Like nearly everyone who lived through it, Anne Kiremidjian remembers exactly where she was during the 1989 Loma Prieta earthquake: idling on Foothill Expressway as she prepared to turn left onto El Monte Avenue.
She felt a jolt and presumed another car had struck hers. But the next vehicle was far away. She watched the traffic light shake violently. But no breeze blew. Then the six lanes of traffic around Kiremidjian began to dance.
“I could literally see the cars going up and down and up and down as the wave crossed,” she said. “It was fascinating. Absolutely incredible.”
The Los Altos Hills resident, a professor of civil and environmental engineering at Stanford University, related the anecdote to an audience of approximately 75 gathered at town hall May 1 for the forum “Everything You Ever Wanted to Know About Earthquakes But Were Afraid to Ask.” Her presentation detailed what causes seismic activity, how it impacts structures and how historical quakes stack up against one another.
The local bad boy is the San Andreas Fault, which runs for approximately 800 miles between Cape Mendocino in Northern California and the Salton Sea in Southern California. Contrary to common belief, Kiremidjian said, the fault is not a single line but a zone where the North American and Pacific tectonic plates move relative to one another. When enough energy accumulates to overcome the friction between the plates, an earthquake occurs.
The San Andreas Fault’s most infamous offspring, of course, are the 1989 Loma Prieta and 1906 San Francisco earthquakes. Kiremidjian refers to the 6.9-magnitude, 15-second-long Loma Prieta as “a baby” compared to its 1906 predecessor, which scientists estimate measured between 7.7 and 7.9 in magnitude and lasted up to a minute; whereas Loma Prieta ruptured along the fault for approximately 25 miles, the 1906 event ruptured the 296-mile stretch between Cape Mendocino and San Juan Bautista.
“Just picture in your head almost 300 miles of earth moving at the same time and the amount of energy that’s required to move that massive earth simultaneously and the amount of energy that’s released from that kind of event,” Kiremidjian said.
Slippage, or ground movement along the fault, reached 25 feet near Shelter Cove.
“Imagine me being shoved to your right 25 feet in a few seconds – in literally seconds: Just, phew!” she said. “I’d be flying. … We need to take this guy very seriously. It’s not a joke.”
The 1906 quake acted as a sort of “all-emptying event” that cleared decades of accumulated seismic stress, Kiremidjian said. United States Geological Survey (USGS) models estimate that it could take until 2106 before a comparable quake ruptures along the fault.
Kiremidjian said the next local “big one” will likely occur on the Hayward Fault, which runs along the foot of the East Bay hills and is part of the San Andreas Fault System. It experiences a major earthquake every 161 years, plus or minus 65 years, and the last significant one, estimated at between 6.8 and 7.0 magnitude by the USGS, struck in 1868.
There is a 68 percent chance of another major Hayward Fault earthquake in the next 28 years or so, Kiremidjian said.
Would a warning system work?
So, an audience member asked, should the U.S. follow Japan’s example and develop an early-warning system capable of pushing alerts to cellphones seconds (and sometimes minutes) before an earthquake?
Such tools could be useful if alert recipients are miles away from the rupture zone, a luxury local residents likely won’t have, Kiremidjian replied.
“We are close to the San Andreas Fault, so for us, it won’t make a difference. By the time an early warning comes to us, it’s over,” she said.
Her response to the question was a valuable takeaway from the presentation, said forum attendee Peter Evans.
“You should be prepared, now, rather than five seconds before it happens,” he said. “I thought her answer to that was really good. So, it’s kind of like, are these technologies going to save us? No. Store up your water.”