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What is the science behind Thursday's earthquake?

How the USGS describes the type of quake felt on July 4.
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Posted at 6:06 PM, Jul 05, 2019
and last updated 2019-07-05 21:06:36-04

RIDGECREST, Calif. — What exactly is the science behind Thursday's earthquake that rattled the city of Ridgecrest and was felt by millions in southern California?

In the simplest terms, an earthquake happens when tectonic plates get stuck at their edges, according to the U.S. Geological Survey.

"When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel," USGS says on their website.

Seismologists described Thursday's event as a strike slip quake, meaning two tectonic plates moved parallel to each other but in opposite directions.

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The USGS says California has two plates, the Pacific Plate and the North American Plate. The main boundary between the plates is the 650-plus mile-long San Andreas Fault. Seismologist Dr. Lucy Jones says the San Andreas Fault was not involved in the Ridgecrest quake.

"It is an area with a lot of little faults but no long fault," she tweeted.

Ridgecrest and the surrounding areas are still feeling aftershocks over 24 hours later, and they aren't expected to let up.

The USGS says aftershocks represent minor readjustments along the portion of a fault that slipped at the time of an earthquake.

"The frequency of these aftershocks decreases with time. Historically, deep earthquakes (>30 km) are much less likely to be followed by aftershocks than shallow earthquakes," USGS said.

The July 4 quake was 10.7 km deep, according to the agency.