Aftershocks from the powerful 7.1 magnitude earthquake near Ridgecrest, California have been edging closer to the second-biggest fault in the state, experts warned.
The Garlock Fault is located at the edge of the Mojave Desert in Southern California and an earthquake along the fault could reach as high as 7.6 magnitude, according to the Southern California Earthquake Data Center.
“At least one section of the fault has shown movement by creep in recent years,” the center noted. There is little doubt “that the Garlock fault zone will rupture again in the future.”
Some of the thousands of aftershocks from the July 5 temblor and the 6.4 quake the day prior have been creeping closer to the Garlock Fault and another major fault, the Owens Valley fault, reported the Los Angeles Times.
The latter triggered a quake in 1872 thought to measure around 7.8 magnitude, killing 27 people with effects felt as far away as Los Angeles and Sacramento. According to the earthquake center, the probable magnitude for a quake along that fault is 6.5 to 8.2.
Here’s the problem (in part): aftershocks keeping going toward Owens Valley and Garlock faults, each capable of a magnitude 7+ quake. We don’t know if a big quake will actually be triggered any time soon. But it’s worth watching. @LATimesGraphics @ruhlmuk https://t.co/aXh4sYEboI pic.twitter.com/BjlXGqYsE0
— Ron Lin (@ronlin) July 16, 2019
The former has not had a major quake in about 465 years.
“Those are places we would be more concerned,” U.S. Geological Survey research geophysicist Morgan Page told the Times. “Little earthquakes are telling us where big earthquakes are more likely.”
She said the Panamint Valley fault is also at risk of being triggered. According to the center, that fault has a probable magnitude range of 6.5 to 7.5.
“Every earthquake actually increases the probability of more earthquakes,” she added to the Times about the raft of aftershocks. “It’s based on the idea on how a contagion spreads to a population. Earthquakes are like that … in general, if there are a lot of earthquakes going on, it’s more probable for a large earthquake to go on.”
Another expert agreed.
“We always worry when seismicity picks up very close to a major fault or if it’s at the end of a major fault—whether it’ll push it enough to start a major rupture,” added Caltech seismologist Egill Hauksson.
The 6.4 quake triggered on the Greenville Fault, according to the survey, while the 7.1 quake occurred in the Little Lake fault zone.
According to the U.S. Geological Survey, the chance of an earthquake of magnitude 7 or higher being triggered by the 7.1 temblor is 1 in 300. The agency called it “possible but with a low probability.”
There’s a 3 percent chance of a magnitude 6 or higher quake hitting.
Scientists have been warning for years about the possibility of a quake hitting along the San Andreas Fault, the biggest in the state. One said there is a 70 percent chance of a magnitude 7 or greater in Southern California before 2030.
The survey said on another page that a strong earthquake will likely not happen without warning.
“Such an earthquake may be preceded by an increase in seismicity for several years, possibly including several foreshocks of about magnitude 5 along the fault. Before the next large earthquake, seismologists also expect to record changes in the Earth’s surface, such as a shortening of survey lines across the fault, changes in elevation, and effects on strainmeters in wells,” it said.
It also explained how scientists look at parts of faults where no large quakes have happened for a while.
“Along the Earth’s plate boundaries, such as the San Andreas fault, segments exist where no large earthquakes have occurred for long intervals of time. Scientists term these segments ‘seismic gaps’ and, in general, have been successful in forecasting the time when some of the seismic gaps will produce large earthquakes. Geologic studies show that over the past 1,400 to 1,500 years large earthquakes have occurred at about 150-year intervals on the southern San Andreas fault,” it stated.
“As the last large earthquake on the southern San Andreas occurred in 1857, that section of the fault is considered a likely location for an earthquake within the next few decades. The San Francisco Bay area has a slightly lower potential for a great earthquake, as less than 100 years have passed since the great 1906 earthquake; however, moderate-sized, potentially damaging earthquakes could occur in this area at any time.”
