Computer Maps Out West Coast Tsunami

A computer model offers a grim picture of a likely side effect of a major Puget Sound-area earthquake: a massive tidal wave known as a tsunami hitting the sound at the speed of a jetliner.

"If we get a major event on the Seattle Fault, Puget Sound is going to get a major tsunami," said Hal Molfjeld, a scientist at the National Oceanic and Atmospheric Administration's Pacific Marine Environmental Laboratory.

Today a two-day workshop is to open at the NOAA lab, bringing together scientists and emergency-management experts to examine the risks of a tidal wave and how best to prepare for it.

"We know we're going to get tsunamis," said NOAA's Frank Gonzalez. "We just don't know when."

Underwater Surge

Tsunamis are huge pulses of energy caused by quakes or underwater landslides that can move through the water at 500 mph. Since 1990, 10 major tsunamis in the Pacific have killed more than 4,000 people.

Earthquakes are an inevitable part of life in western Washington, which is crisscrossed by fault lines.

Shunichi Koshimura, a Japanese researcher on loan to the NOAA lab, created a computer map of a tidal wave's progression in Puget Sound after a magnitude-7.6 quake on the Seattle Fault, which runs beneath the city.

Similar to when a large quake struck the Seattle Fault about 1,000 years ago, the model shows the southern side of the fault thrusting upward while the northern side drops. That produces a 15- to 20-foot wall of water heading mostly south on Puget Sound.

Due For a Quake

Until recently, scientists thought the Northwest faced little threat from tsunamis.

But in the late 1980s, a University of Washington geologist discovered evidence of huge quakes and tsunamis in the region. Such major quakes appeared to happen every 300 to 700 years, with the most recent in 1700.