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Seismic Monitoring

Hanford Seismic Monitoring Network

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Seismic Monitoring at the Hanford Site consists of 42 sensor sites in two arrays: the Hanford Seismic Monitoring Network and the Eastern Washington Seismic Monitoring Network.

The Hanford Seismic Monitoring Network detects, locates and measures the magnitude of earthquakes on the Hanford Site and nearby vicinity, and measures strong ground motion at sites near important Hanford facilities. It consists of 21 seismic sensor sites and 6 strong motion accelerometer sites and is a subnet of the Eastern Washington Seismic Network.

The Eastern Washington Seismic Monitoring Network consists of 36 sites and is jointly operated with the University of Washington as part of the Pacific Northwest Seismic Network. The information from these networks is used to estimate seismic hazards at the Hanford Site for engineering design and evaluation of facilities, and to support the Hanford Emergency Response organization in the event of a significant earthquake.

image - Rattlesnake Mountain

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Rattlesnake Mountain

Rattlesnake Mountain, at nearly 3,600 feet elevation, forms the southern boundary of the U.S. Department of Energy's Hanford Site. Rattlesnake Mountain is one of a series of anticlinal ridges that forms the Yakima Fold Belt of eastern Washington. This view is from the east and shows the steep north side of the mountain. The Rattlesnake Mountain fault, a south dipping thrust fault, marks the base of the mountain. A second smaller fault occurs at the break in slope approximately one third of the way up the mountain. The age of last movement on Rattlesnake Mountain fault is not known but faults on other Yakima folds have been shown to have moved in the past 10,000 years. Toppenish Ridge has prominent fault scarps caused by multiple fault movements over the past 165,000 years.

image - Toppenish Ridge Trench

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Toppenish Ridge Trench

Geologic studies by Newell Campbell and Ted Repasky as part of the US Geological Survey's National Earthquake Reduction Program have shown that there have been between three and five seismic events along Toppenish Ridge in the last 165,000 years. Toppenish Ridge is a Yakima fold along the west side of the Columbia Basin. This trench was excavated through one of the surface scarps and shows evidence for at least two episodes of faulting. The most recent event was between 5,000 and 7,000 years ago and produced about 6.5 feet of displacement. Campbell and Repasky estimate that this fault produced an earthquake as large as a magnitude 7.

image - Toppenish Ridge

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Surface Scarp along Toppenish Ridge

Earthquake hazards studies in the Columbia Basin have found evidence for young faulting. At Toppenish Ridge in the western part of the Columbia Basin, trenching studies by Newell Campbell have found evidence for three and possibly five, moderate to strong earthquakes in the past 165,000 years. The youngest event recorded in this trench occurred between 5,000 and 7,000 years ago. At least 21 additional sites in the Yakima Fold Belt have evidence for Pleistocene-Holocene fault movement.

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