A day after a powerful quake rattled Southern California, residents across the region were shaken by a 7.1 temblor that rattled for up to 40 seconds, knocked out power and frayed already thin nerves.

The earthquake struck at 8:16 p.m. Friday as part of an earthquake swarm in the Searles Valley, according to the U.S. Geological Survey. The earthquake struck nearly 9 miles west-southwest of Searles Valley and was felt as far away as Arizona. In Los Angeles, sustained swaying was reporting from the San Fernando Valley to southern Orange County.

The quake happened in the same location where a 6.4 quake happened Thursday, according to the U.S. Geological Survey.

"Every earthquake makes another earthquake more likely," said seismologist Lucy Jones. "Yesterday's 6.4 is now a foreshock, and that 7.1 aftershock has become the main shock."

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Officials scrambled to assess the damage as Gov. Gavin Newsom activated the state's Office of Emergency Services.

The governor also issued a statement Friday offering support to those affected by the earthquake. In addition, he formally requested federal assistance.

"Earlier this evening I formally requested a Presidential Emergency Declaration for Direct Federal Assistance to further support emergency response and recovery in impacted communities."

The LA Department of Water and Power reported an outage possibly in a part of the San Fernando Valley, affecting about 1,000 customers.

NBCLA viewers in Irvine record chandeliers moving during 7.1 earthquake focused in Ridgecrest.

There were no reports of damage on the Metro rail system, LAPD Chief Michel Moore reported. But there were delays on various lines as crews inspected tracks. There were no damages at Los Angeles International Airport or Ontario International Airport.

LA fire officials reported no serious injuries or signs of major damage. But in Kern and San Bernardino counties, officials reported cracked buildings and injuries. Urban Search and Rescue teams from LA and Orange counties were being deployed to Kern County to help with the damage there as they deal with a backlog of calls.

[NATL]PHOTOS: 7.1 Magnitude Earthquake Rocks Southern California

In an only-in-LA story, the Dodgers continued to play their game against the Padres at home as cameras rocked and announcers noted "another earthquake going" like Thursday.

NBA Summer League games in Las Vegas were stopped for the day as the announcer tried to calm visitors as they started to flee.

People who felt it blitzed social media.

A Disneyland parkgoer tweeted that everyone was evacuated from the new ride, the Millennium Falcon. Park officials there and at Knott's Berry Farm halted rides to inspect them.

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Another person reported feeling dizzy and his dog threw up. Chandeliers and hanging plants swayed. Pools sloshed. Electrical wires rocked.

"I thought I was getting dizzy," said Maria Solorzano in Pasadena. "It started off slow then it went faster."

Matt Tenorio said it was an undulating quake.

"Not jerky like a sine wave," he said.

Cynthia Mikimoto didn't know what it was at first.

"Then we noticed signs were shaking, a roll, like on a cruise ship," she said.

Eddie Zarate felt a rolling.

"Took quite a long while for it to stop," he said.