Tsunami Scenario: Magnitude 9.1 in Alaska, Problems at Ports of LA, LB Could Impact the Pass

The U.S. Geological Survey on Wednesday Sept. 4 released a report outlining a "hypothetical but plausible" tsunami created by a magnitude 9.1 earthquake offshore of the Alaskan peninsula, with analysis of potential impacts on the California coast including L.A. and Orange counties.

It's 95 miles from Banning to the Port of Los Angeles. Scenario tsunami waves won't hit the Pass, but the study indicates such an event could have economic and other impacts far inland.


The study simulates an earthquake that occurs at 11:57 a.m. PDT on Thursday March 27, 2014. Travel times to California from occurrence of the 9.1 quake to arrival of the first tsunami waves range from 4 hours in Crescent City to almost 6 hours in San Diego, according to the USGS.

In the scenario, tsunami warnings and wave arrivals would occur during a workday afternoon.

"In most cases the largest waves arrive several hours - sometimes more than 7 hours - after the initial one," authors of the study said in their executive summary. "Especially in southern California, the tsunami waves attenuate slowly in time."

The Science Application for Risk Reduction (SAFRR) Tsunami Scenario earthquake is timed so that high tides coincide with larger wave heights, increasing areas of inundation.

Up and down the California coast, less than 40 percent of the state's maximum tsunami inundation zone is flooded in the SAFRR Tsunami Scenario, according to the USGS.

But there are 14 cities with residents in the scenario inundation area, with the largest affected areas in Long Beach and San Diego.

"Nearly 92,000 people live inside the SAFRR Tsunami Scenario inundation zone," the study's authors said. "An additional 175,000 residents would be evacuated if such an order were to be given using the state's maximum tsunami inundation zone. An estimated 81,000 employees would be in the scenario inundation zone with an additional 88,000 within the state's maximum tsunami inundation zone. Additionally, more than 260,000 visitors would be expected on California's beaches and in parks on the day of the scenario event."

Visitor numbers would be more than 1 million if the same tsunami were to occur during summer months, according to the USGS.

"An estimated 8,500 residents in the SAFRR tsunami scenario inundation zone would likely need shelter because of damage to their homes," the study's authors said.

Damage in California from the March 2011 Tohoku tsunami predicts the SAFRR scenario tsunami, which produces larger waves and currents in California than the 2011 event, would damage or sink one-third of the boats and damage or destroy more than one-half of the docks in California coastal marinas, according to the USGS.

"Fires would likely start at many sites where fuel and petrochemicals are stored in ports and marinas," the study's authors said. "Many fires during past tsunamis have been caused when flammable liquids were released, spread by water, and ignited by electrical problems. It is difficult to quantify the extent of the potential losses because they depend heavily on whether the fires spread."

The scenario tsunami also has potential to cause environmental contamination in inundated areas onshore and in coastal marine and estuarine environments, according to the USGS.

The study's authors estimated repair and replacement costs of $3.4 billion in California marinas, coastal properties, and the Ports of Los Angeles and Long Beach. The damages collectively expose about $6 billion in business interruption losses.

Potential losses could be reduced by 80 percent to 90 percent with the implementation what the study's authors call "resilience strategies."

According to the USGS, possible courses of action to strengthen tsunami-related policy and to enhance California tsunami resiliency include:

- Continue the National Tsunami Hazard Mitigation Program, TsunamiReady and affiliated state and local programs, and recruit and assist all California coastal communities, ports, and harbors to become TsunamiReady.

- Develop a coordinated and sufficiently robust policy framework for tsunami hazard assessment and mitigation planning for California coastal communities, ports, and harbors.

- Advance multihazard mitigation planning along California's coast and bays to "more holistically" address issues of future tsunami risk, sea level rise, coastal flooding and erosion, and earthquake-induced liquefaction.

"While scientists can't predict when a great earthquake producing a pan-Pacific tsunami will occur, thanks to new tools being developed by federal and state officials, scientists can now offer more accurate insight into the likely impacts when tsunamis occur," the study's authors said. "This knowledge can lead officials and the public to reduce the risk of the future tsunamis that will impact California."

The rest of the "Science Application for Risk Reduction Tsunami Scenario - Executive Summary and Introduction" is at this link.

The tsunami scenario is a collaboration between the U.S. Geological Survey, the California Geological Survey, the California Governor's Office of Emergency Services, the National Oceanic and Atmospheric Administration, other federal, state, county, and local agencies, private companies, and academic and other institutions.

Previously from Banning-Beaumont Patch:

PLATES BREAK: What 8.9-Magnitude on West Edge of Pacific Could Mean in the San Gorgonio Pass

The video attached to this report shows how the March 2011 9.0 Tohoku earthquake and tsunami impacted a community near the coast of Japan.