WESTMORLAND, Calif. (AP) — An earthquake swarm continued Thursday in a rural area of southeastern California with a history of such seismic activity.

The hundreds of earthquakes included a magnitude-4.9 tremor Wednesday afternoon, according to the U.S. Geological Survey.

The swarm is centered beneath agricultural fields south of the Salton Sea, about 2.5 miles (4 kilometers) northeast of the small town of Westmorland.

Notable past seismic activity in the region includes a 1981 swarm that included a magnitude 5.8 quake and a 2012 swarm that produced a magnitude 5.4 quake, the USGS said in a statement.

Past swarms have remained active for up to 20 days, but the average is about a week, the USGS said.

The USGS said the most likely scenario for the current swarm is that the rate of earthquakes will decrease over about a week’s time. A large earthquake is a much less likely scenario, the agency said.

The state on Thursday coincidentally launched a “Don’t Get Caught Off Guard” campaign to raise awareness of California’s earthquake warning system which detects the start of a quake and sends alerts so that people can protect themselves before shaking arrives.

The annual Great California ShakeOut, in which millions of people practice the “drop, cover, hold on” response to earthquakes, is scheduled for Oct. 15.

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