New Los Angeles earthquake on same fault could be deadlier than 'Big One'
• Seismologists warn of danger of Puente Hills thrust fault
• 4.8 earthquake hits Yellowstone National Park
Associated Press in Los Angeles
Sunday 30 March 2014 15.11 EDT
Experts say a bigger earthquake along the same lesser-known fault that produced the 5.1-magnitude tremor that hit Los Angeles on Friday night could do more damage to the region than the long-dreaded “Big One” from the more famous San Andreas fault.
The warning came as a 4.8 earthquake shook the northern part of Yellowstone National Park early on Sunday. The University of Utah Seismograph Stations reported that the Yellowstone earthquake occurred at 6.34am about four miles north-north-east of the Norris geyser basin. The university reports it was felt in the Montana border towns of West Yellowstone and Gardiner, both about 20 miles from the epicentre.
There were no immediate reports of damage. Few visitors are in the park at this time of year. Yellowstone sees frequent small earthquakes. Since Thursday, there have been at least 25 recorded in the nation's first national park.
In California, the Puente Hills thrust fault, which brought Friday night's quake centred in La Habra and more than 100 aftershocks by Sunday, stretches from northern Orange County under downtown Los Angeles into Hollywood – a heavily populated swath of the Los Angeles area.
A 7.5-magnitude earthquake along that fault could prove more catastrophic than one along the San Andreas, which runs along the outskirts of metropolitan southern California, seismologists told the Los Angeles Times.
The US Geological Survey estimates that such a quake along the Puente Hills fault could kill 3,000 to 18,000 people and cause up to $250bn (£150bn) in damage. In contrast, a larger magnitude 8 quake along the San Andreas would cause an estimated 1,800 deaths. In 1987, the fault caused the Whittier Narrows earthquake. Still considered moderate at magnitude 5.9, that quake killed eight people and did more than $350m in damage.
Part of the problem with the potential damage is that the fault runs near so many vulnerable older buildings, many made of concrete, in downtown Los Angeles and Hollywood. And because the fault, discovered in 1999, is horizontal, heavy reverberations are likely to be felt over a wide area.
The shaking from a 7.5 quake in the centre of urban Los Angeles could be so intense it would lift heavy objects in the air, like the 1989 Loma Prieta earthquake in northern California, where the shaking was so bad "we found an upside-down grand piano", the USGS seismologist Lucy Jones told the Times.
That would "hit all of downtown," Jones said. "And everywhere from La Habra to Hollywood."
About 150 aftershocks, including one of magnitude 4.1, have been felt since Friday night's quake, which forced several dozen people in the Orange County city of Fullerton out of their homes after firefighters discovered foundation problems that made the buildings unsafe to enter, authorities said.
Fire crews red-tagged 20 apartment units after finding a major foundation crack. Structural woes, including broken chimneys and leaning, were uncovered in half a dozen single-family houses, which were also deemed unsafe to occupy until building inspectors clear the structures. Seventy residents remained displaced, down from 83 after the initial quake.
Another 14 residential structures around the city suffered lesser damage, including collapsed fireplaces. A water-main break flooded several floors of Brea City Hall, and the shaking knocked down computers and ceiling tiles, Stokes said.
It was not immediately clear if City Hall would reopen on Monday. An email to the mayor was not immediately returned.