Wolin, Emily; van der Lee, Suzan; Bollmann, Trevor A.; Wiens, Douglas A.; Revenaugh, Justin; Darbyshire, Fiona A.; Frederiksen, Andrew W.; Stein, Seth et Wysession, Michael E.
(2015).
« Seasonal and Diurnal Variations in Long‐Period Noise at SPREE Stations: The Influence of Soil Characteristics on Shallow Stations’ Performance ».
Bulletin of the Seismological Society of America, 105(5), pp. 2433-2452.
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Résumé
The Superior Province Rifting Earthscope Experiment (SPREE) recorded
continuous seismic data over the Midcontinent Rift from April 2011 through October
2013. Analysis of power spectral density (PSD) estimates shows that horizontal noise
levels at periods >20 s vary seasonally and diurnally. During winter, horizontal noise
power at many SPREE stations is within 5 dB of nearby Transportable Array (TA)
stations. As the ground thaws, SPREE stations in fine-grained material such as silt or
clay become noisier due to changes in the mechanical properties of the soil. During
summer, the daily mean PSD value of stations in fine-grained material is approximately
10–20 dB higher than in the winter, and daytime noise levels are 20–30 dB
higher than nights. Stations in sandy material also show diurnal variations of
20–30 dB during summer, but the daily mean PSD value varies no more than 5–10 dB
during the year. Most neighboring TA stations have relatively constant daily mean
PSDs, and their horizontal components show summer diurnal variations of 10–15 dB.
Some very quiet TA stations, such as SPMN, show a 5–10 dB increase in horizontal
noise power during winter. The timing and amplitude of horizontal noise power variations
between 20 and 800 s correlate with variations in atmospheric pressure PSDs.
We propose that the grain size and pore water content of the material surrounding a
shallow seismic station influences the local response to atmospheric pressure. Stations
that must be placed in soft sediments should be installed in sandy, well-drained
material to minimize long-period noise generated by atmospheric pressure variations.
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