Quake swarm rattles border area

Residents of the Imperial Valley are living on shaky ground.

Border cities including Calexico and El Centro have been rocked since Friday by hundreds of earthquakes, from tiny to teeth-rattling. Three have registered a magnitude of 5.0 or more.

On Wednesday alone, at least three dozen earthquakes, one a 3.3, registered on the Richter scale.

The constant shaking has hindered business in the region and closed schools across the border in Mexicali.

The onslaught of temblors is known as a swarm, in which quakes of varying sizes can strike every few minutes, said Kate Hutton, a staff seismologist at Caltech. The Imperial Valley and Baja are prone to the swarms, she said; they can last a few days to a week.

Though the quakes aren’t breaking any geologic records, to Calexico resident Barbara Lopez, the shaking has seemed nonstop.

“It’s been scary,” said Lopez, a 27-year-old leasing agent who has had several sleepless nights. “You’re like constantly thinking: ‘Is the Big One going to hit? Are we prepared?’ Of course we’re not.”

Lopez has stashed her $300 mirror between the couch and the wall, along with her computer and breakable family photos. She and co-workers at Desert Properties in El Centro spent part of Tuesday running through earthquake drills in the office.

Firefighters in the region say that although the quakes are jangling people’s nerves, so far they have not caused structural damage or injuries.

“In the grand scheme of California earthquakes, they’ve been pretty mild,” said Richard Burns, a battalion chief in the El Centro Fire Department.

In recent days, the Calexico Fire Department sent a mutual assistance team across the border to Mexicali -- where many buildings would not meet U.S. seismic standards -- to check for structural failures.

More than 100 buildings in Mexicali are believed to have sustained damage, said Eric Diaz, an emergency medical technician and firefighter with the Mexicali Fire Department who is also working with the city’s office of emergency services.

Most Mexicali schools were closed Monday through Wednesday while inspectors checked the buildings’ safety, Diaz said; they are expected to reopen today.

In addition to concern about possible damage, local leaders said the heavy pedestrian border traffic between Calexico and Mexicali seemed to have slowed.

Perhaps hardest hit economically were the normally busy swap meets, said Calexico Mayor John R. Renison.

“Local merchants said it’s absolutely devastating,” Renison said.

Similar quake swarms hit the region in May 2006 and in summer and fall of 1999, said Egill Hauksson, a seismologist at Caltech.

Residents of the region say they aren’t leaving, though; the slower pace of life compensates for the sudden shock of quakes.

Even so, said Imperial County Supervisor Victor M. Carrillo: “You never get used to it.” Carrillo said he still sees people dashing out of buildings in a panic when the rattling starts, even though the largely single-story structures in the valley can usually withstand the rolling rumbles of frequent quakes.

In El Centro, coffee shop cashier Gloria Estrada said the memory of a devastating earthquake in Guatemala in 1976 had kept her running for cover in doorways at home and work over the last few days.

Seismologists say Estrada’s town and the others near it are prone to quakes for several reasons. The region rests atop not only a fault line but also a geothermal area, where past volcanic activity has kept underground rocks hot. That heats the groundwater, which could lubricate local fault lines or change underground stresses.

To Lopez, the leasing agent, the tremors feel “like a big rumble, then all of a sudden the house starts moving.”

The seismic shudders, she said, have frightened her two daughters. Fortunately she has a built-in earthquake alarm: Her two basset hounds, Tiny and Tubby, start barking each time the earth’s about to move.

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susannah.rosenblatt@latimes.com