Wednesday, April 23, 2008

Dear NPR: let's talk earthquakes

NPR's Bryant Park Project features a story about last week's M 5.4 earthquake in Illinois. And, well, they should have interviewed Maria instead, because her post explaining earthquakes in Illinois is really good. And NPR's story, ummm, isn't.

What did NPR get right? Well, yes, there have been big earthquakes on the New Madrid seismic zone. Really big earthquakes. And the 1811-1812 quakes (which supposedly rang church bells in Boston) are worth telling people about.

But...

The California activity — along what is known as the San Andreas fault — is a result of the North American plate riding over the Pacific plates and continually building stress, Gibson says. The New Madrid fault, on the other hand, is an "ancient scar" where two very old plates are slowly pulling apart.


Ok. Problem #1: California. California is on a strike-slip plate boundary (as Julian's photos show very nicely). The Pacific plate slides past the North American plate. Mostly. Except where the boundary isn't oriented in quite the right direction. But it's not a subduction zone, as implied by "riding over." (You need to go north, near the Oregon border, to find one of those. And up there, North America slides over the teeny-tiny Juan de Fuca plate, not the Pacific plate.)

Problem #2: New Madrid as an active rift? The failed rift that is now the New Madrid seismic zone tried to tear North America apart 700 million years ago. It's not an active rift now. It failed. No ocean basin. No separate continents. Just lingering effects like low elevations and lots of old faults, just waiting to be reactivated. Maria's analogy is perfect: they are old injuries that react to unrelated events. In this case, I would guess that the fault was driven by some east-west compression of the North American plate, between the Mid-Atlantic ridge on the east and the San Andreas fault on the west. (The focal mechanism says that the earthquake involved strike-slip motion with east-west compression - consistent with reactivation, but not with active rifting.)

So. Seismic hazard? Yes. (And so are many other areas with old normal faults: one of the other big earthquakes of the 1800's was in Charleston, South Carolina.) Future beach-front property? Not without a lot of sea-level rise.

And should we care? Well, if the New Madrid seismic zone were actively building stress, we might have a better handle on the risks there. We could use continuous GPS to monitor the ground deformation. We could make a decent guess about the likely size of future ruptures, and the size of future earthquakes. And then it might be possible to decide just how crucial it would be to retrofit old buildings. But as it is, we've mostly got history, rather than theory, as a guide. And in most places, human history is too short to give a good feel for earthquake risk.

8 comments:

Fault Rocks said...

That reminds me of the time I heard Simon Winchester on my local NPR station, promoting his book on the 1906 earthquake. He made so many blatantly false statements I felt like throwing rocks at the radio. I called the station to find that the interview was pre-recorded and nothing could be done.

Tuff Cookie said...

Have you tried getting in contact with the NPR people? As annoying as it is to hear them make these mistakes - and as fun as it is to snark about them - NPR will never find out they're wrong unless people like us tell them. (Callan seems to have had some success fixing the lousy job some reporter did with his interview, so maybe there's hope.)

Julia said...

*groan* I wish the media could find a better balance between putting scientific principles into laymen's terms and oversimplifying it to the point of making it just plain wrong.

Kim said...

Tuff - Yes, I did think about contacting them (and I still may). However, the letters that are read on the radio need to be short, and it will take some work to pick the nits and explain why anyone would care in four sentences or less. (Also, blog posts can contain links to things like Maria's great explanation or to the USGS site. And they're around for people to stumble across in the future. Letters read on the radio are ephemeral.)

Julian said...

If I were to write to them, I'd hope more that the letter would be read by the various programming/writer types, who would keep the need for scientific accuracy in mind for the next show. I wouldn't personally be so concerned with having the thing actually read over the airwaves, but that may be just me.

But anyway. I'm glad you like the photos! I took gajillions more on that trip and am trying to think of a good way to format them on the internet.

Anonymous said...

Look, didn't you read the JIRR paper on this? The New Madrid fault is clearly the result of the collective weight of National Geographics cracking the continent in its middle. There is a crushing preposterousness of opinion in the scientific community on this subject.

Kim said...

But, anonymous, any earthquakes resulting from excessive weight above should have focal mechanisms consistent with a vertical maximum compressive stress! Geez, the things that make it through peer review these days.

;) ;) ;)

Kim said...

BTW - I did e-mail them. I wasn't nearly concise enough, I'm afraid, but I did e-mail them.