More quakes ahead for Pacific Northwest?

By Richard Stenger
CNN.com Writer

(CNN) -- Will another powerful earthquake rip through western Washington State or the region after Wednesday's big one? Despite considerable improvements in seismology, no one knows for sure.

A 6.4 magnitude earthquake centered southwest of Seattle struck Wednesday afternoon, causing more than $1 billion worth of damage, followed by a mild aftershock Thursday morning.

Since major earthquakes happen on average in the Seattle area every 30 or 40 years, can residents of the region breathe easier for awhile?

VIDEO CNN's Ann Kellan explains the geologic forces underlying the Seattle tremor Play video (QuickTime, Real or Windows Media) CNN's David George examines a new way of reinforcing concrete that provides extra earthquake protection Play video (QuickTime, Real or Windows Media)     GALLERY Quake damage in Seattle   MAGNITUDE GUIDE Below is an interactive guide to earthquake magnitude and severity: Magnitude: Less than 3.5 3.5 - 5.4 Under 6.0 6.1 - 6.9 7.0 - 7.9 8 or greater MESSAGE BOARD Seattle shake-up

"That's impossible to predict. Another earthquake could happen tomorrow or 100 years from now," said U.S. Geological Survey spokesman Butch Kinerney.

"I don't think that the earthquake has affected the overall risk of earthquake hazards in any measurable way," said John Unger, a USGS seismologist.

While most often identified with California, earthquakes are common in the Pacific Northwest, where the edge of the Pacific Ocean plate dives far underneath the North American one.

Earthquakes happen when the two tectonic plates rub against each other in violent fashion, as they did Wednesday.

Advances over the past decades in seismology have allowed scientists to chart maps of Earthquake-prone zones and calculate the odds of quakes in particular regions over many decades or centuries.

The Puget Sound and Pacific Northwest, for example, have higher than average risks. But researchers can only localize where the greatest hazards are, not forecast when quakes will take place.

"The more we learn about earthquakes, the more elusive real predictions seem to be. The process that cause stresses and strains on the Earth's crust are extremely complex," Unger said.

The area experiences mostly weaker tremors, but quakes rated 7.0 and 6.5 struck in 1965 and 1949, the latter similar in location and depth as the one Wednesday.

Many other powerful tremors have struck over the centuries, according to geologists, including one in 1700 that trigged destructive tsunamis as far away as Japan.

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Washington State Department of Transportation Traveler Information
Washington Emergency Management Division
City of Seattle's Official Web Site
West Coast & Alaska Tsunami Warning Center
  • WC&ATWC Most Recent Event Message
  • Location Map
  • Close-up Map
Puget Sound Earthquake Origin and Occurrence
U.S. Geological Survey
The World-Wide Earthquake Locator
Understanding Earthquakes
USGS National Earthquake Information Center
Global Earthquake Response Center
Berkeley Seismology Lab

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