A Study of Seismic Noise Level at the KNET Stations
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udy of Seismic Noise Level at the KNET Stations N. A. Sychevaa, I. V. Sychevb, A. N. Mansurova, and S. I. Kuzikova, * a
Research Station, Russian Academy of Sciences, Bishkek-49, 720049 Kyrgyzstan Trofimuk Institute of Petroleum Geology and Geophysics (IPGG), Siberian Branch, Russian Academy of Sciences, prosp. Akademika Koptyuga, 3, Novosibirsk, 630090 Russia *e-mail: [email protected]
b
Received September 21, 2019; revised September 21, 2019; accepted March 31, 2020
Abstract—We estimated the level of seismic noise for stations of the KyrgyzNetwork (KNET) for 19 years of its operation (1999–2017) in real time. For each channel of a seismic station (east–west, north–south, vertical) we selected fifteen-minute segments of 100-Hz seismic noise distributed over all seasons of the year (March, June, September, and December) and several times of the day (0, 6, 12, and 18 h UTC). We calculated power spectral densities of seismic noise and found the probability density of signal power spectral density for all selected frequencies/periods. The resulting distributions were compared with Peterson’s seismic noise models (Peterson, 1993). The maximum absence of stochastic noise occurred at 00 and 18 h UTC for all KNET stations. The level of seismic noise is little affected by the seasons at periods of 2–5 s, slightly lowering in the summer and increasing in the cold seasons at periods of 5–10 s. September is the less favorable for periods of 0.02–2 s. The stations as a whole possess good characteristics at periods of 0.02–10 s (frequencies of 0.1–50 Hz) and can well be said to be noiseless. Keywords: KNET, station, channel, seismic records, seismic noise, power spectral density DOI: 10.1134/S0742046320040065
INTRODUCTION The Kyrgyz seismological network, KNET (KyrgyzNet), was installed in August–September 1991 by coordinated effort of several organizations, viz., the Institute of Geophysics and Planetary Physics, University California San Diego (IGPP-UCSD), the Kyrgyz Institute of Seismology (KIS), the Institute for High Temperatures of the Russian Academy of Sciences (IHT RAS), the Institute of Physics of the Earth RAS (IPE RAS), and the Indiana State University (ISU). At the time the KNET was set up, it was one of the more advanced networks worldwide. Ten stations were equipped with broadband seismometers. These included 16-bit digital converters which encompass 90 dB of recorded dynamic range. One important advantage of this network consists in the fact that all seismographs are installed on bedrock, providing for a minimum of noise. Prior to 1991, most seismic stations in Central Asia used analog instruments with limited frequency response functions. This was only sufficient for few problems to deal with, viz., event location, earthquake catalogs, focal mechanisms of earthquakes, and other problems that do not require advanced technologies. The installation of digital KNET seismographs of the new generation yielded data with a higher resolution that were amenable to high technology processing.
Six KNET stations surround the
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