Risk of Earthquake on Major California Fault 5 Times Higher Than Normal

October 27, 2019 Updated: October 27, 2019

The 160-mile Garlock fault in California has begun moving for the first time on record and is now at a higher risk of rupture, local geophysicists say.

The fault is the second-longest in California, stretching from the edge of Ventura County in the west to the southern border of Death Valley National Park in the eastern part of the state. It’s capable of producing an 8.0 magnitude earthquake, according to a recent study.

The Oct. 17 study, published in the journal Science, found the fault’s movement was a result of this year’s Ridgecrest series of earthquakes in July, which destabilized nearby faults.

“We estimate that right now, the chances of a rupture on the Garlock fault are about five times what they typically are, and that is going to slowly decay back to its original level in the next few years,” U.S. Geological Survey research geophysicist Morgan Page told The Epoch Times.

However, Page said that the odds are still low that a substantial earthquake would happen along the fault.

“Typically, the hazard of the Garlock fault [is] about a 3 percent chance over 30 years for that central portion of the fault, so it’s not terribly high, and now it’s a little bit higher than that,” she said.

The Caltech team that conducted the study, along with NASA’s Jet Propulsion Laboratory, looked at images acquired by radar satellites from before and after the main Ridgecrest earthquake’s magnitude 7.1 shock. The team then used the two images to compare how the ground had moved.

“We were able to see that the Garlock fault, which is very close to the fault that ruptured during the Ridgecrest sequence, started to creep, which means that the two sides of the fault started to slide relative to each other,” Zachary Ross, an assistant professor of geophysics at Caltech, told The Epoch Times.

The creep isn’t limited to one section of the fault but a number of smaller sections along stretches of the fault. It has produced a number of small earthquakes recently in nearby areas, including Owens Lake and Panamint Valley.

“This is not just a single point on the fault. A whole segment of the fault is probably tens of kilometers. That whole segment all shifted,” he said. “We have seen this happen before on some faults in California, in particular, San Andreas, but never on the Garlock fault.”

Ross said that the probability of an 8.0 magnitude earthquake would be a worst-case scenario, and it’s unlikely that there will be a large earthquake.

“It’s not clear what this means. Most likely, it’s probably just going to go away on its own. It’s unlikely to lead to a large event,” he said.

The Ridgecrest earthquakes on July 4 and 5 had three main shocks of magnitudes 6.4, 5.4, and 7.1. The latter shock was considered to be Southern California’s most powerful earthquake in at least 20 years.

Effects were felt across Southern California, parts of Arizona and Nevada and as far away as the San Francisco Bay Area, Sacramento, and Baja California in Mexico. The damage was relatively minor, as the Ridgecrest area is in sparsely populated Kern County. There was one death and 25 injuries.

The creeping of the Garlock fault shows the damage that this year’s Ridgecrest earthquake caused in the desert region of California, which lies perched between the Sierra Nevada and Death Valley.

Other faults in the region are also experiencing movement, including the Little Lake and Airport Lake fault zones. The nearest population zone to these faults is the city of Ridgecrest. The rest of the region is the primarily unpopulated Mojave Desert.

Despite the low chance of a major quake, Page says California residents should always be prepared.

“It’s very frustrating trying to get people to make themselves safe when they don’t necessarily know that it’ll happen anytime soon. But there is a good chance that it’ll happen in their lifetime. So, it’s still something we need to prepare for,” Page said.

The state of California is highly prone to earthquakes, and the southern region of the state is expected to have a major earthquake along the roughly 300-mile San Andreas Fault roughly every 150 years, while the northern region is expected to have one roughly every 200 years.