4 Answers

earthquakes have been going on for thousands of years.  however, science is showing man made activity can help trigger the earth to rock and roll.  which is not funny when you live in the San Francisco bay area, like I do. very scary.  I was in a building in downtown san Francisco, on battery street, when the 1989 earthquake broke out.  I was on my way the embarcadero one building to see my dentist on the 22 floor. when the building I was in, started shaking I thought we were all going to die. a friend of mine who worked on the 32 floor at kcbs radio told me some of them thought it was over too and that the office furniture all slid to one side of the room. no no fun. and somebody keeps building these high sky scrapers over earthquake faults. $$$ makes us do funny things.

....man and greed

It's been proved that fracking can cause minor "earthquakes", but Mother Earth has a way with her, hence your earlier question about climate change, these things happen naturally ( by which I mean BIG Earthquakes) and the climate changes every few million years or thereabouts, I wouldn't presume to tell someone who has lost their home through a fracking incident that it was Mother Natures fault, only that the company who were carrying out the fracking were negligent.

I reckon Tectonics might have a far greater role to play JH,have a look at this link,and check out the Tectonic Plates in America,hence the reason you guys may have more earthquakes than Aussie..>>>>>>>><<<<<<<..http://geology.com/plate-tectonics.shtml