March 21, 2011

Unwarranted alarmism, and a hiatus for field work

Posted by Austin Elliott

There have been plenty of doomsday claims circulating the internet in the wake of the massive 9.0 “Tohoku” earthquake–lots about supermoons, some about dead fish, some merely about some alleged “pattern” of recent quakes circling the Pacific, a pattern generally conveniently selected to only include earthquakes that have hit the news. I won’t bother to give any of these claims too much credence by linking to them here, but they’re easy enough to come by.

Fortunately there are some scientifically grounded explanations as well, like this editorial by USGS seismologist Susan Hough.

The bottom line with claims about patterns of earthquakes and predictions for the near future is that for them to be of any value, they have to predict quakes better than random chance. In other words, it’s easy to “predict” that there will be a significant earthquake on the U.S. west coast–we have earthquakes here commonly! A prediction needs to be precise in space, time, and magnitude to be of any value beyond the forecasts we have developed already to understand earthquake hazard.

It is essential to be critical when you hear predictions that concern matters of such importance as whether you will be hit soon by a devastating earthquake. Two helpful guidelines to keep in mind are

1) If you live in a quake-prone area, you’ve had a pretty high risk of such earthquakes all along–is the prediction precise enough to make a difference in your preparation?

2) As Susan Hough points out, very few predictions precede large earthquakes, but plenty of large earthquakes precede predictions. Renewed awareness of quakes inspired by a devastating event tends to foster the anxiety that faux-predictions thrive on.

In that second vein, it’s important to remember how many earthquakes are going on around the world all the time. Most of the largest ones occur far out to sea, deep beneath the ocean’s surface. There’s nothing special at all about Christchurch’s 6.3 except that it hit directly below a city. There are scores of others like it every month. Don’t be fooled by “connections” like that; in fact it’s valuable to check the USGS’s “significant earthquakes” page for reminders of just how many large and/or devastating events have occurred within recent memory.

Other than that little spiel, there’s plenty I’d like to pass on regarding the information and news pouring forth from Japan, but I have limited time as I prepare for two weeks of field work in Mexico. Some other bloggers are doing a great job compiling information, and their posts are well worth mining for informative tidbits about the quake. Notably, the Shaking Earth has a collection of resources, and Chris Rowan at Highly Allochthonous posted an earthquake round-up with links galore.

There are some neat–if somewhat disconcerting–liquefaction videos coming out of Japan, but I’ll devote a later post to discussion of these.

I’m off to the borderland of northern Baja, Mexico for two weeks, to re-survey the escarpment left by surface rupture of the 7.2 earthquake there last Easter day (pictured in the banner of this blog). I’ll come back with pretty pictures and info about that fascinating rupture.

Myself and fellow UCD grad student Peter Gold surveying the fresh April 4, 2010 El Mayor-Cucapah earthquake rupture with a terrestrial LiDAR scanner last spring.