May 6, 1996 in Nation/World

Team Connects The Dots To Map Quake Fault Line

Associated Press
 
Tags:geology

A landslide here, a broken chimney there. Those are the kind of dots scientists are connecting to map the fault that was the source of an earthquake felt throughout much of the state.

So far, the dots are aligned mostly in a 20-mile gap between two previously identified southeast-northwest fault lines - the Rattlesnake Mountain fault, which has been mapped as far north as North Bend, and the Whidbey Island fault, traced as far south as Everett.

Tim Walsh of the state Department of Natural Resources displayed transparencies showing four to five small quakes annually in the 20-mile gap.

“If you project back, the epicenter of this latest quake is right dead on it,” said Sam Johnson of the U.S. Geological Survey.

Since the quake that registered 5.4 magnitude Thursday night near Duvall, scientists have detected more than 80 aftershocks, including one that registered 3.0 at 4:06 a.m. Sunday. The biggest aftershock registered 3.6 at 7:18 a.m. Saturday.

Minute aftershocks that could continue for weeks may provide vital clues, so geologists rushed to install measuring gear in eastern King and Snohomish counties over the weekend.

Unlike the readily apparent evidence of faults in barren areas, those in the Puget Sound area are mostly hidden in forests and buried beneath the silt and gravel deposits left by glaciers in the Ice Age.

Over the weekend, scientists combed areas around the epicenter for signs of the recent quake.

In the hills near Sultan, USGS geologist Ralph Haugerud found a fresh slide that a nearby resident heard rumbling down a steep hill Thursday night.

On a logging road, new cracks as deep as 16 inches ran for about 100 feet along one shoulder.

At a house in a nearby valley, the upper half of the chimney had fallen onto the lawn and cupboards had been emptied by the quake.

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