Earthquake swarm hits California with 1,000 shakers in a less than 1 square mile

More than 1,000 small earthquakes have occurred in San Bernardino and Riverside counties in the past three weeks, running from late May to mid-June. More than 1,000 small earthquakes have occurred in San Bernardino and Riverside counties in the past three weeks, running from late May to mid-June. Photo: USGS Photo: USGS Image 1 of / 10 Caption Close Earthquake swarm hits California with 1,000 shakers in a less than 1 square mile 1 / 10 Back to Gallery

It's a reminder the ground in California is alive.

A flurry of more than 1,000 small earthquakes has rattled Southern California over the past three weeks.

The quakes have occurred in an area covering less than a square mile in San Bernardino and Riverside counties roughly 40 miles east of downtown Los Angeles.

The United States Geological Survey map depicting the uptick in seismic activity shows a thick collection of dots, a rather unsettling sight.

Residents in the area have felt the shaking and the quakes, and USGS science advisor Ken Hudnut says, "It has caused some concern among the citizens who are feeling this activity."

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Experts say earthquake swarms are typical in a state crisscrossed by active faults, but anytime they happen, Californians begin to wonder, is the Big One coming?

"The earthquake community doesn't have the ability to predict earthquakes, but what we can do is monitor them closely and that's what we're doing now," says Hudnut.

Hudnut says that while these swarms occasionally occur, each one is different.

"In detail, if you zoom in on it and look at the pattern and how it's evolving in time, it's a little different than what we've seen before," he says. "We get these swarms, but we don't see exact repeats. Obviously, it's very disruptive to the people who are feeling these earthquakes. We're watching this activity closely."

The swarm started on May 25 and has mostly included small quakes people in the area can't even feel, but there have been two magnitude 3.2 shakers, two 3.0 and one 3.1.