South Whidbey fault extends to east King County, experts say

The South Whidbey fault is bigger than expected, earth experts said Thursday.

A team lead by Washington State Department of Natural Resources geologists has released maps showing that the southern Whidbey Island fault extends much farther south and east than once thought and connects to the Rattlesnake Mountain fault zone in east King County.

The South Whidbey fault is considered capable of generating equally large earthquakes. Experts say the fault represents a potential seismic hazard to residents of the Puget Lowland. The cities at greatest risk are Everett, Seattle, Port Townsend and even Victoria.

“These maps bring to light more knowledge that will help scientists and planners better understand and prepare for our state’s earthquake hazards,” said Dave Norman, state geologist and manager of the DNR Geology and Earth Resources Division.

The team determined that the Rattlesnake Mountain fault zone, which was originally mapped by DNR’s Tim Walsh in 1984, extends from near North Bend and through the Snoqualmie River Valley near Fall City and Carnation.

The new mapping shows that the Rattlesnake Mountain fault is the continuation of the south Whidbey Island fault.

In the area of North Bend, the fault zone is 4 miles wide and consists of a series of parallel faults.

Future studies by state and federal geologists will help determine the frequency and severity of earthquakes along the fault zones, officials said.

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