Wednesday, February 20, 2008

Subduction zones from the side

The USGS earthquake site is one of my favorite sites on the net. Maybe it's just that I'm a hopeless seismic rubber-necker. But maybe it's the wealth of information the USGS makes available.

Each major earthquake has its own set of pages, with tabs for general information and maps and scientific information. And lately, they've added a number of new types of scientific information. There are more beachball diagrams, both for current earthquakes and for historic earthquakes. (The southern California earthquakes have particularly detailed information from the Southern California Earthquake Center.)

And then, for some earthquakes, there are diagrams like this (from the Feb. 20, 2008 Mw 7.5 earthquake off of Sumatra):

Look! It's a subduction zone! Ok, yes, I knew that. But it's nice to see the earthquake foci in cross-sectional view. The subducting plate coming in from the left is nearly flat, until it reaches the islands of Nias and Simeulue, and then it heads down into the mantle. The big triangular area of orange and yellow dots probably represents the thrust faults in the accretionary wedge. (I wonder if the earthquakes near the surface on Sumatra are on the strike-slip fault that runs down the island, or if they are volcanic earthquakes? Does anyone know?)

There are black and white images like this, of Wadati-Benioff zones, in all sorts of textbooks. But it's nice to be able to see recent earthquakes plotted in this context.


Julian said...

Oh, whoa! For all I check the USGS earthquake site (a couple of times a day, speaking of rubbernecking), I've never noticed those cross sections before. Very very cool - thanks for pointing it out!

Kim said...

Julian, do you know about the earthquake notification service? It's great for rubber-necking.

Julian said...

I do know about the ENS - its email about the 6-pointer in Nevada was the first thing I read this morning. That kind of news certainly makes one wake up fast!