Raspberry shake sensor field tests for unstable rock monitoring

In this work, we evaluate the performance of the Raspberry Shake 3D (RS-3D) seismometer in estimating the resonance frequencies of unstable rock blocks. In this perspective, we compared this low-cost sensor with the Nanometrics Trillium Compact 20s to assess whether RS-3D is suitable for the development of reliable rock monitoring systems. We carried out surveys on eight rock compartments located both in the Northern Italy and in the Maltese archipelago. Ambient noise recordings have been processed by computing the mean amplitude spectra, the ratio between the Raspberry Shake spectra and the Trillium ones, and the Horizontal-to-Vertical Spectral Ratio. The obtained results show that the RS-3D performs according to the vendor specifications, with slight spectral differences with respect to the Nanometrics reference. Our preliminary tests reveal that the Raspberry Shake may be a reliable sensor for estimating the fundamental frequency of unstable rock blocks provided the HV peak occurs within the RS flat frequency response, and, because of its low-cost, may promote the deployment of denser seismic monitoring networks.