The 6.8 Magnitude Puget Sound Earthquake of 2001: The Effects on Dams (and on the Dam Safety Office)

On February 28, 2001 at 10:5 a.m., a Magnitude 6.8 earthquake struck the Olympia, Washington area. This was the largest earthquake in over 50 years to hit the Puget Sound region and the first major quake since 1965. The effects were felt over a widespread area, with the greatest ground accelerations occurring between Seattle and Olympia. In the Olympia area, where the Dam Safety Office is located, the shaking was fairly strong and lasted 20-30 seconds. The Ecology building was evacuated, and employees were sent home, including dam safety staff. In accordance with Murphy's Law, I was in Eastern Washington at the time of the quake and was not even aware that it had occurred. Luckily, one of my staff remembered that we had an internal Emergency Plan (albeit in draft form since 1995), which indicated that we were to proceed to the State Emergency Operations Center at Camp Murray. State Emergency Management had no reports of failures or emergencies at any dams at that time, so our dam safety engineers proceeded to inspect the 3 high and significant hazard dams closet to the epicenter of the quake. While two of the larger dams they looked at initially had no problems, they did discover that cracks had occurred at the 20 foot high Eden Creek Dam, which supplies water to the state prison on McNeil Island. However, the reservoir had been lowered for maintenance, so there was no threat of failure at that time. By the time this inspection was completed, darkness had fallen, and further inspections would have to wait until the following dam. Thus, February 28th came to a close with no major incidents of failures reported among the 870 dams regulated solely by the Department of Ecology, Dam Safety Office. (author introduction)

Damage reports included: Eden Creek Dam, Cascades Dam at Lake Youngs, Snoqualmie Mill Pond Dam, Chambers Creek Reservoir Dam, McAllister Springs Reservoir Dam. Paper also includes maps, photographs, and summary of status of dams regulated by federal agencies. 20 pp., 11 photos.