Seismic Studies at a Potential Deep Nuclear Waste Repository Site within the Columbia River Basalt Group, Pasco, Basin

摘要

A dense seismic network, including surface and borehole instruments, is being installed to characterize the seismicity of a proposed mined repository in Columbia River basalt on the Hanford Site. There are 11 seismic stations currently being operated by the Basalt Waste Isolation Project (BWIP), including four 1-Hz vertical surface stations, six 2-Hz 3-component surface stations, and one 4.5-Hz 3-component borehole instrument operated at a depth of 1100 m. The signal from these stations is frequency modulation telemetered to a central location, and is recorded at 200 samples/sec on an event-triggered digital recording system. Eight to 10 additional shallow (200 to 300 m) borehole seismometers may be added, pending a review of the repository network requirements prior to construction, and nine additional surface instruments are operated in support of other nuclear projects. The repository network presently has a station spacing of 5 to 10 km, compared to 25 km provided by the University of Washington (UW) regional network. Regional monitoring has observed the occurrence of shallow earthquake swarm activity in the basalts. The objective of the site-specific monitoring is to investigate the location of low-level (magnitude greater than or equal to 0) events, to search for zones of stress release, to measure the seismic moments and stress drops of the sources, and to evaluate the impacts of such microearthquakes on repository performance. (ERA citation 08:027786)