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COMPARISON OF NOTSSI NETWORK STATIONS- CORRECTIONS, AFTER ANALYSIS OF THE SEISMIC NOISE AND EARTHQUAKES, USING THE METHOD FOR CALCULATING THE RATIO OF THE AMPLITUDE SPECTRUES OF H-V SIGNAL COMPONENTS

Irena Aleksandrova, Dimcho Solakov, Emil Oynakov

Abstract

Eleven stations of the Bulgarian seismological network - National Operating Telemetry System for Seismological Information have been used for an assessment of the stations' corrections (site effect), to account for the impact on the seismic waves of the low-density layer immediately below the seismic stations, amplifying the signal. Nakamura's method for calculating the ratio of the spectrum of the horizontal component to the spectrum of the vertical component (H-to-V) is applied. Data from 20 local and regional earthquakes and more than 1,300 sixty-second seismic noise recordings were analyzed. The initial data are 2-hour records of seismic noise and 60-second records of earthquakes S-waves. The standard deviations are calculated - microseismic noise / earthquake. The stations’ corrections for seismic noise in the range from 0.5 to 20 Hz and S - waves of earthquakes - in the range from 0.5 to 20 Hz are estimated. For some of the stations - VTS1, PSN, KKB, KDZ, SZH, TRAN and PRD the spectral ratio curves are identical. For five of the stations - KKB, MMB, PLD, PRD and VTS1 H / V the spectral ratio fluctuates in the range 0.6 - 3, while for stations KDZ, PGB, PSN, SZH and TRAN it changes in the range 0.4 - 6. The values of A0 (f0) - amplification factor (site-effect) and f0 - resonant frequency, were obtained. A comparison of the curves of the spectral H / V ratios obtained in both ways is presented. The correlation coefficients for the curves of the spectral H / V ratios, using different methods, are obtained.

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