7.5/5.1/4.1 Quakes on California Fault could Kill Many/Cost $Billions
 

Updated 10:07 AM EDT, Sat March 29, 2014
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A 5.1- magnitude earthquake struck the Los Angeles area Friday night, jolting nearby communities and breaking water mains in some neighborhoods.

Its epicenter was in Orange County, one mile east of La Habra and four miles north of Fullerton, the U.S. Geological Survey said.

Shortly after the earthquake, nearly two dozen aftershocks followed.

Authorities said police and local fire departments assessed affected areas and found no damage or significant injuries. One minor injury was reported in Orange County, emergency officials said.

"Tonight's earthquake is the second in two weeks, and reminds us to be prepared," Los Angeles Mayor Eric Garcetti said.

Hours before, a 3.6-magnitude tremor struck the same area, according to the USGS.

The quakes come on the heels of a 4.4-magnitude tremor that hit near downtown Los Angeles a week ago. It shook nearby buildings, but did not cause significant damage.

Southern California has experienced relatively minor tremors since 1994, when a 6.7-magnitude quake killed dozens and caused $42 billion in damage. It now stands as the second-costliest disaster in U.S. history, after Hurricane Katrina.

Earthquakes with less than 5.5 magnitude don't usually cause significant damage or casualties, though results vary by region, geophysicist Paul Caruso said.

Damage often depends on construction codes and types of rock that exist underground, he said.

re: 7.5/5.1/4.1 Quakes on California Fault could Kill Many/Cost $Billions
 

7.5 Quake on California Fault could 'Kill 18,000 and Cost up to $250 Billion in Damage'

• Magnitude-7.5 quake on Puente Hills thrust fault could kill between 3,000 and 18,000 people
• Quake could cost up to $250 billion in damage
• Fault runs near many older buildings made of concrete in downtown LA and Hollywood
• Because fault is horizontal, intense shaking could occur over 25 by 15 mile area
• Scientists say major quake occurs along fault every 2,500 years -- but don't know when last one was
  

By AP, 31 March 2014


A bigger earthquake along the lesser-known fault that gave Southern California a moderate shake could do more damage to the region than the long-dreaded 'Big One' from the more famous San Andreas Fault, experts warn.

The Puente Hills thrust fault, which brought Friday night's magnitude-5.1 quake centered in La Habra and well over 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 magnitude-7.5 earthquake along that fault could prove more catastrophic than one along the San Andreas, which runs along the outskirts of metropolitan Southern California, seismologists said.
Such a quake along the Puente Hills fault could kill 3,000 to 18,000 people and cause up to $250 billion in damage, according to estimates from The U.S. Geological Survey.

In contrast, a larger magnitude 8 quake along the San Andreas would cause an estimated 1,800 deaths.


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The destruction wrought by a magnitude-7.5 earthquake along the Puente Hills thrust fault could be far worse
than the damage from Friday's quake, seen here, meaning up to 18,000 deaths and possibly $250 billion in damage


The shaking from a 7.5 quake in the center 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,' USGS seismologist Lucy Jones said
That would 'hit all of downtown,' Jones said. 'And everywhere from La Habra to Hollywood.'

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.

'In terms of location, it couldn't be much worse,' said James Dolan, a professor at University of Southern California's department of Earth sciences, told us in 2003 while working on a study of faults. 'Downtown L.A. is sitting on top of this thing.'

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The Puente Hills fault is horizontal and stretches through downtown LA and Hollywood -- meaning a wide area could be affected by a magnitude-7.5 quake. Here, construction workers wait for a new section of pipe to be cut after Friday's magnitude-5.1 quake


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Part of the potential problem is that the fault would hit many older concrete buildings, and damage could cost up
to $250 billion dollars. Construction workers are seen here lowering pipe after Friday's quake


And because the fault, discovered in 1999, is horizontal, heavy reverberations are likely to be felt over a wide area, roughly 25 by 15 miles.

Scientists believe a major quake happens along the fault roughly every 2,500 years -- but don't know when the last one was, the LA Times reports.

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 $350 million in damage.

About 150 aftershocks, including one of magnitude-4.1, were 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, but residents have since been allowed to return. 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.

About two dozen residents remained displaced, down from more than 80 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 Monday. An email to the mayor was not immediately returned.


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A CalTrans worker and a geologist look at a rock wall where a rockslide closed a California road on Saturday March 29.

A potential magnitude-7.5 quake from the Puente Hills thrust could be so intense it would lift heavy objects in the air

Read More:

• This fault could bring an earthquake worse than 'The Big One' http://www.latimes.com/local/lanow/la-me-ln-this-fault-that-could-bring-earthquake-worse-than-the-big-one-20140330,0,3659379.story#ixzz2xUwHPv5L
• Newfound L.A. Fault Threatens Major Quake