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by Eric Mortenson, The Oregonian
Friday March 20, 2009, 8:41 PM
It's been a jittery week at eastern Washington's Hanford Nuclear Reservation, where more than 100 small earthquakes have been detected in the past seven days.
The quakes are part of an earthquake "swarm" that has puzzled scientists since it began at the first of the year. As of Friday, monitors at Hanford had detected more than 700 earthquakes since Jan. 4, said Alan Rohay, senior scientist and seismologist with Pacific Northwest National Laboratory, which operates at Hanford.
The quakes haven't disturbed the extensive stores of radioactive waste at Hanford or interfered with cleanup operations there. The plant processed plutonium for nuclear weapons during World War II and the Cold War. Highly contaminated liquid material is stored in underground tanks that have a history of leaks, and critics are wary of leaks or spills that could migrate to the nearby Columbia River.
Yellowstone Lake Earthquake Swarm Update: 2 January 2008
The University of Utah Seismograph Stations reports that as of 1800 MST on 2 January 2009, seismicity of the ongoing Yellowstone earthquake swarm continues. Over 500 earthquakes, as large as M 3.9, have been recorded by an automated earthquake system since the inception of this unusual earthquake sequence that began Dec. 27, 2008. More than 300 of these events have been reviewed and evaluated by seismic analysts. Depths of the earthquakes range from ~ 1km to around 10 km. We note that the earthquakes extend northward from central Yellowstone Lake for ~10 km toward the Fishing Bridge area, with a migration of recent earthquakes toward the north. Some of the dozen M3+ earthquakes were felt in the Lake, Grant Village and Old Faithful areas. Personnel of the Yellowstone Volcano Observatory continue to evaluate this earthquake sequence and will provide information to the NPS, USGS and the public as it evolves.
Earthquake swarms are sequences of earthquakes striking in a specific area within a short period of time. They are different from earthquakes followed by a series of aftershocks by the fact that no single earthquake in the sequence is obviously the main shock, therefore none have notable higher magnitudes than the other. An example of an earthquake swarm is the 2004 activity at Yellowstone National Park.
the inception of this unusual earthquake sequence that began Dec. 27, 2008.