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Thanks to new tools being developed by Federal and State agencies, scientists can now offer more accurate insight into the likely impacts of such tsunamis.

by Erin Burkett, John Bwarie, Justin Pressfield, Jessica Robertson, and Stephanie Ross  

A boat is mostly sunk at a harbor, surrounded by docks and other boats.
The March 11, 2011, Tohoku tsunami caused significant damage to ships and docks in Crescent City Harbor in California. A number of ships were sunk within the harbor. Because of extensive sedimentation and potential contaminated debris within the harbor, recovery efforts took more than a year to complete.

Scientists cannot predict when a great earthquake producing a trans-Pacific tsunami will occur, but thanks to new tools being developed by Federal and State agencies, scientists can now offer more accurate insight into the likely impacts of such tsunamis. This knowledge can lead officials and the public to reduce the risk of future tsunamis that hit California.

What are the potential economic impacts? Which marinas could be destroyed? Who needs to be prepared for evacuations? A recently published report looks at these questions and more.

A hypothetical yet plausible scenario was developed in which a magnitude-9.1 earthquake offshore of the Alaskan Peninsula triggers a tsunami that reaches the California coast. This scenario is detailed in the new report, The SAFRR (Science Application for Risk Reduction) Tsunami Scenario, released September 4, 2013.

Maps showing potential flooding extent in harbors if there were a tsunami wave.
Some areas that would be inundated (in red) during the SAFRR tsunami scenario. Top, in Oakland and Alameda, in the eastern San Francisco Bay area, large parts of the Oakland Airport would be flooded. Bottom, in Newport Beach, Orange County, there would be complete or partial flooding of all islands and near overtopping of the Balboa Peninsula neighborhood, possibly creating evacuation challenges. From USGS Fact Sheet 2013–3081.

Some of the issues highlighted in the scenario include public safety and economic loss. In this scenario, approximately 750,000 people—about a third of them tourists and visitors—would need to be evacuated in just a few hours. Additionally, one-third of the boats and more than half of the docks in California’s marinas could be damaged or destroyed, resulting in \$700 million in losses. Total economic losses in California due to physical damage and business interruption would range from \$5–10 billion, depending on resilience strategies adopted by businesses (such as using existing inventories and working extra shifts after the tsunami). It was concluded that neither of California’s nuclear power plants would likely be damaged by this particular event.

Looking back to 2011, not only was Japan devastated by the magnitude-9.1 Tohoku earthquake and resulting tsunami, but the tsunami also swept through California and caused $50–100 million of damage. This event shows that tsunamis near and far can lead to severe economic losses in California.

The SAFRR Tsunami Scenario is a collaborative effort between the U.S. Geological Survey (USGS), the California Geological Survey, the California Governor’s Office of Emergency Services, the National Oceanic and Atmospheric Administration, other agencies, and academic and other institutions.

“The good news is that three-quarters of California’s coastline is cliffs and thus immune to the harsher and more devastating impacts tsunamis could pose,” said Lucy Jones, who is the USGS Science Advisor for Risk Reduction and leads the SAFRR Project. “The bad news is that the one-quarter at risk is some of the most economically valuable property in California.”

“In order to effectively protect communities from tsunamis, we must first know what to plan for,” continued Jones. “By starting with science, there is a clearer understanding on how tsunamis function and their potential impacts. The scenario will serve as a long-lasting resource to raise awareness and provide scientifically sound and unbiased information to decision makers in California and beyond.”

Map of harbors showing the computer modeled speed of ocean currents in a tsunami scenario.
Maximum current speeds for the Port of Los Angeles (POLA) and the Port of Long Beach (POLB) generated during the SAFRR tsunami scenario. The ports are protected by a breakwater, but during the tsunami there would be dangerously fast currents around the port entrances in the wall, locally referred to as “Angels Gate” (at POLA) and “Queens Gate” (at POLB). In the POLA, powerful currents are also expected at Cabrillo Marina and the Boat Yard, where they could break apart floating docks, damage pilings, and pull small vessels from their mooring lines. The strongest currents would be expected in the Old Navy Yard; however, there are no exposed floating assets in that immediate area. In the POLB, jet-like currents would be likely at the entrance to the main cargo container area (Pier J) and may be sufficient to damage, and possibly break, mooring lines. Image from "The SAFRR Tsunami Scenario—Improving Resilience for California" (USGS Fact Sheet 2013–3081). 

In the SAFRR scenario, scientists specifically outline the likely inundation areas, current velocities in key ports and harbors, physical damage and repair costs, economic consequences, environmental impacts, social vulnerability, emergency management, and policy implications for California.

Collaboration on the tsunami scenario was coordinated over 2 years by USGS marine geophysicist and SAFRR Tsunami Scenario project lead Stephanie Ross, who also edited and contributed to the resulting multi-chapter report and wrote the 4-page USGS Fact Sheet 2013–3081 summarizing the project findings.

On the day that the report and Fact Sheet were released, Jones and Ross launched a series of workshops convened in partnership with the California Geological Survey and the California Governor’s Office of Emergency Services and focused on discussion of the tsunami scenario. USGS scientists and partners explained the scenario and its implications to stakeholders in California coastal communities. Participants included emergency managers, maritime managers, first responders (for example, police and fire agencies), representatives of elected officials, and others. The workshops aimed to establish a community of experts while fostering the use of science in decision-making. They were hosted by the Cabrillo Marine Aquarium in Los Angeles (September 4), the Santa Barbara County Office of Emergency Management (September 5), the San Diego County Office of Emergency Management (September 6), the Santa Cruz County Office of Emergency Management (September 9), and the Port of San Francisco (September 10).

The SAFRR Project is the same USGS research project that produced the ShakeOut Scenario in 2008, examining the consequences of a probable major earthquake on the southern San Andreas Fault, and the ARkStorm Scenario in 2011, examining the risks associated with extreme rain events caused by “atmospheric rivers” moving large quantities of moisture from the equatorial Pacific Ocean to the U.S. West Coast.

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