80,000 aftershocks and counting in Ridgecrest
Despite the high number, the quake sequence has decreased rapidly.
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 this month that aftershock sequences in areas of Earth’s crust that is 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 under which much of the earthquake rupture occurred. Coso is 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 and securing furniture and heavy appliances to walls.
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. So far, authorities believe one person has died as a result of the series of earthquakes that began with a magnitude 6.4 foreshock on July 4 — a 55-yearold man in Pahrump, Nev., about 95 miles northeast of the epicenter. Officials suspect the man, Troy Ray, was working underneath his Jeep when shaking arrived, causing the vehicle to fall on top of him.
Last week, officials said the aftershocks had been creeping into areas close to two major earthquake faults. Some aftershocks have rumbled northwest of Ridgecrest, 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, which, though lesser known, is capable of producing a quake 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.