A magnitude-5.1 earthquake centered in northern Orange County rippled across the Los Angeles Basin, and preliminary indications suggest the long-feared Puente Hills thrust fault may have caused it.
The quake caused pictures to fall of walls, glass items to shatter and furniture to tumble down in some homes near the epicenter. There were also reports of some gas and water line damage as well as scattered power outages.
At a home in San Dimas, dozens of pictures flew off walls, a ladder fell and dented a car in garage and medicine cabinets flew open and emptied out. In Orange, a few miles to the east of the epicenter, patrons at a BJ's pub went from boisterous conversation to tense silence. The suspended LED lights swayed. The vodka behind the bar stayed where it was. When the quake was over, the room erupted in applause.
At Disneyland, some rides were shut down as a precaution, according to guests there. Los Angeles officials said they had no reports of damage in the city.
Brea police said there were some minor injuries during a rockslide in Carbon Canyon, which caused a car to overturn. Carbon Canyon Road is closed, police said.
The main shock hit at 9:09 p.m. near Brea, with the epicenter only about 2 to 3 miles underneath the surface, which "means the shaking is very concentrated in a small area," Caltech seismologist Egill Hauksson said.
The very first indications are that the quake is "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," Hauksson said.
The 1987 earthquake was a magnitude 5.9 temblor that killing eight people and injured several hundred. It also caused $358 million in damage. More than 100 single-family homes and more than 1,300 apartment units were destroyed.
Hauksson said the earthquake sequence was unusual in that the 5.1 quake was preceded about an hour earlier, at 8:03 p.m., by a weaker foreshock of 3.6.
More than 20 aftershocks have hit the region. 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. Scientists are particularly concerned about the Puente Hills thrust fault because it goes directly underneath downtown Los Angeles. It was discovered only in 1999.
"This is the fault that could eat L.A.," seismologist Sue Hough told The Times in 2003. The Puente Hills fault system was unknown to scientists when it ruptured in 1987, causing the Whittier Narrows earthquake.
The Puente Hills runs through a large swath of densely populated Los Angeles County and is capable of producing a devastating, magnitude 7.5 quake.
It is a broad, rectangular area 25 miles long and 15 miles wide, stretching from the Puente Hills near Whittier through downtown L.A., USC and Dodger Stadium and veering west toward Beverly Hills.
In the 1970s, seismologists had thought that the worst quake to hit downtown would be a magnitude 5. But that all changed in 1999 when they discovered the Puente Hills fault. The surface of the fault plane cuts through the buried rocks like an angled sheet of paper, with its highest edge slanting up to the west and its deepest to the east. It lies about two miles under Dodger Stadium and four miles below downtown L.A.'s high-rise district. Its lowest point is nine miles underground, north of Whittier.
Another problem is that the shape of the Puente Hills fault system funnels energy toward Los Angeles' densest neighborhoods.
Video simulations show energy from a quake erupting, with the strongest waves rippling to the west and south across the Los Angeles Basin. By contrast, the magnitude 6.7 Northridge earthquake in 1994 that killed 60 people channeled its strongest shaking north to sparsely populated mountains.
Vin Scully was calling the Freeway Series at Dodger Stadium on Friday night when the 5.1 quake took place. It occurred during the sixth inning.
"A little tremor in the ballpark," Scully said. "I am not sure if the folks felt it, but we certainly felt it here."
"A tremor and only that thank goodness," he added.
The baseball game went on without incident.
Scully later recalled the massive 1989 Loma Prieta earthquake in the Bay Area, which occurred just before a game of the World Series.