The trouble with big earthquakes is that their subterranean root systems can lurk for centuries or millennia before building enough energy to explode. Among many places, this is true of the New York City area, where scientists believe big quakes are possible—but probably so rare, it is hard to say exactly how often they come, or how big they could be.
Click here for original story, Balancing act: Can precariously perched boulders signal long-term earthquake risk?
Source: Phys.org