1,720,966 research outputs found
Groundwater level monitoring tests with seismic interferometry
No full textThe objective of this work is to evaluate whether the seismic passive interferometry technique can be used to monitor undeground water variations in both unconfined and confined aquifers that present different hydrogeological characteristics. We collected ambient vibrations in two different water catchment fields where the water level has been artificially modified by activating a pre-existing pumping system. We first estimated the seismic velocity variations by means of Stretching technique and then compared the obtained curve with the water table level monitored by the pumping system. For both the analysed case studies, the dV/V curves showed a clear correlation with the water table variations. Moreover, this experiment reveals that different time windows of the correlogram may infer a different composition of the seismic wavefield. Provided that the absolute groundwater depth can be retrieved, the ambient noise interferometry could be employed to develop a continuous water monitoring system with dense networks for better management of the water resource
Monitoring ca lita landslide by means of the ambient seismic noise
No full textThis study presents the analysis of the ambient seismic noise recorded on the Ca Lita landslide. In this perspective, we coupled the cross-correlation and polarization techniques with the objective of investigating the variations of the unstable slope's characteristics at two different époques. The results of this study revealed that both methods provide useful information to characterize the dynamic conditions of the active landslide. In particular, the combination of the cross-correlation and polarization techniques allow studying the wavefield evolution over time which seems to be a reliable precursor of the landslide's occurrence. Therefore, the obtained results confirm the potential of ambient seismic noise analysis as a reliable tool to improve our capabilities of slopes failure forecasting
Raspberry Shake sensor field tests for unstable rock monitoring
No full textIn 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
Seismic noise monitoring of a small rock block collapse test
Full text linkWe tested the capability of seismic noise to monitor the stability conditions of a small rock block that we forced to fail in four following stages. Ambient vibrations were recorded with a broad-band 3C seismometer placed on top of the block and were processed to analyse their spectral and polarization characteristics with diverse algorithms. To analyse the spectral content of the records, we applied the multitaper method while seismic noise polarization features were investigated by means of the singular value decomposition of the Hermitian spectral density matrix. Numerical modelling was found to add limited value because of the uncertainty in estimating correctly spatial and mechanical features of the rock bridges between the block and the rock mass. Nevertheless, a modelling exercise we performed is in agreement with previous post-failure observations according to which unstable rocks may be coupled to the stable rock mass by rock bridges covering only a few per cent of the total surface of the fractures. Our analyses confirm that, when approaching final collapse, there is a trend of the block eigenmodes towards lower frequencies and show that polarized bands become narrower
Seismic noise spectral analysis techniques to monitor unstable rock blocks
No full textThis study presents the analysis of the ambient seismic noise collected on a small limestone block that was forced to fail during a field test. We compare different spectral analysis techniques with the objective of investigating their performances and suitability to monitor the rock block stability over time. Ambient vibration datasets were first pre-processed before the spectral analysis was carried out. The outcomes clearly show a variation in spectral content when approaching rock ultimate failure, especially when considering spectrograms and horizontal-to-vertical spectral ratio curves. This agrees with the assumption that the collapse of an unstable rock is preceded by a drop of its natural frequency due to the deterioration of rock bridges. The obtained results confirm the potential of ambient noise spectral analysis as a reliable tool to improve our capabilities of rock failure forecasting
Optimization of ambient seismic noise interferometry to monitor groundwater level variations
No full textConstruction of a 3D velocity model for microseismic event location on a monitored rock slope
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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