National Oceanic and
Atmospheric Administration
United States Department of Commerce

[Full Text]

FY 2010

Distant tsunami threats to the ports of Los Angeles and Long Beach, California

Uslu, B., M. Eble, V.V. Titov, and E.N. Bernard

NOAA OAR Special Report, Tsunami Hazard Assessment Special Series, Vol. 2, 100 pp (2010)

Executive Summary

Tsunamis have been recognized as a potential hazard to United States coastal communities, harbors, and ports, including those in the State of California, since multiple destructive events impacted California’s coast in the midtwentieth century. In response, the United States National Oceanic and Atmospheric Administration began a tsunami research program at the Pacific Marine Environmental Laboratory to develop tools for measuring, modeling, and assessing the hazard posed by tsunamis. The destruction and unprecedented loss of life following the December 2004 Sumatra tsunami served as the catalyst to refocus these activities, and on 20 December 2006, the United States Congress passed the “Tsunami Warning and Education Act.” The act mandated specific education and warning activities and dedicated resources to accelerate the pace of tsunami product development, including those applicable to comprehensive hazard assessment of coastal communities.

The State of California shares longer than 1,300 km of coastline with the tectonically active Pacific Ocean. Along the southern portion of this coastline, in Los Angeles County, reside two of the busiest container ports in the United States: the Port of Los Angeles and the Port of Long Beach. Adjacent to one another, the ports combine to be the fifth busiest in the world, handling more than 10 million containers annually and providing 30,000 jobs which, in turn, support the local economy. Greater than 300,000 jobs in a five-county area in Southern California are tied to the ports, as are an estimated 1.1 million jobs throughout the state. In addition, the contribution of the ports to the economy of California and to the United States as a whole is significant. Annual state and local tax revenue exceeds $5 billion (Port of Los Angeles, 2009; Port of Long Beach, 2009; Coastal Conservancy, 2009).

A tsunami impact to the ports of Los Angeles and Long Beach would potentially cause significant damage and disrupt port operations for an extended period of time. The tsunami generated by the 1964 Great Alaska Earthquake caused strong surges that tore 75 small vessels from their moorings and sank three boats in the ports of Los Angeles and Long Beach. Potential damage to the ports, and the disruption that would likely occur today, would have severe repercussions for the economy of the State of California, which relies heavily on port activities for revenue, trade, and employment. Past events and comprehensive studies of the region have documented the seismic history of the Southern California coastal region and point to the potential hazard from tsunamis. A detailed sensitivity study has been performed with synthetic tsunamis generated by Mw 9.3 earthquakes along Pacific Ocean subduction zones to identify probable maximum tsunamis. A total of 56 scenarios generated from sources along the Alaska-Aleutian subduction zone, 106 from Central and South America, 13 from the Nankai Trough and Ryuku, 28 from the Solomons and Vanuatu, 30 from New Zealand, 6 from New Guinea, 8 from Manus, 66 from the Kurils and Mariana, and 9 from the Eastern Philippines, for a total of 322 synthetic scenarios, were investigated. Of these 322 scenarios, tsunamis from 11 source regions in Alaska, Chile, Philippines, Manus, New Zealand, and Vanuatu are identified as having the potential to generate a tsunami significant to the ports of Los Angeles and Long Beach, so these are investigated in detail. Study results suggest that Mw 9.3 earthquakes can trigger a tsunami with wave amplitude reaching up to 2 m (≈6.5 ft) and currents exceeding 8 knots (≈4 m/s) in the ports of Los Angeles and Long Beach. Currents are particularly noteworthy since those exceeding 8 knots (≈4 m/s) are known to break mooring lines and damage harbor piers and other structures.

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