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If a major earthquake occurs beneath the Pacific Ocean off Oregon and Washington, in what is known as the Cascadia subduction zone, that would cause the land to drop, allowing sea level to rise another 3 to 6 feet immediately, the report said. Such a major temblor occurred 300 years ago, but becomes more likely as time passes.

In Long Beach, Wash., a town on a sandy spit at the mouth of the Columbia River, residents are more concerned about the prospects of a tsunami from such an earthquake, Mayor Bob Andrew said.

A dune separating the town from the ocean has been growing in recent years, making sea level rise less of a concern, he said.

The report was commissioned by states and federal agencies looking for detailed information so they can plan for an accelerated rate of erosion along beaches, bluffs and sand dunes that are already crumbling into the sea. In Oregon, Greg Sieglitz, a monitoring program manager at the state Watershed Enhancement Board, said they helped sponsor the study to help them evaluate land purchases of coastal wetlands.

The report differed slightly from projections currently used by California officials, with the newer study estimating lower sea levels in 2100. The study summarized published projections and updated it with an analysis of tidal gauge readings and satellite measurements along specific sites on the West Coast.

Susan Hansch, chief deputy director of the California Coastal Commission, said that “a lot of the data we had before was worldwide data or has the caveat, `Can’t be used for planning purposes.”

“It all comes down to the better data you have, the better decisions you can make,” she said.