Posted Fri., April 11—Is the Hayward Fault, which runs diagonally through Berkeley, a “tectonic time bomb in our back yard”?
Although he’s a scientist not given to hyperbole, the answer is essentially “Yes” says Professor Roland Bürgmann, a researcher at the Berkeley Seismological Laboratory, who delivered that sobering conclusion in the annual Lawson Lecture Wednesday, April 9, on the UC Berkeley campus.
The Lawson Lecture series was started several years ago during the build-up to the centennial commemoration of the 1906 San Francisco earthquake. The lecture will be reprised for the public on Cal Day tomorrow (Saturday).
Bürgmann led his audiences through both scientific analysis and a layperson’s layout of how the Hayward Fault acts and what impends for local communities in coming years.
The Hayward Fault runs northwest to southeast along the base of the Berkeley Hills. In most places it “represents the topographic front of the hills,” where the steeper sections give way to the much gentler incline of the misnamed “flatlands” of Berkeley and neighboring communities.
In 1868, the southern section of the Hayward Fault delivered what Bürgmann notes was called The Great San Francisco Earthquake for nearly 40 years, “until the 1906 earthquake stole its name.”
1868 was the year the University of California was chartered. There were barely a quarter million residents in the Bay Area at the time, and most of the East Bay, including the future Berkeley, was very sparsely populated.
Still, 30 people died and the quake’s namesake community of Hayward and other villages in southern Alameda County were wrecked, along with many buildings in San Francisco and elsewhere.
Geological studies focusing on the UC Berkeley campus area have shown that the west side of the Fault has moved at least 335 meters north, relative to the east side, over millions of years, at a rate of about 10 millimeters per year.
Strawberry Creek is offset considerably from its westward course when it hits the Fault at the mouth of Strawberry Canyon. Memorial Stadium is now constructed on this site, but the creek used to make a distinctive jog to the northwest, tumbling down a series of cascades and pools, before resuming its westward flow through the lower campus.
The Hayward Fault, Bürgmann noted, has had a typical “creep” of several millimeters a year, documented in features like the creek displacement but also, today, in offset curbs and broken paving up and down the East Bay, and the slow shift northwards of the western half of Memorial Stadium.
It’s not the creep that’s the problem, however, but when the Fault “locks” deep below the surface, building up strain that is then periodically and violently released in earthquakes.
Since the early 1300s there have been at least five major earthquakes on the Hayward Fault, at intervals estimated to be approximately 155, 160, 95 and 143 years. Since the 1868 event it has been “139 years and counting,” Bürgmann noted.
Thus 2008 takes on symbolic significance-it’s marks the end of the average 140 year interval between Hayward Fault earthquakes during the past several hundred years.
That doesn’t mean that an earthquake will occur this year. But it does mean that the next Hayward Fault earthquake is coming ever closer, no longer a remote possibility but a projected likelihood within decades, if not years.
Drawing data from several research approaches, “the Hayward Fault is ready today” for an earthquake, Bürgmann concluded.
His lecture was supplemented by an elegant combination of graphics-both still and moving-showing the wide range of tools seismologists can employ today to map and analyze the Hayward Fault.
Even if the subject weren’t so close to home for those of us in Berkeley, this was a fascinating lecture. The explanations of both traditional and revolutionary new research techniques were clear and intriguing.
There were aerial photos and computer generated topographic images showing fault strain from above and the side. These were as vivid as if the fault was a living organism subjected to an MRI.
One aerial showed hundreds of points in Berkeley where movement caused by fault creep or slow-moving landslides could be documented by satellite. Other images expanded out to the regional scale, documenting how the Pacific Plate beneath the ocean is moving north, relative to the North American Plate beneath most of the Bay Area.
As the Pacific Plate moves north, it is pulling part of central and southern California along with it. “Ultimately, Los Angeles will be ruining our views” to the west, Bürgmann joked.
However, even with all the detailed study of the Hayward Fault, “the earth doesn’t really behave the way we think it should,” Bürgmann notes. Earthquakes don’t come like clockwork.
But “we have clearly reached the stress load that was sufficient to cause the last two earthquakes on the Hayward Fault.”
Bürgmann closed his lecture with a quotation from Andrew Lawson, the renowned Berkeley geologist who named the San Andreas Fault and founded much of the science of modern seismology.
“The best protection against the danger of earthquakes is not the knowledge of the particular dates upon which they will occur, but the realization that they may occur at any time, and that foundations and structures should be built sufficiently strong to withstand the shocks,” Lawson wrote in 1922.
“Preparing ourselves for earthquakes is more important than all the earthquake prediction we can do,” Bürgmann concluded.
You can learn more about the Hayward Fault and earthquake safety at the website of the 1868 Hayward Earthquake Alliance, a consortium of organizations organized to commemorate the 140th anniversary of the 1868 earthquake, at http://1868alliance.org/
The Berkeley Seismological Laboratory, with a wealth of earthquake related information, can be found on-line at http://seismo.berkeley.edu/