There were 70 well-located (quality BB or better) events at MSH last month, the most since October 1995. Of these, 21 had magnitudes >0.0 (30% of all earthquakes), with the largest a Magnitude 1.2. For reference, November had 25 events with M >0.0 (46% of the 54 total earthquakes). The cumulative seismic energy expended in December was increased relative to November, but similar to that expended in September 1997.

[Map,11K,GIF]
Mount St. Helens Seismicity - Map and Cross-Section
Cross-sectional view showing the locations of earthquakes beneath Mount St. Helens during December 1997. The cross-section represents a vertical slice of the crust downward from line A-A' in the map view. The earthquakes occurred in and around the magma conduit system that leads from the magma reservoir to the dome. In this graph, 0 depth is referenced to 1.5 km (about 1 mile) below the current summit of Mount St. Helens (8,363 feet above sea level).

[Map,9K,GIF]
Mount St. Helens Seismicity - Time vs. Depth
Graph showing relationship between time and depth of earthquakes beneath Mount St. Helens from January 1, 1997 to December 31, 1997. In this graph, 0 depth is referenced to 1.5 km (about 1 mile) below the current summit of Mount St. Helens (8,363 feet above sea level).

For More Information:
Link to: Mount St. Helens Seismicity Information -- Link courtesy University of Washington Geophysics Program