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LOS ANGELES, CA — Californians pride themselves on keeping their cool when the earth shakes, but for residents in coastal Los Angeles, it’s when the shaking stops that a new scare begins.
According to scientists with the California Geological Survey, low-lying beach towns such as Santa Monica, Malibu, Venice, Marina del Rey, Redondo Beach, Long Beach, Seal Beach and Newport Beach are all vulnerable to a catastrophic tsunami. Major quakes off the coast of Alaska or Catalina Island could send a monster wave over Southern California’s coast. In some cases, residents could have hours to evacuate. In others, there would be no time for any warning. The key is knowing ahead of time the signs of a tsunami and how to escape to higher ground.
The California Geological Survey released a new interactive map Monday that shows residents if they live in a hazard zone at risk of a tsunami following an earthquake or underwater landslide. It also shows them where to flee to safety.
“It is not completely inconceivable that California could have a major tsunami,” said Steve Bohlen, acting state geologist of California and head of the CGS.
Portions of the Southern California coastline vulnerable to a tsunami are highlighted in red and yellow. Much of the coast is protected by cliffs, but low-lying beach communities in Malibu, Santa Monica, Venice, Marina del Rey, the South Bay, Long Beach and Belmont Shore-Naples remain at risk. Map courtesy of the California Geological Survey.
Ten years ago, the Tohoku-Oki earthquake and tsunami in Japan reached California’s shores, killing one person and causing $100 million in damage, he said.
A 9.3 magnitude earthquake in the Aleutian Trench off the Alaskan coastline would trigger a much larger tsunami washing over the nation’s two-largest ports and the homes of thousands of residents in Los Angeles and Orange Counties. But people would have hours to escape to higher ground in the case of a major Alaskan quake.
Undersea earthquakes near Catalina and Anacapa islands could trigger tsunamis capable of reaching local shores in minutes. And an underwater landslide off of the Palos Verdes Peninsula could send a tsunami with very little warning.
“We are talking structural damage and collapse. We are talking enough water to put people and structures at considerable risk,” said Bohlen. “That is why evacuation is so important.”
So how can Southern Californians tell a normal quake apart from one likely to cause a tsunami? If the hard shaking lasts for an extended period of time, residents in a tsunami zone should escape to higher ground without waiting for a tsunami warning, said Bohlen.
“We are talking about (a quake) that takes 20,30,40 seconds or longer, or if you see water suddenly recede — those are both signs that you should head to higher ground immediately because it has the potential for there to be a tsunami wave headed your way,” Bohlen said. “That is going to be a near-shore event, and you aren’t going to have any time to get any sort of warning. The water moves out so quickly that fish are stranding on the sand.”
In such a scenario residents should evacuate on foot, especially in densely populated beach communities.
“Your first action is to be to start walking to higher ground. If everyone gets in their car, there is going to be a massive traffic jam, and people aren’t going to be able to get out in time,” Bohlen said. “In most circumstances, if people take action quickly, they can navigate to higher ground in time to be safe.”
California residents can search their address here to see if they live in a hazard zone at risk of a tsunami. The interactive map released in honor of Tsunami Preparedness Week, also tells residents where they should run to higher ground for safety. The California Geological Survey, which released the map, said it serves two purposes. First, using new data and improved computer modeling, it updates 2009 inundation maps showing how far inland a surge of seawater might go in a worst-case scenario. And second, it ties a small buffer beyond the modeled inundation area to roads or landmarks to help local officials easily communicate evacuation plans.
Changes to the existing Los Angeles County inundation map are modest, with the inundation potential upgraded in some areas and downgraded in others, noted Rick Wilson, head of the CGS Tsunami Program. The tsunami hazard map can be found at www.conservation.ca.gov/cgs/tsunami/maps/los- angeles
The CGS and the California Governor’s Office of Emergency Services have advised several communities with isolated pockets of population and few roads for evacuation — such as in Alamitos Bay, Marina del Rey, and the ports of Long Beach and Los Angeles — about their increased inundation areas.
“A large tsunami could flood sizable areas of Marina del Rey and Long Beach to an elevation of 15 feet,” Wilson said. “Flood levels for the Port of Los Angeles and the Port of Long Beach could reach elevations of 12 to 15 feet, which would inundate almost all of the land in the ports and some of the surrounding communities. Local officials have indicated that if both ports were shut down for one day, the economic loss to the county would be over $1 billion.”
The county’s beaches can have over a million visitors per mile of beach during summer weekends and holidays, posing an evacuation challenge. According to the scenario used by CGS, the first surges of a worst-case tsunami would reach the Los Angeles coastline in about six hours.
“That may seem like a lot of time, but it will take an hour or so for the National Tsunami Warning Center to issue a warning to California and then additional time for local authorities to determine whether an evacuation is necessary,” Wilson said.
More than 150 tsunamis have hit California’s shore since 1800. Most were barely noticeable, but a few have caused fatalities or significant damage. The most destructive tsunami to hit California occurred March 28, 1964. Several surges reaching 21 feet high swept into Crescent City four hours after a magnitude 9.2 earthquake in Alaska, killing 12 people and leveling much of the town’s business district.
Scientists hope the new maps will prevent such loss of life.
“Our goal is not to scare people. It is to provide the information that helps them save their own lives,” Bohlen said. “Know where you need to go to get to high enough ground and develop your plan around that. Have a plan for connecting with family or loved ones if cell towers are down.”