Suitability of 10 Hz vertical geophones for seismic noise array measurements based on frequency-wavenumber and extended spatial autocorrelation analyses

Microzonation studies using ambient noise measurements constitute a promising way for seismic hazard evaluation in urban areas. Among the existing techniques, seismic noise array measurements have become a valuable tool for estimating Vs profiles and thus, the characteristics of a soil structure. Although methods based on analysis of seismic noise are simpler, cheaper and faster than borehole drilling and down-hole or cross-hole logs to derive shear-wave velocity profiles, array deployment requires the use of several stations (broadband or short-period sensors) that are not always available. In this paper, we have compared the results obtained by 10 Hz-vertical-geophone arrays with the results provided by 1 Hz-sensor arrays. Two sites in the Bajo Segura Basin (SE Spain), with different soil characteristics, were chosen for array deployment. The comparison is carried out in terms of dispersion curves by using frequency-wavenumber (f-k) and extended spatial autocorrelation (ESAC) techniques. Both analyses show a good agreement using either 1 Hz sensors or 10 Hz geophones; moreover, they demonstrate that it is possible to extend the analysis in a frequency range much below the natural frequency of the geophones. The results of our study confirm the suitability of standard seismic refraction/reflection equipment also for ambient noise array measurements, which constitutes a cheaper and faster way for investigating soil characteristics.