Summary of Seismicity:
Seismicity in December is similar to that during the first 6 months of
1995. Taken together, the gradual decrease in the number of earthquakes since
September and the absence of any small explosions related to the earlier
increase in seismicity (see earlier summaries below), even during recent
periods of heavy precipitation, decrease our concern over the possibility of
future small
explosions from the dome. Such explosions are still possible, but the
likelihood of their occurrence is no greater than during the first 6 months
of 1995.
Caption: Graph showing relationship between time and depth of earthquakes beneath Mount St. Helens from January 1 to December 31, 1995. Note the gradual increase in earthquake activity between 1 and 6 miles beneath the crater from January through September, and the subsequent decrease from mid-October through December. 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 during December 1995. 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.
