Sunday, March 30, 2014

The BIG ONE is COMING! Well, yeah, but...

The San Andreas fault in the San Francisco Bay area. The two reservoirs are Crystal Springs and San Andreas, which gave California's most important fault its name. Photo by Geotripper.

It seems like there has been a bit of shaking going on in California over the last few weeks. There was the 6.9 quake off the coast of Eureka on March 9, a 4.4 magnitude tremor in the San Fernando Valley on the 17th, and now the 5.1 magnitude quake in La Habra. It's enough to make people paranoid about quakes in general, and the BIG ONE in particular. Are these precursors to the BIG ONE? Are they relieving some of the stress that will prevent the BIG ONE from being so bad? We love to talk about the BIG ONE, and if the media outlets have their way, we will worry and fret about it, enough so as to tune in to their stations for more scary updates (to keep those ratings afloat). I've rarely been impressed by media coverage of earthquakes, and this week has been no exception. I've heard through tweets that some media outlets trumpeted official statements warning of bigger quakes to come in 24 hours while conveniently forgetting to mention the "5% chance of" statement that preceded the word "bigger".

Of course, in some ways it's worse. We're not waiting for the BIG ONE in California. We are waiting for the BIG ONES. The San Andreas fault gets lots of attention, but there are numerous active fault zones in California, and the San Andreas itself behaves like four independent fault systems. There was the devastating earthquake near San Francisco in 1906 that garners much attention, but there was an equally large quake near Fort Tejon in Southern California in 1857, and the Salton Sea region was shaken around 350 years ago. These different segments of the San Andreas seem to move every century or so. A huge quake shook the eastern Sierra Nevada in 1872, killing a tenth of the population in the Owens Valley (28 people). Each of these quakes were in the range of magnitude 7.7-7.9, although some estimates range as high as magnitude 8. Add to this list the 1952 Tehachapi quake (7.3-7.6), the Landers quake of 1992 (7.3-7.5), the Hector quake of 1999 (7.1), the El Mayor quake of 2010 (7.2, just over the border in Baja), and the Cascadia Subduction Zone quake of 1700 that no doubt affected the northernmost part of the state. It was very likely a magnitude 9 event.

I should mention that I successfully predicted these quakes. We discussed earthquakes and the "art" of earthquake prediction in my classes two weeks ago. We pointed out that psychics predict earthquakes all the time, and that they are never wrong (how wrong can you be when you say "I see a major city being devastated by an earthquake this year" without specifying a day or location?). To prove the point, I predicted that a quake would happen in northern California within a few days, and that another would happen in the south state as well. I make this prediction every semester, and I am rarely wrong. All such predictions are crap, of course, and do no one any good.

No one can predict earthquakes, and anyone who says they can is lying or is deluded. But we can predict where they will happen, and we can determine the probability that they will take place within a certain time frame, usually 30 years. This is the nature of the maps that I am posting here from the U.S. Geological Survey, the Southern California Earthquake Center, and the California Geological Survey. Such maps are a most useful tool for educating the public about where the greatest seismic risks are located in the state (note how distressingly close they are to the most populated parts). There is a lot more to the tectonic framework of our state than just the San Andreas fault!

It is interesting to me that since these probability maps came out in 2007, we've already had a 6.9 quake in northern California, and if you count just over the border, we've had our predicted magnitude 7 quake in 2010. It is important to note that neither of these events had any particular effect on the stress levels that have built up on faults like the San Andreas, Hayward and San Jacinto. They are still just as likely to shake in the next 25 years or so. What do we take from this? The quakes are coming, and we need to be prepared for them (start here: Everyone who lives in California should have emergency supplies of water and food. Even if you live outside the high risk parts of the state, you will still be affected, as the energy grid will be damaged and emergency services we take for granted will be headed into the areas where damage is the worst.

Do these kinds of disasters make you rethink the idea of living in California? You could move to Kansas and put up with tornadoes. You could go to Nebraska and enjoy the Polar Vortex. You could go to Louisiana or Florida and deal with oil spills and hurricanes. You could move to Oregon or Washington and deal with volcanic eruptions. There really is no place that is free of natural disasters, and the processes that cause them may sometimes have the benefit of producing beautiful scenery and interesting geological outcrops. I'll pick California every time.


Gaythia said...

Hey, we in the Pacific Northwest enjoy a considerable earthquake threat in addition to our volcanic eruptions:

Garry Hayes said...

Oh, indeed you do! I didn't want to pour it on with the hazards up there. Lots of landslides too, as this week's tragedy shows. But a wonderful place to live, otherwise!