The movement attributed to the earthquake is less than an inch along the surface of the fault and would be practically undetectable to the average resident. But this intrigued the researchers for two reasons. "They don't know what that means, and they've never seen this particular course of error," said Zahari Ross, an associate professor of geophysics at Kaltech and the author of a study of error published Friday in the journal Science.
Caltech and NASA researchers recognize the change in error as creeping. However, this phenomenon usually happens without an earthquake, according to the US Geological Survey.
The results come as scientists continue to warn that the "Great" ̵
1; a monstrous earthquake that could potentially flatten Southern California – is overdue.
It started on July 4, when a 6-degree frontal impact struck southern California, the study said. This gave way 36 hours later to a major shock of 7.1 magnitude, which sent concerns to Arizona and Nevada. The low population density in the area has saved it from significant damage, although nearby naval facilities require billions of dollars to repair.
The main impact was broken only by kilometers from the Garlock Fault, a major fault line that runs more than 180 miles from the San Andreas Fault to the Death Valley. It has remained relatively dormant so far and has slipped 2 inches after the July quakes, researchers have found.
Combining advanced seismometer data with satellite image of fault breaks, the team monitors more than 110,000 aftershocks in the surrounding area for 21 days. Researchers say the "domino-like sequence of tears" is a heavy burden on Garlock's mistake.
Southern California has seen several triggered crawls before, he said. The southern end of the San Andreas Fault began to creep after a 7.2 magnitude earthquake just south of the US-Mexico border. Then the creep did not cause a significant earthquake.
What does all this mean for the Big One?
Californians have long been afraid of the Big One. But the study proves how much is not yet known about earthquakes and how difficult it is to predict.
The USGS says that there is a 31% probability of a magnitude 7.5 earthquake to hit Los Angeles sometime in the next 30 years. According to LA County, the county is home to more than 10 million people.
The South San Andreas Fracture typically observes massive earthquakes every 150 years. The latter occurred there in 1857, which means that the segment is considered to be a "likely earthquake site".
But the earthquake of magnitude 7.9 in San Francisco in 1906 means that there is a slightly less chance of a major earthquake in the northern segment of the fault.
Seismologist Lucy Jones tweets
that there is a 2% chance of the Big one appearing every year and a chance of 1 in 20,000 every day.
The "Great" is impossible to predict. So the USGS is urging California residents to prepare, refurbish homes to make sure they support during an earthquake, and to maintain a healthy supply of food, water and fuel in an emergency.
Dakin Andone of CNN contributed to this report.