On the one-year anniversary of the devastating Japanese tsunami, engineers from the USC Viterbi School of Engineering Tsunami Research Center are working with the state of California to better understand the damaging currents caused by tsunamis.
Funded by the California Geological Survey, the California Emergency Management Agency and the Federal Emergency Management Agency, USC researchers will use hydrodynamic computer modeling and historical tsunami data to evaluate the currents generated by tsunamis and their effect in California ports and harbors.
Results from the study will be used to determine safe depths for evacuation, to map zones that might be prone to higher or lower currents under tsunami conditions (to inform how ships and boats are moved and evacuated) and to create hazard maps for ports, harbors and marinas. Work will begin in the next few weeks and last through the end of the year.
Currents caused by last year’s Japanese tsunami in March caused millions of dollars of damage at 27 harbors along the California coast, particularly in Santa Cruz and Crescent City. In Santa Barbara, swirling currents lasted for more than 24 hours, with the strongest surges taking place long after the original currents.
According to associate professor Patrick Lynett and adjunct research professor Jose Borrero of the USC Sonny Astani Department of Civil and Environmental Engineering, who will conduct the study, these tsunami-induced “phantom currents” are not well understood.
Even in moderate-sized tsunamis, currents can rip large boats from their moorings. During the Indian Ocean tsunami in 2004, at locations very far from the earthquake itself, large ships were ripped from their moorings and pushed around the harbor by surges occurring many hours after the tsunami first arrived.
A similar effect occurred in Crescent City in November 2006 when a magnitude 8.3 earthquake off of Russia’s Kuril Islands caused a moderate tsunami. The currents caused by the waves were strongest some three hours after the tsunami’s arrival and caused $20 million in damage to Crescent City’s harbor. Repairs from that event had not yet been completed when the Japan tsunami struck.
“Imagine an oil tanker or cargo ship torn loose and out of control in the Port of Los Angeles or San Francisco Bay,” warned Lynett, holder of the John and Dorothy Shea Early Career Chair in Civil Engineering. “The problem could escalate very quickly.”
Added Borrero: “California is being proactive in its effort to re-evaluate certain elements of its tsunami preparedness based on lessons learned from the Japan event. During [that] tsunami, even though we knew how big the waves were going to be, we severely underestimated the strength and duration of the currents.”
Rick Wilson of the California Geological Survey said, “Fortunately, this is a hazard that can be dealt with.”
His agency and the federal and state emergency management agencies are funding Lynett and Borrero, who will examine this issue as part of USC’s ongoing initiative to provide tsunami expertise to California.
Lynett and Borrero have gathered data on this phenomenon and used advanced computer models to quantify the extent and duration of the late-arriving and potentially damaging surges.
“We have the tools available to understand this problem and make the right call in the future,” Lynett said.