Cascade Range Current Update

A large earthquake (magnitude 6.8 centered about 11 miles northeast of Olympia at a depth of about 33 miles occurred this morning at 10:54 PST. There are reports of widespread damage in the Seattle, Tacoma, and Olympia areas. The earthquake signal saturated the seismic stations at Mount St. Helens for several minutes and detectable ground vibrations continued for tens of minutes. Observers from the U.S. Forest Service and Weyerhaeuser Corporation reported that there were no new large rock or snow avalanches from the crater walls or flanks of the volcano. The gage that measures the level of Castle Lake indicated a small wave (a few inches high) sloshed across the lake. Local seismicity remains unchanged since the main shock.

No changes in local seismicity have been observed at Mount Rainier either since the main shock. The Puyallup valley lahar-detection system responded to the main shock, but since the parameters necessary for lahar detection were not met, the system returned to its normal mode. This is the first test of the system's response to a large-magnitude local earthquake and it responded as designed.

Volcanoes in the Cascade Range are all at normal levels of background seismicity. These include Mount Baker, Glacier Peak, Mount Rainier, Mount Adams, and Mount St. Helens in Washington State; Mount Hood, Mount Jefferson, Three Sisters, Newberry, and Crater Lake, in Oregon; and Medicine Lake, Mount Shasta, and Lassen Peak in northern California.

USGS Cascades Volcano Observatory, the Pacific Northwest Seismograph Network at the University of Washington, and the USGS Northern California Seismic Network and Volcano Hazards Team in Menlo Park, California, monitor the major volcanoes in the Cascade Range of northern California, Oregon, and Washington.



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