Understanding what happens at the epicenter of an earthquake, as the tectonic plates beneath the earth shift and the earth shakes, could help better predict when and where the next big one will hit. For the past six years scientists from a number of institutions have joined in a project called San Andreas Fault Observatory at Depth, or SAFOD. They have drilled to the core of the San Andreas Fault, near Parkfield California, down to a specific area along the fault known to experience a number of small earthquakes every year. By retrieving and studying core rock samples from that site, geologists Chris Marone and Brett Carpenter and hydrogeologist Demian Saffer are getting a better understanding of the types of rocks involved in major quakes, versus the rocks present at more forgiving ones.