Hi Chris. For some reason I can’t open any of the links to world quakes. If I remember correctly the quake in Russia was below 300Km as well as the quake in Bolivia. I don’t think the quake in Japan meets the criteria for a deep quake. However I do know the “moment tensor solution” shows it to be a pure thrust quake.

There is however a partial answer as to why it is possible for quakes to occur where they shouldn’t. Take Care…Don in creepy town

First it is important to note that almost 30% of all earthquakes occurs at depths exceeding 70 kilometers and only 8% happen at depths greater than 300 kilometers. At these depths the pressure in the mantle is from 3 to 10 gigapascals, which is thousands and thousands of times more than the sea level pressure. This extreme pressure causes the hot melted mantle rocks to flow (exactly like volcano lava) at a very slow rate and consequently the stress produced is by far less than what is needed to cause earthquakes such as the ones along faults or trenches. Nevertheless, deep earthquakes occur. Because the frequency of earthquakes steadily declines down to about 300 kilometers, most geophysicist believe that the events originating between 70 and 300 kilometers below the surface are due to the plate tectonic and friction mechanism occurring on the earth’s crust and upper mantle. Deep earthquakes ( below 300 km ) however, follow an entirely different pattern, so they must be caused by a separate mechanism.

• Deep Earthquakes