Today is the 20th anniversary of the Loma Prieta ( M = 6.9) earthquake nearby on the San Andreas Fault in the Santa Cruiz Mountians. It happened at 5:12 in the afternoon and resulted in 65 deaths and billions of dollars of damage. It disrupted the transportation grid for a time because of two major collapses of bridges that saused most of the deaths. The result has been on-going seismic retrofitting or replacement of structures that could be affected by a similar event on another fault.
Geologists are expecting another event of a similar size somewhere on the Hayward-Rogers-Creek fault that runs from Fremont in the south, along the base of the Diablo Range in the East Bay, across San Pablo Bay up to Santa Rosa. There are actually related shears that follow a similar trend, all connected to the San Andreas Fault near Hollister, the Calavaras fault, on which there was a small quake within the week and the Heildsburg Fault north of Santa Rosa. The Hayward splits off from the Calivaras which bends off to an eastward roughly parallel trend. The other two faults are in the same trend as the Hayward and my be mere extensions of it.
Anyway, I was in a reinforced concrete room, probably a bunker, at SRI International that served as a machine room/terminal room for a set of Sun Workstations and servers. I had just walked in the room when the shaking started. I got down under a table under of big 19" color conitor, a CRT, (there were no flat panels in those days), that I hoped didn't walk off the table and crash down, and rode out the primary energy. What I recall next was feeling the long period elliptical waves, the Reyleigh waves, causing the sold concrete floor to feel like a water surface. When that was over, the lights went off and a UPS had burned out causing the systems, Sun4 servers and Sparc Workstations to crash. I guess there was a futile effort to reboot them and then an effort to secure them, powering all the servers off, and we left a few moments later.
We had an engineer who had done work in acoustic profiling. He was really a seismologist who knew the math in common with our work and what is done for seismic reflection, what is called the Multipath Problem. He came charging out if his office and said to me: "Did you feel those Ellipticals?". I said that I had. I remember barrowing Richter's Seismology from him, which I remembered reading a couple of days after.
I walked home on what had been a nice warm Fall afternoon to my duplex a couple of bloack away. We still had power which we did not lose even though neighborhoods all around us were out for hours after. I remember seeing my wife and eldest child, whom I had to admonish to put on shoes as he was barefoot and I had sweped up broken glass from the kitchen. I asked my wife what her experience had been. She was in a playground over on Willow Road and said that she saw the tan bark dancing around on the ground. She did not see ground waves. About a half hour after the main shock was the biggest aftershock, as I recall, whose magnitude was reported later to be 5.7. When it happened I knelt down to feel the gound, and again felt Reyleigh waves.
We gradually learned how serious this event had been in other areas, as it did not seem to us to have been as big as it turned out. We heard on the news about the Marina District in San Francisco, about the building collapses and fires, and about the Cypress Structure callapse and the loss of life there, and how it had stopped the World Series which had the Oakland A's and San Francisco Giants at Candlestick Park for the first game.
In the next few hours we heard of damage at Stanford University, mostly to the Inner Quadrangle and Memorial Church, but ironically, that the Geology Corner was one of the most seriously damaged places. The School of Earth Science was mostly in the newer reinforced Mitchel Building, which had little danage, but the second floor of the Geology Corner had partially collapsed. When I was a graduate student under John W. Harbaugh, the father of the Quarterback Jim Harbaugh, who is now the foot ball coach, I had my office there. I recently talked to some women who worked at Stanford and asked them about what was lost there, they wern't too knowledgable. I remember that it took a couple of years to fix the damage. It was some time before the Church could be used, and I remember repairs made to columns and arches in the Inner Quad.
One of the most widesparead problems was falling bookcases in the libraries at Stanford and around town in book stores. The building where Kepler's books and Cafe Barrone now live was built in 1989 and opened about a month before the quake. Book cases in the newly moved bookstore fell down. The cafe hadn't opened there until December of 1989, so it too is comming up on its 20th anniversary. I think the date is December 11, so it will be interesting to see how that date is commerated.