Wednesday, May 02, 2012

A Footnote on 'The Big One'


No sooner had I written (last month) my blog about being physically (and spiritually) prepared for a major earthquake, when I experienced one ... on the San Andreas Fault, no less! (Or at least close to it.)

My inlaws live in Wrightwood, a town divided by the San Andreas faultline, in the mountains an hour's drive northeast of the Los Angeles basin. We visited them last weekend. Saturday morning, shortly after 8, we were taking our time getting around ... my wife had just started a shower, and I was lazily lying on my back in bed, eyes open, thinking about the weekend and enjoying the relative quiet ...

A Google map of the eastern half of the town of Wright-
wood. The red line is the San Andreas fault. The yellow
arrow points to where I was lying in bed during Saturday's
quake. The magenta arrow points to a home my wife and I
nearly purchased around 1990, before we discovered it
was literally sitting on top of the fault itself.
... when that quiet was suddenly interrupted by a sharp horizontal jolt, accompanied by the rattle of various things disturbed around the house, and followed by a strange but diminishing vibration. It lasted all of about five seconds. Wow, I thought, suddenly very awake. That had to be an earthquake! And there we were, two short blocks (about 700 feet to the north) from the renowned San Andreas Fault itself.

My second thought was, What if that was a foreshock? I realized I didn't want to go through whatever might be ahead without my contacts on (I'm legally blind without them), and also I should warn my wife ... for who really wants to be in the shower when the Big One hits?

So I rushed breathlessly into the bathroom and asked her if she'd felt it. "Felt what?" she said, fairly alarmed by my sudden entrance. I told her I had just been jolted out of bed by what I estimated to be about a 4.0 shaker. "Nope, didn't feel a thing in here," she said. "But you'd better go check on my parents."

Fred was sitting in his usual chair, reading the paper. He was oblivious. Dottie was puttering around in the kitchen, and she hadn't felt it either. I think both thought I might be a little crazy. So I turned on the news and was vindicated. The moment it came on they were announcing that a 4.1 quake had struck, fairly shallow near the town of Devore (just 12 or 13 miles southeast of Wrightwood). (The San Andreas Fault also runs through Devore, though the epicenter of this quake itself was about a kilometer south of the fault line, and 13.5 kilometers deep, according to the USGS.)

So I felt pretty good about my casual 4.0 estimate. (The USGS later downgraded the magnitude to 3.8.)

Of course it turns out it wasn't exactly a foreshock to the Big One, just another small bump along the long, slow road to catastrophe. Some day the Big One will surely come to the San Andreas Fault (the last time it did was in 1906, the big San Francisco 7.9 quake), just as it will come to the Cascadia Subduction Zone (the last time there, on January 26, 1700). But, hopefully, not within our lifetimes!

Actually, technically, that chance is about 1 in 5, depending on your age. The USGS-associated "2003 Working Group for California Earthquake Probability" assigned "a 21% probability that the San Andreas Fault would produce a magnitude 6.7 or larger earthquake in the next 30 years."

Regarding the Cascadia subduction zone, the government of Canada says geological evidence shows that 13 "megaquakes" have occurred along the Cascadia fault during the past 6,000 years. That's approximately one every 462 years. The last one (a 9.0) occurred 312 years ago, rupturing the fault for a distance of 1,000 miles and causing massive devastation both throughout the Northwest, as well as wiping out fishing villages in Japan in the resulting tsunamis.

What would have happened Saturday morning had the Big One (say, 8.0 to 9.0) struck the San Andreas Fault in Southern California, with me, lying in bed a scant quarter mile away from the slip. Hard to say, for sure. Many older homes in Wrightwood (some made out of stone) would surely be destroyed. Fred and Dottie's is newer, and quite well-built, so it might have survived, but surely would have sustained a lot of damage. I have no doubt we would be isolated in this dry mountainous town by landslides, and possibly faced with the threat of fire. My inlaws stock a lot of food, they're notorious for that; but water might be a problem. Any injuries would be difficult to deal with, with help potentially unavailable; they are both 92. Fortunately my wife is an R.N.

In a town like Wrightwood, population of several thousand, I have a feeling we would be spending a lot of time with picks and shovels, trying to dig people out of the rubble. It would be interesting, that's for sure.

In my role with World Vision, I've seen the aftermath of some major quakes. It's hard to predict who will survive, though the poor generally have a much rougher go of it. When you live on the margins, and you're just trying to survive a normal day, there isn't much thought or room for preparation for a possible catastrophe.

But the rest of us, of course, don't have that excuse. We should be get prepared!


covnitkepr1 said...

I was in Fairbanks Alaska during the big one up there...not much fun.

I write and maintain a blog which I have entitled “Accordingtothebook” and I’d like to invite you to follow it. I didn’t see a follow widget on this site, but if you put one up...I will gladly follow you publicly as well.

Larry Short said...

Yes, I've read about the great Alaska quake! That must have been something. What kind of impact did that have on you and your family?

Larry Short said...

Thanks, @covnitkepr1, I've gone in now and added a few of the newer widgets to the rightnav! (I hadn't tinkered with that for awhile. Lots of new tools out there.) Including several "follow" widgets. Appreciate the heads up!