As residents of a coastal zone, some Argonaut readers are concerned about the potential effect a tsunami might have on the Marina del Rey area and on nearby beach cities.
The question of whether the breakwater in the Marina harbor would provide some type of shield from a tsunami frequently arises.
County Supervisor Don Knabe recently addressed the Marina Affairs Committee of the Westchester/LAX-Marina del Rey Chamber of Commerce (now known as the LAX Coastal Area Chamber of Commerce) on the “State of the Marina.” Knabe represents the local Fourth Supervisorial District, which includes Marina del Rey, on the Los Angeles County Board of Supervisors.
One of the subjects Knabe discussed pertained to a Tsunami Preparedness Panel he had addressed in Redondo Beach.
Knabe said the panel of experts spoke about how tsunamis occur, what the potential risk is, and how Los Angeles County is working with other cities to prepare for the threat of disaster.
The National Oceanic and Atmospheric Administration operates two tsunami warning centers in the U.S. — the West Coast/ Alaska Tsunami Warning Center and the Pacific Tsunami Warning Center.
For the West Coast/Alaska Tsunami Warning Center, the area of responsibility is the U.S. West Coast as well as Alaska, Atlantic and Gulf of Mexico coasts and the east and west coasts of Canada.
The main mission of the tsunami warning center is to help protect life and property from tsunami hazard by providing information and warning messages about tsunamis within the center’s area of responsibility.
Initial tsunami bulletins are issued as soon as the earthquake’s tsunami potential has been analyzed.
Information is generated by the West Coast/Alaska Tsunami Warning Center by its “Message2” software, according to warning center documentation.
Internet, e-mail, VHF radio, satellite phone and other systems are used to disseminate information to the Federal Aviation Administration, the National Weather Service, Federal Emergency Management Agency nationwide, emergency management offices in Alaska, domestic and international government agencies, law enforcement and other institutions.
A tsunami (a Japanese word meaning “harbor wave”) is a series of waves with a long wavelength and period (time between crests) generated by a large, impulsive displacement of sea water.
Many times tsunamis are incorrectly referred to as “tidal waves” but they have no relation to the daily ocean tides.
Tsunamis can be triggered by earthquakes, landslides into or under the water surface, volcanic activity and meteorite impacts.
The question of whether the breakwater in Marina del Rey would be beneficial in slowing down waves from a tsunami received different responses from two experts.
According to local oceanologist Mark R. Legg, the breakwater “is only designed to resist large storm waves, not tsunamis.
“The long wavelength (ten to 100 miles) and period (five to 30 minutes) of a tsunami result in a local rise in sea level, like a rapid rise in the tide.
“The small breakwater at Marina del Rey would only slightly dissipate the wave energy, so the inundation and strong currents in the harbor areas would still be severe, such as during the 8.4 magnitude earthquake in Alaska in 1964, with wave oscillations higher than the tide gauge could record and lasting for about 17 hours.”
The 1964 Alaska earthquake struck Crescent City in Northern California and affected the entire coast of California, including the Marina del Rey harbor.
But Diego Arcas, of the National Oceanic and Atmospheric Administration in Seattle, responded differently, saying, “In general, the presence of a breakwater works in favor of diminishing the tsunami damage, mainly by causing the wave to break and start losing energy before it reaches the shoreline, and by reflecting some amount of the wave energy back into the open ocean.”
The West Coast/Alaska Tsunami Warning Center tracks earthquakes on a map on its Web site, wcatwc.arh.noaa.gov/
By clicking on the four-pointed red markers on the map, information can be obtained about the time, place of occurrence and magnitude of earthquakes, as well as whether or not it will generate a tsunami.
The Los Angeles County Operational Area Emergency Response Plan, which includes the Tsunami Annex, has an objective of incorporating and coordinating all county facilities and personnel, along with jurisdictional resources of the cities and special districts within the county into an efficient organization capable of responding to any emergency using the California Standardized Emergency Management System, mutual aid and other appropriate response procedures.
The county Web site — lacoa.org/doclibrary.htm — lists the Tsunami Annex information and the Tsunami Inundation map.