A tsunami spawned by a huge Alaskan earthquake could hit the
California coast at any time and cause at least $10 billion in damage across the
state, teams of scientists warned Wednesday.
The disaster would force at least 750,000 people to evacuate flooded areas, destroy port facilities in the Bay Area and Los Angeles, and send water surging up creeks, harbors and canals everywhere, the scientists said.
The scenario described by experts at the U.S. Geological Survey and scores of state and national specialists proposes a "hypothetical but plausible" event caused by a magnitude 9.1 quake. An Alaskan quake of that strength would cause waves up to 24 feet high that would batter California's low-lying coastal areas with only a few hours of warning, the scientists said.
Disaster planners who have worked for years assessing potential tsunami damage to California were spurred to update their 2009 flood maps and damage assessments by the magnitude 9 Japanese earthquake and tsunami in 2011 that flooded the Fukushima nuclear power plant and has left the devastated region still fearing radiation.
Waves from that tsunami rolled across the Pacific and caused $50 million to $100 million in damage along the California coast, the planners noted.
"Although this pales in comparison to the loss of lives and property in Japan," the Geological Survey's authors wrote, "the U.S. government must ask whether California, and the national economy, will someday face worse consequences from other distant-source tsunamis. Unfortunately, the answer is 'yes.'"
The survey, led by seismologist Lucile M. Jones, recruited more than 150 specialists from universities, state and local governments and coastal industries for the massive scenario project.
Tsunamis are most noted for their towering waves that hit shorelines, but also for the currents they produce as their waters surge into bays and harbors.
"Tsunami risks are rare but real and they can be very, very devastating," Jones said. "But it isn't just high waves that cause the damage, it's also the powerful tsunami currents that move the coast. If you're in a danger zone, you don't risk watching -- you get out."
Among the experts who prepared the tsunami report was industrial engineer Keith Porter, a University of Colorado professor who focused on potential damage to the broader Bay Area, from Marin to Monterey.
He and his team estimated that flood damage throughout that region could reach $12 billion in total replacement costs -- or at least $1 billion in repairs -- in 2010 dollars, with 6 percent, or $60 million, added for today's costs.
Tsunami waves coming through the Golden Gate, Porter said, would pour over the Embarcadero and flood the BART tunnel south of Justin Herman Plaza at the foot of Market Street, demanding at least two days of pumping before trains could run again.
Flood damage would hit the low-lying areas of San Francisco and Marin, he said. "Downtown Tiburon would be inundated, for example, and the water would flood Larkspur Landing and Corte Madera Creek," Porter said.
In Alameda County, the entire island that holds the city of Alameda and the former Alameda Naval Air Base would have flooding, Porter said. The Port of Oakland, which stretches for 19 miles along the city's waterfront, would be badly damaged both by flooding and strong cross currents, and the airport would be flooded, the report said.
As an engineer, Porter estimated that high water between Monterey and Marin would damage a total of 35 million square feet of buildings -- the equivalent, he said, of 25,000 homes.
Only hours of warning
Kevin Miller, the lead tsunami researcher for the California Office of Emergency Services, said that the Bay Area would have only five hours of warning of tsunami from an offshore Alaskan quake. The warnings would be sent by the U.S. tsunami warning center in Palmer, Alaska, giving notice ranging from four hours in Crescent City to six hours in San Diego, he said.
Fourteen Bay Area counties have already erected more than 6,000 tsunami warning signs instructing residents where and how to evacuate low-lying areas, Miller said, and more are being installed every day.
The Geological Survey experts reported that tsunami damage can be minimized wherever cities, harbors and low-lying communities are "resilient," and Porter, the University of Colorado engineer, defined resilience this way:
"It's how well prepared you are to resist the damage from a tsunami, and how well you're able to bounce back."
(c)2013 the San Francisco Chronicle
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