An accidental discovery has brought scientists a step closer to predicting earthquakes. It came about as part of an unrelated effort to measure underground changes caused by shifts in barometric pressure. A team of researchers found that increases in subterranean pressure preceded earthquakes along California's San Andreas Fault by as much as 10 hours. The finding was determined by dropping a stereo-speaker into a hole bored along the fault line. Researchers transmitted pulse signals deep into the hole and found that waves slowed dramatically before two minor earthquakes over a two-month period in late 2005. A two-year study at the same seismically active location begins this September. This effort is only a preliminary step in trying to improve warning systems for earthquakes. The perfect warning system is still many years away according to scientists involved in the project.