Sunday, August 9, 2009
July SRL - Crustal Tomography
I just love this stuff! Every few years they gather up all the data from seismometers all over North America, and calculate the velocities directly under each seismometer. They do this with the signals of the earthquakes in the upper figure. The final picture can be also considered as the temperature of the crust at various depth slices.
Looking at the bottom figure, we see a big hunk of the crust is relatively cold. This is most likely the original craton, with cold, deep roots. As I have said before, the continents are made of the floating fuzz of silicon dioxide, which has come out of the rest of the molten rock, much like the head on a beer. Over the many tectonic cycles, this stuff has been squooshed together.
Note Ontario, it's not that cold and old. I find the pattern quite interesting, and wonder about it. If this is true, then it has some implications for seismic hazard.