Abstract
Analysis of microseismic signals collected on an unstable rock face in the Italian Prealps
Highlights
Microseismic monitoring is a passive geophysical technique that generally implies the analysis of seismic signals with moment magnitude typically ranging between −3 and 0 (e.g. Mousavi et al.2016)
In the last 15 yr increasing research efforts have been devoted to the study of unstable rock slopes in order to improve our understanding of rock failures that are phenomena characterized by high destructive power and the lack of clearly noticeable forerunners
We found no significant improvements in Hit Rate (HR) and False Alarm Rate (FAR) values for the MS events, when using just a small subset of parameters identified by the principal component analysis (PCA) and explaining most of the variance in the parameters’ space
Summary
Microseismic monitoring is a passive geophysical technique that generally implies the analysis of seismic signals with moment magnitude typically ranging between −3 and 0 (e.g. Mousavi et al.2016). Local events involve just a limited number of channels and generally present multiple signals with a wider spectral content shifted towards higher frequencies (Figs 4e and m) We believe these events are related to the impacts of small rocks, and it is worth pointing out that most of the local events occurred close to geophone 4 (Figs 1 and 2b) that was installed on a ledge exposed to rockfalls from the upper section of the cliff. We resorted to cross-correlation, which is a mathematical operator able to evaluate the similarity and the time lag between two variables, with the aim of comparing broad-band signals recorded by the network with data sets collected by the Italian Lightning Detection Network (CESI—SIRF R ) This network consists of broad-band electromagnetic field sensors covering Italy with homogeneous efficiency of 95 per cent and about 50–60 per cent for cloud-to-ground and cloud-to-cloud events, respectively. Duration (ms) Max absolute amplitude (m s−1) Peak-to-peak amplitude (m s−1) Power (m2 s−3) Peak frequency (Hz) Centroid (Hz) Centroid standard deviation (Hz) Min frequency (Hz) Max frequency (Hz) Bandwidth (Hz) Max cross-correlation (-) Lag of max cross-correlation (ms)
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