The use of a very dense seismic array to characterize the Cavola, Northern Italy,

Abstract

The analysis of data coming from a dense 95-station array installed on the Cavola landslide (northern Apennines) is presented. The array extended along a 112X80 m2 area covered by clay deposits related to a recent and still active landslide. It operated along a four month time period in a continuous mode recording. Both earthquake and noise data are used to assess the amplification effects and relate them to thickness and geophysical properties of outcropping terrain. Compared to a reference site, earthquake data recorded on the landslide show a ground motion amplification up to a factor of 4 in the 2.5 to 5 Hz frequency band. Moreover, the study of the predominant frequency distribution derived from spectral analysis of ambient noise allows to infer thickness variations along the array. We then identify zones with small lateral variations to select sub-arrays with homogenous geometrical subsoil conditions where passive and active 1D and 2D array data analysis techniques are applied to evaluate shear waves velocity in the landslide body. Available drilling and down-hole data are used to calibrate the velocity model inferred from seismic surface data. This analysis permits to reconstruct an approximate 2D geometry used as a base for modelling waveform changes along the array.