Millions felt the shaking from the Ridgecrest earthquake.
But it’s only watching those new satellite images that you will understand how California’s biggest earthquake in nearly two decades caused the ground to break.
Some of the clearest images show long scars on the surface of the Mojave Desert, indicating precisely the 30 miles of earthquake fault — oriented in a northwest-southeast direction — that moved within moments on July 5.
“I’ve never seen this before,” said Brian Olson, engineering geologist with the California Geological Survey. “It’s really dramatic and a super-good illustrator, even for the advanced scientists, all the way down to the grade-school kids.”
The images show “the scale of movement and the permanency of movement — this ground moved in places up to 13 feet, permanently. It’s not going back,” Olson said.
Some of the most widely circulated before-and-after GIFs that have been receiving attention by California earthquake scientists were created using imagery from Google Earth and DigitalGlobe by an earthquake geologist based in Greece, Sotiris Valkaniotis, who collaborates with the National Observatory of Athens.
In a large section of the fault, images show how land on one side of the fault moved between 3 and 13 feet from the other side, Valkaniotis said.
The animations are an impressive example of what California has undergone for millennia. California sits on the edge of two gigantic tectonic plates, the Pacific and North American. A huge swath of California, from Santa Cruz to Santa Barbara, L.A. and San Diego, is moving northwest toward Alaska relative to the other plate, which is moving southeast toward Mexico.
This kind of movement has been going on for millions of years. A famous example has been how the rock formations from a single volcano right on top of the San Andreas fault have slowly moved apart for millions of years. The western side of an ancient volcano is now in Pinnacles National Park east of the Salinas Valley; its eastern half is now 195 miles to the southeast, near the western Antelope Valley in Los Angeles County.
California isn’t being just cleanly carved along the San Andreas fault. There’s a whole array of faults slicing up the state in ribbons, and the fault that ruptured in the Ridgecrest quake on July 5 was doing its job of moving the southwestern side of land from the fault toward Alaska.
The images are among the best of their kind in decades for California. For one, the earthquakes occurred in the desert — perfect to identify the trace of a moving fault without buildings or trees obscuring cracks in the earth. “It’s easier to identify,” Valkaniotis, in a telephone interview Sunday, said of seeing the fault rupture.
“There is no vegetation … aerially, there are no land-use changes,” he said. Similar efforts to do imaging by satellite for a strong earthquake months ago in Papua New Guinea were frustrated by the region being covered in tropical vegetation, obscuring the ruptured fault from view.
The last two biggest and comparable quakes to hit the Mojave Desert in Southern California were the magnitude 7.3 Landers earthquake in 1992 and the magnitude 7.1 Hector Mine quake in 1999. But it would be years after those quakes before similar before-and-after comparisons were done, Valkaniotis said. And it was only about 20 years ago that the modern age of digital photography began.
Ground rupture was observed after the magnitude 6 Napa earthquake in 2014, but the ground displacements were much smaller, topping out at a maximum of 1½ feet, owing to the far less powerful nature of that temblor. The July 5 magnitude 7.1 Ridgecrest quake was 45 times more powerful than the Napa quake.