California earthquakes just caused a major fault line to move for the first time, a study shows
The movement attributed to the quake is less than an inch along the surface of the fault and would be virtually undetectable to an ordinary resident. But it has intrigued researchers for two reasons. They're not clear what it means, and they've never seen this particular fault move, said Zachary Ross, assistant professor of geophysics at Caltech and an author of a study of the fault published Friday in the journal Science.Researchers from Caltech and NASA recognize the fault shift ascreeping. The phenomenon, though, usually occurs without an earthquake, according to the US Geological Survey. The findings come as scientists continue to warn that the "Big One" — the monstrous earthquake that could potentially level populous Southern California — is overdue.
Remember the July earthquakes? There were 110,000 aftershocks
It started on July 4, when a 6.4-magnitude foreshock struck Southern California, the study said. That gave way 36 hours later to a 7.1-magnitude main shock, sending tremors as far as Arizona and Nevada. The area's low population density saved it from substantial damage, though nearby naval facilities require billions of dollars to repair. The main shock ruptured just miles from the Garlock fault, a major fault line that runs more than 180 miles from the San Andreas Fault to Death Valley. It has remained relatively dormant until now and has slipped 2 centimeters since the July quakes, researchers found. Combining advanced seismometer data with satellite imaging of fault ruptures, the team tracked more than 110,000 aftershocks in the surrounding area over 21 days. The "dominoes-like sequence of ruptures" put heavy strain on the Garlock fault, researchers said. Southern California has seen a few triggered creeps before, he said. The southern end of the San Andreas fault started creeping after the 7.2-magnitude earthquake in 2010 just south of the US-Mexico border. The creeping then didn't lead to a significant earthquake.