Tuesday, May 20, 2008 - Page updated at 03:20 PM

Scientists record another slow slip quake under Washington

SEATTLE —

University of Washington scientists will be collecting 100 portable instruments Thursday from an area near Port Angeles where they were arrayed to measure a slow slip tremor.

Seismology Lab Coordinator Bill Steele says over the past few weeks in an area from south Puget Sound to northern Vancouver Island the tremor slowly released energy that would be equivalent to a 6.7 magnitude earthquake if it had occurred all at once.

Steele says this is the fourth slow slip tremor that has been recorded. It is not felt. Measurements in the Pacific Northwest Seismic Network give university and U.S. Geological Survey researchers information about the mechanics and possible threat of a massive subduction zone quake like one that occurred 300 years ago in the Northwest.

Steele says these slow slip quakes tend to occur every 14 months as pressure that pushes an inch or two to the east slips partially back to the west.

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