Magnitude-5.1 earthquake hits Mexico near US border, days after magnitude-5.4 temblor

Eds: UPDATES with revised magnitude, time of quake, additional temblors.

CALEXICO, Calif. (AP) -- A magnitude-4,9 earthquake rocked the northern Baja California region of Mexico near the U.S. border on Monday, just days after the region was hit by a magnitude-5.4 temblor, authorities said.

Monday's quake, which occurred around 10:30 a.m. PST, was centered about 20 miles southeast of the border town of Mexicali at a depth of nearly 4 miles, according to the U.S. Geological Survey. The epicenter was 23 miles south-southeast of the U.S. city of Calexico.

The magnitude was revised down from an initial magnitude of 5.1.

There were no immediate reports of damage or injuries on the U.S. side, according to the Imperial County Sheriff's Department and Calexico police.

The quake was felt in California in parts of San Diego, Imperial and Orange counties and as far away as Yuma, Ariz., about 50 miles from Calexico, according to the USGS.

Early Saturday, the Mexicali area was shaken by a magnitude-5.4 quake that shut down factories and knocked out electricity for 400,000 people.

The latest temblor was likely an aftershock of the magnitude-5.4 event last week, said Julie Martinez, a geophysicist at the National Earthquake Information Center in Golden, Colo.

A swarm of smaller quakes, ranging from magnitudes 2.5 to 2.9, preceded Monday's temblor. At least five aftershocks were recorded including one registering a magnitude-3.6, the USGS said.

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U.S. Geological Survey: http://www.usgs.gov/