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

Abstract

A B S T R A C TMicrozonation 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 Hzvertical-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.

On the use of microtremors for hydrocarbon detection

“…The small arrays increase the sensitivity to low signal levels and expand the signal frequency band down to 1 Hz, as reported by Rosa‐Cintas et al . (). The distance between two adjacent stations is 200 m, both in the in‐line and cross‐line directions.…”

Design and Implementation of an Arduino-Based Plug-and-Play Acquisition System for Seismic Noise Measurements

“…In the case of Catral, the measures with the Reftek equipment were carried out in 2017. Although the noise characteristics (i.e., amplitude spectra and locations of dominant sources) may be different in each of the time periods, the H/V curves at a particular site are time stable and mainly determined by the soil characteristics [12,51,52]. In this sense, we can observe some amplitude differences among the H/V curves, even when the same recorder is used (e.g., measures taken in Almoradí site with the same Reftek recorder in February and March), but the observed peaks remain approximately at the same frequencies.…”

Optimizing the number of stations in arrays measurements: Experimental outcomes for different array geometries and the f–k method

“…This area constitutes a well-known place studied in previous works (Rosa-Cintas et al, 2011, 2012a, 2012b.…”

“…The same equipment was recently used by Rosa-Cintas et al (2012b), in a similar way to Galiana-Merino et al (2011), in order to study the suitability of low-cost geophones for taking array measurements of ambient noise and estimating the dispersion curves through the f-k and the ESAC techniques. The comparison of the results obtained by 1Hz-sensors and 10Hz-vertical-geophones arrays in terms of power spectra density…”

“…Thus, based on the assumption of a stochastic wavefield, which is stationary both in time and space (Okada, 2003;Endrun et al, 2010;Rosa-Cintas et al, 2012b), we can consider proved the suitability of the 10 Hz vertical geophones for taking array measurements of ambient noise and estimating the dispersion curves down to frequencies of 2-3 Hz.…”