Am I missing something or does the massive Chilean earthquake and it's aftershocks force a re-evaluation of the current theories of plate tectonics? The USGS reports all the quakes at a depth of about 21.7 miles, in front of, along and behind the fault line. This would suggest a slippage between the surface plates and whatever lies beneath them rather than a slippage between the two plates. Surely, if present theories are correct, the depth should have been greater the further east one travels. Or am I being remarkably thick?
You're forgetting that the pacific plate needs to bend under the south american plate, and that that bending, combined with the convergence between the plates generates stress in the earths crust at the surface for many kilometers in either direction. Also, you are correct, there is a trend in earth quake depths as one moves in the direction of plate motion. I can demonstrate this in the country that I live in (across the pacific pacific from Chile). Please Register or Log in to view the hidden image! Please Register or Log in to view the hidden image! Please Register or Log in to view the hidden image! In the northern part of the country, the pacific plate, on the right, subducts under the indo-australian plate, on the left. In the Southern Part of the country, the Indo australian plate on the left subducts under the pacific plate on the right (the change in direction is to do with the formations in Fiordland - the bottom left hand 'corner' of the country). The maps show that in the northern part of the country, the depth of the earth quakes increases as you move from right to left, and in the southern part of the country from left to right. I've left out those earthquakes of less than 40km depth, because they occur virtually everywhere. I hope that helps anyway.
