• A spate of notable quakes have rattled Southern California in recent months — a reminder that the last three decades of relative seismic quiet won’t last forever.
• California is preparing for the annual ShakeOut earthquake drill, emphasizing the importance of preparedness.

It’s not your imagination: The ground beneath Southern California has been particularly unsteady as of late, with the region experiencing more moderate-sized earthquakes this year than it has in decades.

What precisely is fueling the sequence of shakers is not entirely clear, and officials warn that prior seismic activity does not necessarily mean more powerful temblors are imminent. But the series of modest shakers have many wondering what is going on.

“Earthquakes pop off around the state, and it’s a little bit like popcorn that they hit — sometimes they bunch up for reasons that we don’t understand,” said Susan Hough, seismologist for the U.S. Geological Survey. Where the quakes are

By the count of seismologist Lucy Jones, a Caltech research associate, Southern California has felt 15 independent seismic sequences this year, with at least one magnitude 4 or higher earthquake. That’s the highest annual total in the last 65 years, surpassing the 13 seen in 1988.

• The most recent — a magnitude 4 — struck before dawn Sunday near Ontario International Airport. Just in Ontario, one of the most populous cities in San Bernardino County, there have been five earthquakes of magnitude 3 or higher over the past month.
• The Malibu area has been another hot spot. There was a magnitude 4.6 earthquake on Feb. 9, strong enough to toss items off a counter; and a magnitude 4.7 on Sept. 12 — startling enough that the city’s mayor and his wife dove under their kitchen table.
• Eastside L.A. was rattled by a magnitude 4.4 earthquake centered in El Sereno on Aug. 12 and a magnitude 3.4 on June 2.
• A magnitude 5.2 earthquake, the strongest to strike the region in three years, shook Southern California on Aug. 6, with an epicenter northwest of the Grapevine. Another widely felt quake, magnitude 4.9, struck on July 29 about 13 miles northeast of Barstow.

Little help reading the tea leaves

The series of seismic disturbances has shaken the nerves of some Southern Californians — serving as an unpleasant reminder of the omnipresent threat of the Big One.

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