here's an interesting site given the recent news of the Ecuadorian and Japanese earthquakes especially if one is inclined to believe this rock we inhabit is a static ball game. This rock is in constant motion...land masses bing bonging into and off each other...oceanic plates being formed and ridden over by continental plates
all give rise to the near constant grinding and shaking we call earthquakes.
check out the link below to get an idea of the quantity...they only make news if they're big or in a highly populated are.