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The Pacific Northwest Seismograph Network (PNSN) as part of ANSS
THOMAS, G.,
QAMAR, A., BARBAROPOULOU, A., LINDQUIST, P. MALONE, S.D.,
Department of Earth and Space Sciences,
University of Washington, Seattle, WA,
98195, USA;
The Pacific
Northwest Seismograph Network (PNSN) has installed 62 ANSS
strong-motion stations at locations throughout urbanized areas of
Washington and Oregon. As part of the initial phase of ANSS in 2000
PNSN installed 20 stations in time to successfully record the Mw 6.8
Nisqually earthquake in February 2001. The most recent installation is
a 4-sensor borehole array in the liquefaction-prone, industrialized
Duwamish Valley in Seattle, with the deepest sensor at 51
m. Complexities in station siting considerations have increased over
time. Driven by advice from the ANSS Regional Advisory Committee,
recent criteria have included analysis and availability of subsurface
geotechnical data, reoccupation of locations with recordings of the
1965 Ml 6.5 Olympia earthquake, and reoccupation of temporary
experimental stations with significant recordings. In addition to ANSS
supported improvements in data processing and information production
and distribution, ANSS station data have contributed to
research-related efforts. Results to date include the correlation of
peak ground accelerations during the Nisqually earthquake with shallow
sedimentary structures, which was well illustrated in the first
ShakeMap generated by PNSN. Spectral ratio analysis of surface-wave
arrivals of the M w 7.9 Denali earthquake of 3 November 2002 showed
site amplification in 0.04-0.2 Hz correlated with deep (~9 km)
sedimentary basin structures, while site amplification in 0.2-1.0 Hz
correlated with shallow sedimentary structures. Preliminary analysis
of the borehole array data suggests site amplification in 2-6 Hz
results from structures above the 51m depth sensor. Real-time data
streams from strong-motion ANSS stations have provided phase arrival
data for regional earthquakes, leading to improvements in source
locations in the regional earthquake database.
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