of addressing seismic safety and structural reinforcement, such as shear walls. Now there is plenty of space to house people in the event of an earthquake disaster, based on current USGS predictions of probable earthquake magnitudes. The plan also provides for instruction to continue on the campus while damaged buildings are being repaired. The 10 Point Plan will also review and revise campus disaster preparedness measures.
U.C. Berkeley considers seismic issues a priority and has placed a university Vice Chancellor in charge of implementing the 10 Point Plan. The Vice Chancellor’s duties include (1) delivering and streamlining the management of campus capital improvements and (2) maintaining focus on seismic safety and on disaster preparedness and response. The University has constructed buildings and facilities with shared equipment that will be available to departments in the event that their buildings are rendered unusable. The 2009 California State budget crisis has forced the delay or rescheduling of some retrofitting projects. Damage models have been made based on retrofit structural designs. A key factor in this program, said Christine Shaff, is that U.C. Berkeley is one of the largest employers in the East Bay. The local economy cannot afford to have it closed down.
In addition to items mentioned above, the 10 Point Plan has addressed all non-structural seismic hazards. The retrofitting concept involves protecting laboratory equipment and supplies as well as structures. And the U.C. Berkeley Emergency Awareness Program addresses fire, power outages, hazardous chemical releases, and bomb threats in addition to earthquakes.
After this excellent introduction, the field trip group toured the Hearst Mining Building. This is an older facility built in 1907 and designed by UCB Architecture School professor John Galen Howard under an endowment from Phoebe Hearst. The Hearst Building retrofit is a base isolation design. This is structurally less intrusive, but expensive to accomplish. The building rests on rubber bumpers or cushions to “isolate” it from the ground beneath. The entire building had to be raised off its foundation to insert the cushions, then lowered onto them. A concrete moat was constructed around the building to contain it and keep the suspended structure from impacting horizontally against the ground. It has been designed for a magnitude 7.0 earthquake on the Hayward fault. This design was used for other campus retrofits and has been applied in Japan. The 60 million pound building rests on 134 base isolators fitted with accelerometers (see Figure 8). Other accelerometers and 25 seismometers have been positioned elsewhere in the building. This is [as of 2008] the only instrumented base isolated building in the world. Fortuitously, engineering facilities on campus are equipped with large shake tables that can be used to model campus retrofit designs. The utilities in the Hearst Building are designed to move freely in an earthquake. The interior and exterior brickwork was removed, cleaned, and reattached. During this and other retrofits, the occupants were temporarily housed in an “overflow” building on Hearst and Oxford until the retrofit was completed. The tour also stopped at the now closed Lawson Adit, a tunnel used for mining engineer instruction that crosses the Hayward fault to the east.
Christine Shaff continued to lead the campus building retrofit tour. After leaving the Hearst Mining Building, the group stopped at Latimer and Hildebrand Halls. Hildebrand Hall has inverted “V” beams attached to external concrete structures to anchor and stabilize the building. The Latimer Hall retrofit did not reduce the inner space of the building. It was considered susceptible to earthquake whipping action, so designers constructed an external concrete shell fastened to the outer structure to resist flexural forces. Hertz Hall was retrofitted to increase its north-south directional shear strength. Exterior tiles were removed, cleaned, and reattached.
Wurster Hall (College of Environmental Design) is a massive structure. Its external columns were strengthened with fiber wrapping. Barrows Hall was originally constructed with a discontinuous shear wall. The shear walls were made continuous, and concrete “bookends” were added to improve its shear strength. Sather Tower/Campanile is slated for retrofitting to strengthen the upper level viewing platform.
The oldest campus building, South Hall, was constructed in 1870 as an earthquake resistant edifice using building failures in the 1865 and 1868 San Francisco earthquakes as guidelines. It is an unreinforced masonry structure dubbed the “Mary Poppins building” for its resemblance to Victorian architecture. Its inner walls were tied together with steel bars and the roof structure was reconstructed to meet current earthquake codes. However, the original design was remarkably earthquake resistant, thus allowing most of the structure to be preserved.
