Preliminary data suggest Friday night's 5.1 magnitude earthquake near La Habra occurred on the Puente Hills thrust fault, which stretches from the San Gabriel Valley to downtown Los Angeles and caused the 1987 Whittier Narrows earthquake.
"It's related to the Puente Hills thrust fault, which caused the Whittier Narrows earthquake back in 1987. That may change over time as we look at the data," said Caltech seismologist Egill Hauksson.
Friday night's earthquake was centered only about 2 to 3 miles below the surface, which "means the shaking is very concentrated in a small area." Hauksson said the earthquake sequence was unusual in that the 5.1 earthquake was preceded about an hour earlier by a weaker foreshock.
Hauksson said the magnitude of the earthquake was small enough that only "some minor damage" would be expected in the La Habra and Brea areas.