The Faults Involved in July’s Earthquakes May Be Capable of a Bigger One

The Garlock Fault in the Mojave desert was quiet for 500 years–but it’s not looking so quiet anymore

In July, Southern California was shaken by the largest earthquake sequence to hit the region in years, centered around a fault line in the Mojave desert, some 120 miles from Los Angeles. New findings from scientists who have been studying data from the Ridgecrest Earthquake have now concluded that the network of faults involved are likely capable of producing another, stronger earthquake in the future.

The research, published this week in a paper titled “Hierarchical Interlocked Orthogonal Faulting in the 2019 Ridgecrest Earthquake Sequence,” is the work of a team of geophysicists from CalTech and NASA’s Jet Propulsion Laboratory.

Historically, scientists thought that big quakes come from big faults. The 800-mile San Andreas, for example, was seen as a major risk, in part because of its sheer size. Starting in the 1990s, that thinking began to shift after a large earthquake in Landers was pinned on multiple smaller faults operating together. The Ridgecrest Earthquake, which involved around 20 small, previously undetected faults, seems to confirm that thinking.

“We can’t just assume that the largest faults dominate the seismic hazard if many smaller faults can link up to create these major quakes,” says the paper’s lead author, CalTech professor Zachary Ross.

ridgecrest earthquake mojave fault
All earthquakes of magnitude 2.5 and greater in the Ridgecrest area July 4 to Aug. 15, 2019, are shown as gray circles. Red stars mark the two largest. The Garlock Fault south of the cluster of earthquakes has slipped almost an inch since July.

Image: USGS

In particular, those small faults in the Mojave appear to lead right up to the Garlock Fault, a 185-mile long fault line that connects Death Valley to the San Andreas. The seismic activity in July has strained the Garlock, and the scientists observed the beginning of a process called “fault creep” during the time of their study, with the fault slowly moving nearly an inch so far.

While the Garlock Fault has been considered largely dormant for the last 500 years, it appears to have awakened after July’s events. The team determined that it could be responsible for a quake with a magnitude of 8.0 on its own–though how it might connect with the just-discovered smaller faults remains unknown.

RELATED: Millions of Tiny Earthquakes Happen Without You Even Noticing

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