Figure 8 Base isolator cushion and accelerometers underneath the Hearst Mining Building.
The Bancroft Library, adjacent to the Doe Library, was the most recent building to be retrofitted. It houses rare documents, books, and other memorabilia. The previous interior was “like a rabbit warren,” with twisting, intricate hallways. The entire interior was gutted and new floors were added to meet seismic requirements. A new HVAC system was installed for climate control. For accessibility needs, Bancroft Hall was attached to the adjacent Doe Library.
The final retrofitting stop was McCone Hall, home of the Earth and Planetary Sciences Department. McCone has also been retrofitted without sacrificing valuable interior space. Exterior walls were added to strengthen the structure. McCone houses the Berkeley Seismological Laboratory (BSL) on its second floor.
Seismology has a long tradition at U.C. Berkeley. In 1887 seismometers were installed on the campus near McCone Hall, and at Lick Observatory on Mount Hamilton east of San Jose. From this modest beginning the Berkeley Seismological Laboratory seismic network has grown to nearly 50 sites in California and Southern Oregon. It offers unique seismological research opportunities.
The BSL suite displays a seismometer given to Professor Andrew Lawson in 1913. Lawson did an exhaustive survey of structural damage and geomorphic features associated with the 1906 San Francisco Earthquake. His report on this work is a classic. On display are various research seismometers including a Benioff short period seismometer with a 100-kilogram mass, a Wiechert seismometer with a 160-kilogram inverted pendulum, and several Wood-Anderson seismometers used to establish the Richter magnitude scale in the 1930s. Over the Cold War years, BSL has monitored underground nuclear detonations for compliance with the Nuclear Test Ban Treaty.
Today 30 stations report to the main data center. Analog signals are converted to digital code and are processed. Berkeley enjoys the ability to monitor signals over a wide dynamic range and can therefore analyze a larger spectrum of sources.
In 1966, the USGS established its own seismology laboratory, which eventually grew to over 300 stations in California. With 10 times as many stations, the USGS can more accurately locate epicenters with better precision than BSL. But the USGS has a narrower dynamic range.
The Berkeley system’s sensitivity was revealed when its seismographs recorded signals from the December 26, 2006, Sumatran earthquake. This enormous event caused one centimeter of ground displacement in Berkeley and was continuously recorded on UCB seismometers for 5 minutes. Its waveforms made 10 global circumnavigations, and resonant modes were captured up to one month later.
Typically the BSL monitors earthquakes in the greater Bay Area. It can provide moment tensors, finite fault inversions, and waveform analyses. These are details that are used for research modeling applications. Relative fault motion and 3-D information can also be generated to characterize motion along the fault rupture, to determine fault rupture mechanics, or to measure ground offset caused by an earthquake. The BSL can characterize the structural features, layer velocities, elasticity and other crustal physical properties between the source and the seismic receiver.
Figure 9 Peggy Hellweg in the Berkeley Seismological Laboratory, McCone Hall, U.C. Berkeley.
Peggy finished with a discussion of California seismology history. The Southern California Earthquake Center was established at the California Institute of Technology in the 1920s by legendary seismologists Beno Gutenberg and Charles Richter. Monitoring regions between northern and southern California became very territorial. Eventually U.C. Berkeley seismologist Perry Byerly and Beno Gutenberg agreed to demarcate their territories with a line drawn between Morro Bay near San Luis Obispo and Bishop on the east side of the Sierra Nevada.
The USGS began seismic monitoring in the 1960s with their less sensitive but more numerous station system. In 2000 the California Integrated Seismic Network was established to share data between Caltech, the USGS, and the BSL. These institutions are slowly achieving a more cordial state of data sharing.
The Northern California Geological Society extends its sincerest thanks to Peggy Hellweg, Doris Sloan, Christine Shaff, and Don Wells for making this a truly memorable field trip. The hospitality of the University of California, Berkeley is gratefully acknowledged. This multifaceted look at the Hayward fault, the U.C. Berkeley seismic retrofitting program, and the University’s seismological capabilities was skillfully orchestrated by the trip leaders.