Last weekend’s pair of powerful Ridgecrest temblors, 6.4 magnitude on Friday and 7.1 magnitude on Saturday, offered a stark reminder: “The Big One” is coming.
While the two quakes rightfully earned considerable attention, they represent something of an anomaly, as California’s three most active faultlines remain relatively calm.
“None of these are on the main faults, that is the conundrum,” said Glenn Biasi, researcher for the U.S. Geological Survey.
Biasi was part of a team that earlier this year published a report detailing the astonishing lack of large, “ground-rupturing” earthquakes, defined as magnitude 6.5 or higher, like what was seen in Ridgecrest over the weekend.
There’s nothing to show that the earthquakes last weekend could trigger a ground-rupturing earthquake on the much-busier San Andreas, San Jacinto and Hayward fault zones, Biasi said.
However, it’s possible that the area north of Ridgecrest, such as Bishop, could be at risk of another quake sometime in the future.
“When you release energy in one earthquake, sometimes it loads things farther up the fault,” Biasi said.
Like when a rivet pops out of a steel plate, Biasi said, there’s suddenly greater pressure placed on the next rivet. In the case of Ridgecrest, the first “rivet” to pop out of place might have been the 1872 Lone Pine quake, a 7.4 magnitude event.
That, followed up with earthquakes in 1992 at Joshua Tree and 1999 near Barstow, “kind of make a map, north-south on a line,” Biasi said.
Meanwhile, California’s more active faults remain curiously quiescent.
Biasi’s study found that there were eight large, ground-rupturing earthquakes along those three faults — San Andreas, San Jacinto and Hayward — between 1800 and 1918. But besides 1989 Loma Prieta earthquake, magnitude 6.9, none of the three faults have had a ground-rupturing quake in 100 years.
“We know these big faults have to carry most of the (tectonic) motion in California, and sooner or later they have to slip,” Biasi said. “The only questions are how they’re going to let go and when.”