DESCRIPTION:
Mount Hood Seismic Network

Felt earthquakes on Mount Hood occur every 2 years on the average. Seismic monitoring, in effect since 1977 (Weaver et.al., 1982), indicates a generalized concentration of earthquakes just south of the summit area and 2-7 kilometers below sea level.

Earthquakes occur sporadically at Mount Hood, typically as short-lived swarms of small events (less than or equal to magnitude 3.5) that locate chiefly on the south flank and below the summit at depths of less than 11 kilometers (information from USGS and University of Washington Geophysics Program). One to several swarms per year have been recorded since the seismic system was upgraded in 1980.

[Map,30K,InlineGIF]
Oregon and Southern Washington - University of Washington's Pacific Northwest Seismic Network (PNSN)
-- Modified from: University of Washington Geophysics Program, 1999, includes seismic station location map and link to PNSN

A regional seismic network operated jointly by the U.S. Geological Survey and the Geophysics Program at the University of Washington detects and locates earthquakes around Mount Hood. As many as 50 earthquakes have been recorded in one year, but the events are seldom strong enough to be felt by people on the volcano. Most occur in swarms of several events that are located below the summit area or the south flank at depths of less than 10 kilometers (6 miles). An increase in this level of earthquake activity would be noticed quickly. At monitored volcanoes similar to Mount Hood, a notable increase in seismicity has occurred days to months before the onset of eruptions.

Information on Pacific Northwest earthquake activity and hazards is provided by the Pacific Northwest Seismic Network (PNSN) which operates seismograph stations and locates earthquakes in Washington and Oregon. The PNSN is operated jointly by the University of Washington, the University of Oregon, and Oregon State University, and is funded by the U.S. Geological Survey, the Department of Energy, and the State of Washington. The PNSN is based at the Geophysics Program of the University of Washington in Seattle, and is a member of the Council of the National Seismic Systems (CNSS), a group of regional network operators who cooperate to locate and catalog earthquakes throughout the United States.

Pacific Northwest Seismic Network (PNSN) Information

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