A Study of Seismic Noise Level at the KNET Stations

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.