Chances of a Large Tsunami Hitting U.S.

But Furlong’s biggest concern is the so-called Cascadia Subduction Zone, a 600-mile fault formed by the meeting of two tectonic plates off the Pacific coast between northern California and central Vancouver Island. “At some point this area will host an earthquake and tsunami comparable in size to what happened in December in Sumatra,” he said flatly. “And when it happens, we can expect a similar pattern of devastation.”

Fifteen to 20 years ago, Furlong conceded, “people thought the Cascadia zone was a very safe margin.” In the interim, however, several lines of research have converged to create a much different picture. First, researchers found deposits of sea-floor sediment in Oregon, Washington and British Columbia, in places too far inland to be reached by ordinary tidal activity. “When a tsunami comes in it’s picked up a lot of sand,” Furlong noted. “People talk about the wave looking black.”