4.0 Earthquake Near Castaic May Be Cause of Bump on I-5

A 4.0-magnitude earthquake centered three miles east of Castaic shook metropolitan Los Angeles on Friday morning but caused no serious damage, officials said.

A five-inch bump that Caltrans officials said may have been caused by the quake popped up in the pavement of the Golden State Freeway north of Santa Clarita, closing two lanes for repairs.

The quake was unrelated to last week’s 5.8 temblor centered north of Sierra Madre, said Robert Finn, a spokesman for seismologists at Caltech in Pasadena.

Finn said it was impossible to tell whether Friday’s quake hinted at a larger one to come but that the probability would decline as time passes.

Caltech initially estimated the 10:41 a.m. quake at 3.6 on the Richter scale, then upgraded it to 4.0.

It measured 3.8 on the Richter scale at the U.S. Geological Survey Earthquake Information Center in Golden, Colo.

Four aftershocks measuring between 2.0 and 2.6 were recorded at Caltech over a period of two hours after the quake.

Two northbound lanes of the Golden State Freeway were shut down in the Grapevine pass area north of Santa Clarita after Caltrans workers found the five-inch-high bump in the pavement, said Jim Parsons, Caltrans superintendent for the Lebec area.

The location, about five miles south of the Gorman exit at an altitude of about 3,000 feet, is just south of an area where the San Andreas and several other faults cross the interstate, and about 23 miles northwest of the epicenter of Friday’s earthquake.

The bump resulted when two 15-foot slabs of the freeway “butted together and heaved up into the air,” Parsons said.

“It could be heat-related, or it could be earthquake-related,” he said.

“We’re not sure, but right now I think it’s probably because of the earthquake. We’ve seen it go over a 100 degrees many times here before, and we’ve never had those kinds of heat problems here.”

Parsons said the bump was discovered about 4 p.m. when “I rode over it on my way home.”

Parsons said road repairs would be completed Saturday morning.