Second Quarter Hanford Seismic Report for Fiscal Year 2010

Rohay, Alan C. ; Sweeney, Mark D. ; Hartshorn, Donald C. ; Clayton, Ray E. ; Devary, Joseph L.

Pacific Northwest National Laboratory (U.S.)

关键词: Columbia River;    Waste Management;    Waste Storage Seismic;    58 Geosciences;    Depth;   

DOI  :  10.2172/983425
RP-ID  :  PNNL-19513
RP-ID  :  AC05-76RL01830
RP-ID  :  983425

美国|英语

来源: UNT Digital Library

【 摘 要 】

The Hanford Seismic Assessment Program (HSAP) provides an uninterrupted collection of high-quality raw and processed seismic data from the Hanford Seismic Network for the U.S. Department of Energy and its contractors. The HSAP is responsible for locating and identifying sources of seismic activity and monitoring changes in the historical pattern of seismic activity at the Hanford Site. The data are compiled, archived, and published for use by the Hanford Site for waste management, natural phenomena hazards assessments, and engineering design and construction. In addition, the HSAP works with the Hanford Site Emergency Services Organization to provide assistance in the event of a significant earthquake on the Hanford Site. The Hanford Seismic Network and the Eastern Washington Regional Network consist of 44 individual sensor sites and 15 radio relay sites maintained by the Hanford Seismic Assessment Team. The Hanford Seismic Network recorded 90 local earthquakes during the second quarter of FY 2010. Eighty-one of these earthquakes were detected in the vicinity of Wooded Island, located about eight miles north of Richland just west of the Columbia River. The Wooded Island events recorded this quarter were a continuation of the swarm events observed during the 2009 and 2010 fiscal years and reported in previous quarterly and annual reports (Rohay et al; 2009a, 2009b, 2009c, and 2010). Most of the events were considered minor (coda-length magnitude [Mc] less than 1.0) with only 1 event in the 2.0-3.0 range; the maximum magnitude event (3.0 Mc) occurred February 4, 2010 at depth 2.4 km. The average depth of the Wooded Island events during the quarter was 1.6 km with a maximum depth estimated at 3.5 km. This placed the Wooded Island events within the Columbia River Basalt Group (CRBG). The low magnitude of the Wooded Island events has made them undetectable to all but local area residents. The Hanford Strong Motion Accelerometer (SMA) network was triggered several times by these events and the SMA recordings are discussed in section 6.0. During the last year some Hanford employees working within a few miles of the swarm area and individuals living directly across the Columbia River from the swarm center have reported feeling many of the larger magnitude events. Similar earthquake swarms have been recorded near this same location in 1970, 1975 and 1988 but not with SMA readings or satellite imagery. Prior to the 1970s, earthquake swarms may have occurred at this location or elsewhere in the Columbia Basin, but equipment was not in place to record those events. The Wooded Island swarm, due its location and the limited magnitude of the events, does not appear to pose any significant risk to Hanford waste storage facilities. Since swarms of the past did not intensify in magnitude, seismologists do not expect that these events will persist or increase in intensity. However, Pacific Northwest National Laboratory (PNNL) will continue to monitor the activity. Outside of the Wooded Island swarm, nine earthquakes were recorded, seven minor events plus two events with magnitude less than 2.0 Mc. Two earthquakes were located at shallow depths (less than 4 km), three earthquakes at intermediate depths (between 4 and 9 km), most likely in the pre-basalt sediments, and four earthquakes were located at depths greater than 9 km, within the basement. Geographically, six earthquakes were located in known swarm areas and three earthquakes were classified as random events.