I'm told we had a moderate earthquake here last night. Indeed, it is reportedly the largest earthquake in the area since the 1989 Loma Prieta quake -- which, as it happens, was the temblor that welcomed me to the San Francisco Bay Area.
I completely missed it.
You see, I was driving home from the store with the carrot sticks for the younger Free-Ride offspring's classroom Hallowe'en celebration. The roads haven't been repaved in a while, so I suppose the jostling that I attributed to the road surface might have been caused in part by seismic activity.
At home, the sprogs felt the shaking (although at first they thought that my better-half might have been causing it). Dozens of miles away, Uncle Fishy felt it (and called to see if we had felt it, too). A bunch of people stopped what they were doing to report their experience of the quake to the USGS.
But it's hard not to wonder how much our perceptions of these seismic events are colored by our prior experience. Looking at the estimated severity of the quake reported by folks much further from the epicenter, we asked each other, "Do we tend to underestimate how long or how violently things shake?" We've lived in earthquake country a long time, and we know that most of the shaking just lets out some stress. Generally, there's not any damage. At Casa Free-Ride, nary a book fell from a shelf. At my office, I noticed a few items on my desk that must have fallen from my shelves -- a framed picture, a stack of Post-It notes, a container of red pepper flakes from the pizza joint -- but it was hardly a disaster scene.
Which means we'll probably continue to be pretty nonchalant about the faultlines crisscrossing our region, even though the Hayward fault is averaging a major earthquake every 140 years, and we just passed the 139th anniversary of the last one.
Undoubtedly, part of our nonchalance has to do with the fact that seismic retrofitting became a serious issue after the 1989 quake, and that earthquakes are so much a part of the standing conditions in these parts that construction has assumed they would happen. Our houses, by and large, are built to ride out the rumblings.
But part of it probably has to do with the fact that it's really hard to predict earthquakes in the same way you predict rainstorms, or even firestorms. Despite what people might tell you (on the basis of a couple memorable quakes), there is no such thing as "earthquake weather". You don't get a tip-off in the five-day forecast.
They hit, and then they stop. The shaking itself seldom lasts more than a minute.
There's something about this state of affairs that leaves me feeling almost negligent. I'm taking for granted that for the most part temblors won't cause major disruptions in our lives, and that in the cases that they might, there's not a heck of a lot we could do to prevent them.
A really big earthquake could wipe that complacence right off my face. But short of leaving the area, I'm not sure what a reasonable person should do in the light of the knowledge that a really big earthquake will, eventually, happen here.
I heard it on the local radio here in NC.
It spooked my cats. The thing that worries me is the spot in Southern California where we have 7-10m of continental drift to catch up on...
This was probably the strongest earthquake I've ever felt up here in Berkeley, and it lasted longer than most of the others too.
I also thought those newspaper headlines about "139 years since the last big earthquake, and it goes every 140 years" were pretty bad (though I didn't read the article). They didn't give anything about the statistics about distribution of earthquakes, just average time between them. Those facts are consistent with it being a Poisson process, in which case at any moment the expected wait to the next earthquake is 140 years, no matter how long it's been since the last one. Or some sort of process where the wait between earthquakes is normally distributed, with mean 140, in which case maybe there is something to be worried about. I suspect the Poisson process is more likely, but maybe I'm wrong.
I had barking dogs and fleeing cats, but nothing fell from a shelf. It's strange how time seems to crawl when it's happening, though. I was starting to think about ducking in to a doorway when it stopped.
I felt a bit of shaking here in San Francisco. Having lived in earthquake country all my life, I too tend to be complacent. You can't predict when the next big one will be; you only know that it will happen sometime. The best you can do is earthquake proof your house, have good insurance coverage, have an emergency preparedness kit, and evacuation plan.
Carrot sticks for a Halloween celebration?!?
I understand passing on healthy eating habits, but I am still far, far away from celebrating anything with... carrot sticks!
Your description sounds consistent with that shake map - the maximum intensity on the map is VI, and drivers don't feel earthquakes below intensity VII. (Actually, your description is perfect for Mercalli intensity V.
The latest thinking on how one earthquake affects other earthquakes would predict that this latest quake would make the Hayward Fault in most of the Bay Area more stable. It's a pretty new approach, though, and every time there's an earthquake there's something new to learn.