Thursday, May 17, 2007

I Feel the Earth Move Under My Feet

I live in Earthquake Country and we had a fine little one yesterday: a nice, sharp boom-shudder that sounded and felt like a fully loaded cement truck had run into our living room. Somewhere in the house, something I still haven't found fell off of something else and hit the floor. My wife and I looked at each other, our attention quite engaged, and flinched through that fraction of a second of waiting to see if it stopped or got worse. It stopped.

Our sport is guessing whether a temblor is small and nearby or large and distant. This was certainly the loudest one I can remember but it left nothing swaying, so I guessed it was a pip-squeak magnitude 2 directly underfoot. My wife was more impressed and guessed a magnitude 4 farther away. The U.S. Geological Survey has a nice website that within 10 minutes told us it was a magnitude 3 whose epicenter was four miles beneath a high school less than a mile from our house. We called that one a tie.

Magnitude 3 is nothing, a trifle. My personal best was of course the magnitude 7 Loma Prieta quake of 1989, which knocked a section out of the Oakland Bay Bridge and interrupted the Giants vs. A's World Series. I was working as a supervisor in an environmental chemistry lab at 5:04 p.m. on October 17 when the earth broke 110 miles away. I suddenly felt dizzy and thought it was just me until I saw everyone else reeling, too. Now, the official advice is to stay indoors and ride it out under a sturdy piece of furniture; in 1906, a lot of people were killed when they ran outdoors and got clocked by falling debris. All I know is that everyone in the lab simultaneously realized they did not want to be inside a concrete slab building filled with hazardous and flammable chemicals and gases if it decided to come down. I got behind my co-worker Ken, who is about 6-foot-7 and 250 pounds, and followed him out like a running back on the heels of a blocker. Out in the parking lot I saw the most amazing sight: asphalt rippling like waves on the ocean, with parked cars bobbing up and down like boats. It was, frankly, both deeply disturbing and really cool.

(I imagine my friend Sherwood, whose home I reckon was right on top of the Loma Prieta epicenter, has a much scarier story to tell, assuming he was in the area at the time.)

There's a kind of irrational, fatalistic insouciance that goes with living in Earthquake Country. I think you either get used to the idea that the world can shake itself to bits at any second or you move away. I have a friend who grew up near my neighborhood back when it was a plum orchard and remembers how the neat ranks of trees were split and offset by the faultline that ran through them. I always laugh when I tell people that, although it's not really funny. But the fact is that, although some locations are better than others--bedrock beats alluvial plain--almost nowhere on the West Coast is safe.

I don't believe in fate but I do trust probabilities and statistics. Big quakes happen on scales of decades to centuries, while major quakes (like 1906) happen on scales of centuries to millenia. Modern building codes give me some confidence that my wood-frame home will survive anything short of total disaster. We take the prescribed precautions. All in all, I'll be here a relatively short time (geologically speaking) and like my odds better than if I resided in Tornado or Hurricane Alley. For us, living here is worth the risk. Still, it's interesting to get a little kick in the pants once in a while. Makes you think.

My Little Earthquake, all over in
about half a second (courtesy USGS)
.

3 comments:

R said...

...it's like my geology class...

Well...what I was told was there's about 26% chance that in the next 30 years an earthquake of M6 (I think) or bigger will happen on the Hayward fault (a.k.a. Rodger's creek fault, ya know, the one that runs right under our house) and there's a 30%-70% chance of a M7.9 quake on the southern part of the San Andreas fault system within 30 years. I've never heard of a really loud quake before, without much ground motion...it sounds like something underground exploded! I should send my professor a link to this, he'd have a field day.

Sherwood Harrington said...

You keep on watching out for the earth moving under your feet; I'll keep tabs on whether or not the sky comes tumblin' down. That way, we've got it all covered.

Our sport is guessing whether a temblor is small and nearby or large and distant.
The way I play that game is to try to determine whether the p-waves (thumpitty-thumpitty) and the following s-waves (swaying motion)come right on top of each other or are noticeably separated. If the latter, then it's probably a pretty big one far off. If the former, then it's nearby. Of course, I'm usually too freaked out to be quite so analytical.

[Re Loma Prieta, 1989] I imagine my friend Sherwood, whose home I reckon was right on top of the Loma Prieta epicenter, has a much scarier story to tell, assuming he was in the area at the time.
I wasn't; I was in a scarier place (in retrospect): Oakland. I had just gotten my current job in Cupertino, and was still living in an apartment in the Adams' Point district near Lake Merritt. I was watching the pre-game show for the Series and, when the quake hit, I thought it wasn't much (the apartment building was anchored solidly to bedrock.) A few unwashed dishes cracked in the sink, but that was it. I heard a strange rumbling noise outside -- which I later learned was the Cypress Structure on the freeway collapsing, a noise I heard in nightmares for long after.

That night provided one of the most spectacular views of a dark, dark night sky I have ever seen, punctuated occasionally by the blue, distant flashes of exploding transformers.

But the fact is that, although some locations are better than others--bedrock beats alluvial plain--almost nowhere on the West Coast is safe.
Actually, places like Hollister (one of California's three self-proclaimed "earthquake capitals") is probably pretty safe precisely because of its frequent shakers, which continually release the stress along its part of the San Andreas rather than having it all blast out at once every century or so. But try telling that to some visored actuary in an insurance office in Iowa.

Brian Fies said...

...Yeah, but then you have to live in Hollister....

Sherwood, I knew you'd have a story. Thanks for sharing it. I know about the different feel of the p- and s-waves but also realize my sense of time is pretty distorted during an earthquake. Unless I have the presence of mind to actually watch a clock during one--usually when I'm more concerned about which sword of Damocles or pot rack is hanging over my head at the moment--I don't trust my judgment of concepts like "fast" or "slow." I know the Loma Prieta quake was a big one because I knew I could not have physically run from my lab to the parking lot in less than 20 seconds or so, and I still got out there to see the ground ripple; that's about the best I can do under the circumstances.

R, don't try to shake my rock-solid irrationality with facts. I thought I taught you better than that.