WASHINGTON — The U.S. system to warn about giant waves has improved since the deadly Indian Ocean tsunami in 2004, but more work lies ahead, according to an analysis that noted at least one instance when alerts from centers in Hawaii and Alaska appeared to contract each other.

"For a tsunami warning system to be effective, it must operate flawlessly, and emergency officials must coordinate seamlessly and communicate clearly," John Orcutt of the Scripps Institution of Oceanography in La Jolla, Calif., said in a statement.

He led a National Research Council panel that studied the warning system at the request of Congress and released its report Friday.

The study found that an earthquake on June 14, 2005, off the coast of California resulted in seemingly contradictory reports that confused the media, the public and local officials.

The federal government’s two centers collect data from a variety of sources and issue warnings when a giant wave threatens coastal areas.

In the 2005 case, the Alaska center correctly warned the coastal California-Oregon region that a tsunami was possible. But just minutes later, the Hawaii center reported no warning was needed in its area of responsibility, which includes Mexico.

Both were correct. But emergency managers in California, who saw both reports, were confused and some got the impression that the all-clear from Hawaii canceled the warning from Alaska.

The report recommended better coordination between the two centers. It also noted that the reason for two centers was for one to back up the other, but they do not operate that way, "creating an illusion of redundancy that could prove dangerous and costly."

The experts urged changes in the centers’ management, operations and organizational culture. That includes deciding whether the centers should issue a single message or whether a single, centrally managed center should be created, in the model of the National Hurricane Center in Florida.

While it noted much progress in detecting and warning about tsunamis since 2004, the study called for more ocean sensors and public education campaigns.

The National Research Council is part of the National Academy of Sciences, an independent organization chartered by Congress to advise the government on scientific matters.

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Online:

Tsunami report: http://national-academies.org