One hundred years ago today, 18 April 1906, a major earthquake (estimated to be 7.9 on the richter scale) nearly destroyed the city of San Francisco and did some serious damage to other communities in the area. Here in the Bay Area, there are various commemorations of the event taking place, and the local papers have all hit the vaults to dig up accounts of the quake, and of the fires that followed. (See, for example, the Chronicle’s “Great Quake” page. Of course, the U.S. Geological Survey has a page with great quake links, too.)
So in a very obvious way, you could say there’s lots of earthquake “awareness” in these parts. But the commemoration (some even call it a “celebration”, although no one is actually celebrating the destruction and deaths caused by the quake) has an uneasy feel to it.
We know a lot more about earthquakes than they did in 1906 — and here, by “we” I mean both scientists and lay people. (You can look at this very nice GSA Today article about how our understanding has improved. Or, check out this set of ten short articles from USGS targeted at students, teachers, and parents.) Plate tectonics, man; the plates are in motion, there’s friction, stress builds up and needs to be released. You can work it out a little at a time (perhaps with frequent, smallish earthquakes). Or, after a period of relative quiescence something big can happen.
Those of us who live in the Bay Area know that there are faultlines running through our whole lives — home, school, work, recreational areas, the roads and transit routes that connect them all (’cause everyone commutes here). We know that stress is building up along each of the major faults, and that eventually something will have to give. Maybe a few times a year we feel a rumble and we go online to see if it was a quake or just a big truck driving by. Some of us find the little temblors reassuring — there goes a little of the stress.
But, they could just be the prelude to The Big One.
And, the geologists tell us, the probability of a major quake (magnitude 7 or more) in the next few decades is better than 50%. It’s not a matter of if, but when.
Yet hardly any of us have real earthquake kits, or plans for dealing with the aftermath of a major quake.
It’s not because we think the geoscientists can prevent a quake. Nor, I think, is it because we have total faith in all the seismic retrofitting that has been undertaken since the Loma Prieta quake (a 6.9) in 1989.
I think it may come down to the probabilistic nature of our knowledge here.
Geologists aren’t in a position to say, “We’re expecting a quake along the Hayward fault, with this approximate epicenter, in the 6.8 to 7.3 range, in May of 2006; take appropriate precautions.” A month is a ridiculously small window of time, geologically speaking. Even if it weren’t, how high a probability of seismic activity would there have to be before you could announce that something is going to happen? Greater than 0.5, surely, and probably less than 1.0 … but where’s the cut-off? And, given that improbable stuff actually happens (and probable stuff sometimes fails to happen), how do you avoid becoming the earthquake predicting agency that cried wolf? (“Well, they said all hell was going to break loose on that fault, and we battened down, and not a darned thing happened. Alarmist scientists!”)
David Hume’s problem of induction just doesn’t bother most folks. The ground stood still yesterday. The ground stood still today. No good reason to plan on the ground not standing still tomorrow.
Maybe the risk of earthquakes would feel more real to us, and have more of an effect on our planning, if we could feel the seismic storm gathering like a thunderstorm or a blizzard. Right after the Loma Prieta quake, and then after the largish aftershock we had about 6 months later, people talked about “earthquake weather”, but I’ve felt that same “unseasonable” weather dozens of times in the 16 years since with no shaking associated. Unless you’ve got instruments in the ground monitoring the stress along the faults, you’ve got nothing to go on. From the individual’s point of view, it might as well be 1906. The Big One is going to surprise you.
And maybe this is just how things are. Maybe we expected science to turn the whole world into something completely predictable, whose trajectory we can compute accurately to many decimal places given sufficiently precise information about where things are right now. But maybe the best science can do, at least in certain realms, is tell us what forces are at work, and what outcomes are most probable, and we’ll just have to wait and see which of the possibilities become actualities. Maybe we’ll be in a position to understand quite a lot, but not always in a position to predict precisely what’s going to happen at any given moment.
Probably, embracing the limits of our science shouldn’t put us off from assembling emergency supplies. Really, I should do that soon. But what are the odds that the next Big One would strike at such a perfect interval from the last Big One?