Mount St. Helens, Washington
Summary of Mount St. Helens Seismic Activity,
February 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 February 1996. Thirteen earthquakes were recorded during the month, compared to 14 earthquakes the previous month. The largest earthquake during February was a magnitude 2.4 event at 16:51 PST on February 21 located about 4 km (2.5 miles) directly beneath the crater. It was followed by 4 locatable aftershocks and then by about 20 very small seismic events that resembled signals typical of rock or snow avalanches. It appears that these surface events were triggered by the magnitude 2.4 earthquake that preceded them. Activity returned to normal within a few hours.

Graphic

Caption: Cross-sectional view showing the locations of earthquakes beneath Mount St. Helens during February 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.

Caption: Cross-sectional view showing the locations of earthquakes beneath Mount St. Helens between March 1, 1995 and February 29, 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.

Caption: Graph showing relationship between time and depth of earthquakes beneath Mount St. Helens from March 1, 1995 to February 29, 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.