The University of Washington also operates one or more seismic stations at or
near nine other Cascade volcanoes,
-- (Webnote: other than Mount St. Helens) --
and, during the past few years, seismologists
have established and compared "background" levels of seismicity at several of
these volcanoes. At each volcano, signals that are larger than
pre-set threshold are categorized using the identification criteria discussed in
this paper. Correlation of signals and field observations is done when
practical; signals from debris flows and rockfalls exhibit similar
characteristics at different volcanoes (Jonientz-Trisler and Qamar, 1989;
R. D. Norris, oral commun., 1992). Even though the skill to interpret siesmic
signals at one volcano can be successfully applied to another volcano (Weaver
and others, 1990), the cause may differ from volcano to volcano. If levels of
seismicity increase above background at a volcano, more stations can be
installed to improve the ability to interpret signals and locate events.
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