RIDGECREST (CBS SF/AP/CNN) — For a second day, Southern California was rocked by a major earthquake Friday — this one a 7.1 magnitude — in the same area of the Mojave Desert near Ridgecrest where a 6.4 magnitude temblor caused damage on Thursday.

The U.S. Geological Survey says the quake hit at 8:19 p.m. and was centered 11 miles from Ridgecrest. The agency initially said the earthquake had a magnitude of 7.1, downgraded it to a 6.9 but then readjusted back up to a 7.1.

If the preliminary magnitude is correct, it would be the largest Southern California quake in more than 20 years.

For continuing coverage of the earthquake, visit CBS Los Angeles.

The area in and around Ridgecrest, already trying to recover from the previous temblor, took the brunt of damage.

Megan Person, director of communications for the Kern County Fire Department, said there were reports of multiple injuries and multiple fires, but she didn’t have details.

The county opened an emergency shelter. Meanwhile, a rockslide closed State Route 178 in Kern River Canyon, where photos from witnesses also showed that a stretch of roadway had sunk.

San Bernardino County firefighters reported cracked buildings and one minor injury.

In downtown Los Angeles, offices in skyscrapers rolled and rocked for at least 30 seconds. L.A. fire officials said no major damage to infrastructure had been identified in the city.

“It is on the same fault system and it’s larger,” said Cal Tech seismologist Lucy Jones. “Still in the Owens Valley. My expectation is Ridgecrest is having a difficult time tonight.”

Jones said since Friday’s quake was larger, Thursday’s 6.4 temblor would now be considered a foreshock. The foreshock Friday morning and the 7.1 quake had lengthened the fault line to the northwest away from Los Angeles.

“The fault is growing,” Jones said.

In the hour following the 7.1 temblor, Jones said, there were at least 10 aftershocks of between 4-5 magnitude including a 5.1 at around 9:19 p.m.

The temblor was felt from Long Beach to Las Vegas. .Thursday’s quake caused major damage to buildings and roads in Ridgecrest and reports of even wider destruction began rolling in within an hour of a quake.

Officials in San Bernardino County reported homes shifting, foundation cracking and retaining walls coming down. One person suffered minor injuries and was being treated by firefighters, they said.

Andrew Lippman, who lives in suburban South Pasadena, was sitting outside and reading the paper when Friday’s quake hit.

“It just started getting stronger and stronger, and I looked into my house and the lamp started to sway. I could see power lines swaying,” he said. “This one seemed 45 (seconds)… I’m still straightening pictures.”

In Las Vegas, the quake rocked the Thomas & Mack Center where a NBA Summer League game featuring top draft pick Zion Williamson was underway. Immediately, officials halted play and fans streamed out of the facility as the massive scoreboard rocked back and forth.

The press box at Dodger Stadium lurched for several seconds, and fans in the upper deck appeared to be moving toward the exit. Enrique Hernandez of the Dodgers was at-bat in the bottom of the fourth when the quake occurred. He stepped out of the batter’s box, but it wasn’t clear if that was because of the quake.

As a comparison, the deadly Loma Prieta Earthquake that ravaged the San Francisco Bay Area in 1989 was a 6.9 magnitude temblor. The 1994 Northridge earthquake was a 6.7.

Residents living in Ridgecrest and other nearby cities and towns have been on edge since Thursday’s quake as more than 1,700 aftershocks ranging in size from 5.4 to 2.3 have rattled the region.

Zachary Ross of the California Institute of Technology says the number of aftershocks might be slightly higher than average. He also says a quake of that size could continue producing aftershocks for years.

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