Spectral characteristics of seismic noise at a site subjected to cultural interference sources

Abstract

Observations of P and S arrival times on a seismogram can be affected by ambient noise from a variety of natural and artificial sources. In order to assess the convenience of a site prone to high levels of cultural interference, we calculated the Power Spectral Density (PSD) of seismic noise in the frequency band between 1 and 40 Hz registered by the vertical component of a short-period Raspberry Shake 1D sensor, which has a flat amplitude response curve between 1 and 20 Hz. PSD curves were obtained for 56 fifteen-minute windows of ambient noise ocurring at 00, 03, 06, 09, 12, 15, 18, and 21 hours for an entire week with the aim of exploring the daily and hourly variations of noise amplitude. Our results are indicative of the antropogenic nature of the signal and the absense of transient sources of natural noise, like wind or rain. Comparison of PSD estimates with standardized models of seismic noise suggests that the ambient noise levels at our station do not exceed representative values of high ambient noise activity registered in seismological stations worldwide. Our results and review of the limitations imposed by the sensor self-noise and frequency response are relevant for a fast preliminary evaluation of potential sites for future stations.