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Mount Rainier Swarm Report University of Washington's Pacific Northwest Seismic Network and the USGS Cascades Volcano Observatory, September 23, 2009 Largest Event: Magnitude 2.3, NE of Mt Rainier, WA, Sunday September 20, 2009 at 09:45:27.80 AM (PDT) Magnitude: 2.3 Time: Sunday September 20, 2009 at 16:45:27.80 Z (UTC) Sunday September 20, 2009 at 09:45:27.80 AM (PDT) Distance from: 1.1 km NE of Mt Rainier, WA 39.4 km E of Eatonville, WA 93.8 km SSE of Seattle, WA (1st & Yesler) Coordinates: 46.859 deg N 121.749 deg W Depth: 3 km Quality: excellent (AA) Note: 1 km = 0.621 mile or 1 mile = 1.61 km Executive Summary: A swarm of small earthquakes started on the morning of September 20, 2009, at about 09:00 PDT beneath Mount Rainier. To date, the swarm has consisted of hundreds of earthquakes, most occurring on Sept. 20. Most locate at a depth of 2-3 km (1-2 miles) beneath the northeast flank of the volcanic edifice, centered ~1 km (0.5 miles) northeast of the summit. The largest event was a M 2.3 on Sept. 20. As of Sept. 23 swarm events continue, but at a greatly reduced rate since early on September 22. Seismic swarms are concentrations of earthquakes that typically are not initiated with a mainshock, and are common features at volcanoes. The vast majority of volcanic swarms are not associated with eruptive activity. Rainier itself has had several such swarms: in the past 7 years there have been similar days-long swarms in 2002, 2004, and 2007, two of which (2002 and 2004 )included M 3.2 earthquakes. The Sept. 20 swarm has produced the largest number of events of any swarm at Rainier since seismic monitoring began over two decades ago, so we will continue to closely monitor seismicity and other geophysical parameters at Rainier. To read more about this event (with maps and diagrams) link to the University of Washington's Pacific Northwest Seismic Network's Notable Earthquakes Special Event. View Graphic, Time vs. Depth, September 2008 to September 2009 |
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