Tiny earthquakes rattle Indio area

While not unprecedented, swarms usually closer to sea

12:31 AM, Apr. 12, 2012

There's a whole lot of shaking going on near the Coachella Valley.

According to U.S. Geological Survey, 139 small earthquakes have occurred in the past 30 days in an area between 4 and 11 miles northeast of Indio.

Most are in the magnitude-1 to -2 range, but the quakes reached magnitude-3.5 on April 3 and magnitude-3.0 on April 5. They are near but not on the San Andreas fault.

“If you saw a sequence of events right on the San Andreas, you might get a little more nervous,” said Geological Survey seismologist Susan Hough.

Research shows that historically, the southern San Andreas fault that runs along the Coachella Valley's northern edge has had a major earthquake every 150 years. But it's been at least 300 years since the last major temblor on that section of the fault.

“California has swarms like this fairly frequently,” Caltech seismologist Kate Hutton said.

Hough also called the earthquake activity “certainly not unprecedented,” but noted in the area near the valley, swarms are most often associated with the highly active geothermal areas near the Salton Sea.

“It's not entirely understood what's going on physically, but the Indio area is not a thermal volcanic area, she said.

“It's not as common to get swarms in that area. But they occur in different places in California from time to time.”

There is a small chance the earthquakes are foreshocks of a much bigger quake to come, Hutton said.

“Unfortunately, there is no way at present to tell which ones,” she said.

Hough said the chances that the small quakes could trigger a magnitude-6.0 or higher quake are “much less than 1 percent based on what we understand about earthquake statistics.”

Indio resident Ken Lummus said he hasn't felt the earthquakes at his home on Westward Ho Drive.

Like many valley residents, he said he's “semi-prepared” in the event of a major quake, but has more to do.

As for the earthquake swarm, Lummus said, “I'm concerned, but what can you do about it?”