in my unqualified opinion, i think you will find that if you had a graph of all the seismic activity for the last 200 years, you would see sharp raises and falls. but i think if you look at a graph over the entire history of the earth it would be quite steady.
i have heard people claim that it must be all the polution and that man is doing it somehow, and while that is a possibility i am yet to see any evidence to back up the claim. i think mankind is having an effect on the climate, there is evidence to support that. i just dont think we have anything to do with the earthquakes. at least not until i see some evidence or at least hear the personal opinion of someone who works in that field.