LOS ANGELES — More than 80,000 earthquakes have been recorded in the Ridgecrest area since July 4 _ the aftermath from two of the biggest temblors to hit California in nearly a decade.
Experts said the two major quakes — the first measuring magnitude 6.4, the second 7.1 — led to a particularly energetic aftershock sequence before slowing down.
The calculation, conducted by Zachary Ross, Caltech assistant professor of geophysics, comes as the earthquake sequence has continued to lessen rapidly.
The U.S. Geological Survey says the chance of an earthquake of magnitude 7 or higher resulting from the Ridgecrest quakes is 1 in 300 — possible, but with a low probability.
This activity is common in areas where there’s a high heat flow in the earth, Ross said.
Caltech seismologist Egill Hauksson said earlier this month that aftershock sequences in areas of the Earth’s crust that are relatively warm can be initially quite intense but also fade more quickly, as has been seen in relatively hotter rock in the Imperial Valley.
The Ridgecrest earthquakes are relatively close to the Coso Volcanic Field of Inyo County, which is mainly within the borders of Naval Air Weapons Station China Lake, the sprawling military installation where much of the earthquake rupture occurred underneath. It’s one of the nation’s largest producers of geothermal power.
Scientists have been urging the public to use heightened concern over quakes to get prepared, including planning for a home or apartment retrofit.
In any given week, there is a 1-in-10,000 chance that a magnitude 7.8 or greater earthquake can strike the southern San Andreas fault.
The quakes caused damage in Ridgecrest, Trona and local military installations. But there were no major injuries.
Last week, officials said the aftershocks have been creeping into areas close to two major earthquake faults. Some aftershocks have rumbled northwest of the Searles Valley earthquake, approaching the Owens Valley fault. That fault triggered an earthquake of perhaps magnitude 7.8 or 7.9 in 1872, one of the largest in California’s modern record. The Ridgecrest aftershocks have also headed southeast toward the Garlock fault, a lesser-known fissure capable of producing an earthquake of magnitude 8 or higher.
New satellite images offer a dramatic and instructive view of the immense power of the magnitude 7.1 quake. The animated slides show how the temblor permanently jolted a huge block of earth northwest while the other side of the fault moved southeast.
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.
