Mount St. Helens, Washington
Summary of Mount St. Helens Seismic Activity,
December 1996


The following information is provided by the U.S. Geological Survey's Cascades Volcano Observatory and by the University of Washington's Geophysics Program.

Earthquake activity beneath Mount St. Helens remained at a low level during December 1996. Only nine earthquakes were located beneath the volcano during the month, the lowest total since March 1995. The largest was of magnitude 0.2, the rest less than magnitude 0.0. This level of activity is within the range considered to be a safe background.

Graphic

Caption: Cross-sectional view showing the locations of earthquakes beneath Mount St. Helens during December 1996. 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). Data and graph provided by the Geophysics Program, University of Washington.

Graphic

Caption: Graph showing relationship between time and depth of earthquakes beneath Mount St. Helens from January 1, 1996 to December 31, 1996. 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). Data and graph provided by the Geophysics Program, University of Washington.