JONATHAN BRAY admits it’s not easy describing his job. His title at UC Berkeley, professor of geotechnical engineering, can leave a listener scratching his head.
“The science is focused on engineering systems that are supported on or within the earth,” he said. “Whether it’s foundations for buildings, building an earth dam or constructing a lifeline like a highway, we have to understand the stability of the geology, the soil and the rock.”
So, you might say he plays in the dirt — except his findings help determine whether a building can withstand an earthquake. And, as much as we like to ignore the fact, a big one is going to strike someday. Bray’s studies take him to ravaged sites — he visited Chile after a magnitude 8.8 temblor struck in February — to determine where and why structures did or did not survive.
“We look at how the ground affects the response of the structures,” he said. “We look at how bridges respond. We examine the decks and the supporting piers. We ask why one structure was damaged and another was not.
“The broad category is effects — how soil conditions change the ground shaking, and we look at the phenomenon of soil liquefaction.”
Ground-motion prediction is perhaps the biggest recent advance in earthquake science. Sensors that recorded ground vibrations in the Loma Prieta (1989), Northridge (1994) and Taiwan (1999) earthquakes helped develop ground-motion models used today.
“The key to designing the new Bay Bridge is knowing what it’s going to be like in an earthquake,” Bray said. “Is the soil going to liquefy? Is the ground going to move back and forth just a few inches or a few feet? The input to answering those questions is knowing how hard the ground will shake.”
Engineers have learned so much from on-site examinations that it is now possible to stabilize otherwise unsafe ground by mixing it with cement or driving vibrators into the soil. Studies also have laid the foundation for new construction techniques and advanced building codes.
The benefits are as easy to identify as the divergent outcomes of two landmark events in 2010. On Jan. 12, when a magnitude 7.0 earthquake struck Haiti, an estimated 230,000 people were killed. On Feb. 27, when a much larger 8.8 temblor hit Chile, only 300 deaths were recorded.
“In Chile, you have well-trained engineers and a modern building code that’s very much like ours,” Bray said. “Haiti really doesn’t have any codes.”
Bray, whose office sits along the Hayward fault, says earthquakes are inevitable. The last forecast by the Working Group on California Earthquake Probabilities reports a 62 percent chance of a major earthquake in the Bay Area by 2031.
Scientists can only hope to mitigate the damages. Early-warning systems, for instance, which can identify a fault break a few seconds before the damaging shear wave strikes, could warn emergency responders and enable infrastructure operations such as BART and Caltrans to take actions to minimize damage.
One of Bray’s current projects, dubbed “iShake,” utilizes smartphones in identifying regional earthquake activity.
He explained that the same component that enables the phones to play games — an accelerometer — is capable of ground-motion detection. With the iShake app, now in a pilot phase, phones some day will be used to relay information about the location and intensity of an earthquake after a major event.
The Bay Area, riddled with faults from San Andreas to Hayward to Mount Diablo thrust, is assured of seismic activity.
About which should we be most concerned? According to our expert, all of them.
Contact Tom Barnidge at tbarnidge@bayareanewsgroup.com.
