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Scientists Create Scenario of Major Southern California Quake

Posted on: Thursday, 22 May 2008, 14:22 CDT

Scientists released a report today describing the impact of a magnitude 7.8 earthquake occurring along Southern California’s San Andreas Fault.

Although imaginary, the Shakeout Scenario is based on scientists' best predictions of what would actually occur during and after a major earthquake along the fault, and paints a grim picture of loss of life and massive infrastructure damage, including critical transportation, power, and water systems.  

A team of about 300 scientists, first responders and government and industry experts worked for more than a year to develop the devastating scenario, which will be used to prepare for the emergency.    

A report about the scenario, published by the U.S. Geological Survey (USGS) and California Geological Survey (CGS), was presented to a Congressional hearing in Washington, D.C. today, providing the most comprehensive analysis to date of the regional impact of a major Southern California earthquake.   

The quake would kill 1800 people, according to the report, but only about 700 would perish as a result of building collapses, with many others being lost to the 1,600 fires that would burn across the region.  The scenario also projects the quake would injure 50,000 people and cause $200 billion in damage, creating long-lasting social and economic consequences.   

The report predicts the strongest shaking and greatest damage would occur near the stretch of the San Andreas Fault that extends through the fastest growing areas of Southern California, including the Coachella Valley, Inland Empire and Antelope Valley.  

A summary of the report posted on the USGS Web site today describes the impact of the hypothetical scenario:

• At least 10 million people will be exposed to heavy shaking.  In spite of the large numbers of people in highly shaken areas, deaths are estimated at only 1,800 due to California’s concentrated life safety mitigation efforts.
• Building types known to be vulnerable to damage and collapse sustain major damage. All un-reinforced masonry buildings within 15 miles of the San Andreas Fault are completely destroyed.
• The fault offsets all lifelines crossing into Southern California at Cajon Pass (Interstate 15), San Gorgonio Pass (Interstate 10) and along Route 14, including pipelines, power lines, roads, railways, telecommunications and aqueducts.
• Strong shaking continues in downtown Los Angeles for 55 seconds - nearly 8 times longer than in the Northridge Earthquake.
• The prolonged, strong shaking heavily damages and sometimes collapses hundreds of old brick buildings, thousands of older industrial and commercial concrete buildings, many wood-frame buildings and even a few, high-rise steel buildings
  . Over 600,000 buildings suffer at least some damage, with tens of thousands of injuries and hundreds of deaths that leave many thousands of people without homes or jobs.
• Fire doubles the fatalities and economic losses. There will be 1,600 fires in the area large enough to warrant a 911 call, and some will merge into conflagrations that burn hundreds of city blocks.  Assuming no Santa Ana winds, the models still indicate a further $65 billion in direct losses and $22 billion in indirect losses from the fires.
• Nearly two thirds of the hospital beds are non-functional in Los Angeles, Orange, Riverside, and San Bernardino counties. At the same time, 50,000 people will seek treatment at emergency rooms.
• A $6 billion investment in seismic safety will allow the State highway system to fare well. However, some bridges are non-functional so that much of the highway is not passable on the day of the event.  
• The largest long-term economic disruption comes from damage to the water distribution system, so extensive that some areas will have to replace the entire system, with some buildings without water for as long as 6 months. Business interruption costs attributed to the lack of water will be $50 billion.

The USGS said that most of the damage is predictable, and that individuals can protect themselves and assist their communities by storing more water, keeping a fire extinguisher available and securing their space.

The scenario will be used to provide the framework for what will be the largest earthquake preparedness drill in California history, planned for November 13, 2008.  Dubbed "Golden Guardian '08," the exercise will test the ability of emergency responders to handle the impact of a magnitude 7.8 earthquake on the San Andreas Fault in Southern California. It is being jointly organized by the Governor's Office of Emergency Services and the California Office of Homeland Security, and will occur during a week-long series of public events planned for the "Great Southern California ShakeOut." A kick-off event is scheduled for June 4th to help communities plan to respond to the risks detailed in the scenario.

"The planned emergency drill is underpinned by the most comprehensive analysis ever of what a major Southern California earthquake would mean on the ground," said Dr. Lucile Jones, chief scientist for the USGS’s Southern California Multi-Hazards Demonstration Project, in a USGS press release about the report.  
"We know this science will help state and local agencies develop comprehensive emergency-response plans that will help us avoid the worst impacts of a major quake."

In the hypothetical scenario, the quake begins north of the U.S.-Mexican border near the Salton Sea, and the fault ruptures for about 200 miles in a northwest direction ending near the town of Palmdale about 40 miles north of downtown Los Angeles.   According to AP reports, the preparedness exercise will simulate the following timeline of events assuming the quake begins on Nov. 13, 2008, shortly after morning rush hour:

• 10 a.m. - A rupture occurs along the San Andreas Fault, sending shock waves at 2 miles per second throughout the region.
• 30 seconds later - The Coachella Valley begins shaking first, creating fires and the crumbling of older buildings.  Sections of the major east-west Interstate -10 break apart.
• 1 minute later -  Interstate-15, a critical north-south route would be severed in places.  Trains derail and rail lines break.  Tremors hit the counties of Riverside and San Bernardino east of Los Angeles.
• 1 minute, 30 seconds later – Violent shaking occurs in the Los Angeles basin as shock waves encompass the region.
• 2 minutes later - The rupture stops near Palmdale, but waves continue north toward coastal Santa Barbara and into the Central Valley, including the city of Bakersfield.
• 30 minutes later - Emergency responders deploy throughout the region. A magnitude-7 aftershock hits, but its energy moves south into Mexico. Several additional large aftershocks will hit in following days and months.

Major fires following the quake would cause the most damage, Keith Porter, of the University of Colorado, Boulder, who studied physical damage for the scenario, told the Associated Press.

The USGS reported last month that California has a 46 percent chance of a 7.5 or larger quake in the next 30 years, and that such a quake would probably occur in Southern California.   At magnitude 6.7, the Northridge quake, which killed 72 people and caused $25 billion in damage, was much smaller.

"We cannot keep on planning for Northridge," USGS seismologist Lucy Jones told the AP.

"The science tells us that it's not the worst we're going to face."

USGS geophysicist Kenneth Hudnut told the AP that scientists wanted to create a credible narrative and stay clear from science fiction like the 2004 miniseries "10.5" about an Armageddon-like quake on the West Coast.

"We didn't want to stretch credibility," he said.

"We didn't want to make it a worst-case scenario, but one that would have major consequences."

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On the Net:

The ShakeOut Scenario

Summary Narrative

High-resolution images and a computer animation showing the earthquake rupture and its waves of energy spreading can be viewed at http://urbanearth.usgs.gov/shakeout

Source: redOrbit Staff and Wire Reports

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