SEISMIC BACKGROUND NOISE ANALYSIS OF BRTR (PS-43) ARRAY

Abstract:

The seismic background noise variation of BRTR array, composed of two sub
arrays located in Ankara and in Kırıkkale-Keskin, has been investigated by calculating
Power Spectral Density and Probability Density Functions for seasonal and diurnal noise
variations between 2005 and 2011. PSDs were computed within the frequency range of
100 s – 10 Hz. The results show us a little change in noise conditions in terms of time and
location. Especially, noise level changes were observed at 3-5 Hz in diurnal variations at
Keskin array and there is a 5-7 dB difference in day and night time in cultural noise band
(1-10 Hz). On the other hand, noise levels of medium period array are high in 1-2 Hz
frequency range. High noise levels were observed in daily working times when we
compared to night-time in cultural noise band. The seasonal background noise variation at
both sites also shows very similar properties to each other. Since both arrays consist of
borehole instruments and away from the coasts, we saw a small change in noise levels
caused by microseism. Comparison between Keskin short period array and Ankara
medium period array show us Keskin array is quiter than Ankara array.