It doesn't happen very often that a seismologist actually gets to observe a seismic wave in nature. Sure, we all sit in front of computer screens and look at the digital representation of the wiggles a seismometer produces. And indeed, the seismometer's mass swings with the rhythm of the wave. But these seismograms are far from the real thing. The blogger actually saw a seismic wave 20 years ago today, when the Loma Prieta Earthquake shook the Bay Area. I remember that it was a balmy afternoon. Everybody was excited because the A's and the Giants had lined up in Candlestick Park (as it was then known) for the third game of the 1989 World Series. I was in the car, picking my son up from after-school activities and dropping my daughter off for soccer practice. We were parked in her school's parking lot when the car suddenly began to rumble and then sway. I thought my son was jumping up and down in the back seat, eager to get home and watch the game on TV. But when I looked in the rear view mirror, I saw him sitting there quietly, staring awestruck out the window. When I looked in the same direction, I saw the asphalt in the parking lot swell and heave as though a giant gopher were digging through the earth at lightning speed. The wave in the asphalt was rapidly moving in our direction; it swayed the car up and down and within a few seconds - it was gone. I think the wave's crest was a few inches high, but everything went so fast that my recollection is somewhat blurred.

	Shaking intensity map for the 1989 Loma Prieta earthquake. Courtesy of CISN. (Click to view larger image.)

That was a seismic wave, I exuberantly told my son. It probably was a once in a lifetime event to really see one coming and going, I beamed at him. But he was not at all impressed, and asked coolly, why I had turned the car radio off. I knew I hadn't, but indeed, there was no sound. That moment I realized that something big must have happened. My car radio was still on, but the radio station had gone off the air. My thoughts began to race: If I can actually see a seismic wave from an earthquake in the parking lot, then the shaking must have been really severe. Was the rest of my family safe? Was my house ok? We grabbed the daughter and drove home, where we found everybody shaken and stirred, but safe and sound. Then, ever so slowly, the news about the destruction at various locations in the Bay Area began to trickle in. The rest, of course, is history. The quake had a magnitude of 6.9, a total of 63 people were killed, and more than 3700 were injured. Its hypocenter lay along the San Andreas Fault in the Santa Cruz Mountains near the Loma Prieta summit, 11 miles beneath the surface. The Cypress structure of the 880 freeway in Oakland had collapsed, parts of the Marina District were burning, one section of the upper deck of the Bay Bridge had fallen onto the lower deck, and there was widespread damage in Watsonville and Santa Cruz.

These are the terrible facts, but in a way are just statistics to the blogger. What he remembers vividly is the wave in the parking lot. I am sure other people must have had similar experiences on that fateful October afternoon 20 years ago. Please tell the blogger what you remember about the largest quake in the Bay Area since 1906. Email us at by going to "contact" at the top of the page or by writing to "blogger@seismo.berkeley.edu". (hra046)