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Cardarelli E.,University of Rome La Sapienza | Cerreto A.,External contractor
Near Surface Geophysics | Year: 2015

A hybrid approach for seismic travel-time tomography is proposed in the case of elliptical anisotropic media. A sequential scheme is presented that combines simulating annealing with linearized least squares inversion. At first, simulated annealing is implemented to obtain a velocity model that can be used as initial guess for successive linearized least squares inversion; in the meantime, linear travel-time interpolation is diffusely used to trace ray paths and calculate travel times. The procedure was tested both for a synthetic model and a field study. Since the field study come from a previous study, uniquely solved by linearized least squares inversion without suggestions for initial guess of the velocity model, we were interested in evaluating upgrades from the hybrid approach compared with solutions coming from a single technique. We found the hybrid approach able to individuate a better velocity model with respect to a "single technique" approach, but as the improvement was slight despite the big amount of computation time needed by simulated annealing, we had also an indirect validation of the previous results of the field study. © 2015 European Association of Geoscientists & Engineers.

Cardarelli E.,University of Rome La Sapienza | Cercato M.,University of Rome La Sapienza | De Donno G.,University of Rome La Sapienza | Di Filippo G.,External Contractor
Near Surface Geophysics | Year: 2014

Piping sinkholes may naturally develop in the case of a thick overburden overlying calcareous bedrock. Their detection and imaging is a challenging task for geophysical methods, not only because of the required resolution and depth of penetration, but also because major pitfalls may arise, in such geologically complex areas, from the speculative interpretation of geophysical anomalies as geological features. Data integration from different geophysical methods is essential to remove these interpretation ambiguities, caused by large near-surface gradients and heterogeneities in the soil properties, as well as by oscillations of the water table and anomalous water circulation. We present an investigation procedure consisting of the sequential application and integrated interpretation of Electrical Resistivity Tomography (ERT), Seismic Refraction Tomography (SRT) and Self Potential (SP) measurements for locating and monitoring piping sinkholes with application to a site in Central Italy. This approach is a compromise between resolution and cost-effectiveness, and it is designed to be economically affordable by the private end user. In complex geological scenarios, it is usually not possible to rate a single geophysical technique as superior to all the others in terms of resolution, cost-effectiveness and diagnostic capability. The independent information coming from the different geophysical methods is the key to removing interpretation ambiguity when evaluating the position and the development over time of the piping sinkholes. The application of the proposed investigation procedure allowed us to individuate a small area subject to the formation of a piping sinkhole. The geophysical results were confirmed about one year after the execution of the geophysical measurements, as the site exhibited surface evidence of a piping sinkhole, with the formation of a small pond filled with sulphurous water and gases coming from below. © 2014 European Association of Geoscientists & Engineers.

Cardarelli E.,University of Rome La Sapienza | Cercato M.,University of Rome La Sapienza | Cerreto A.,External contractor | Di Filippo G.,University of Rome La Sapienza
Geophysical Prospecting | Year: 2010

Near-surface cavities can pose serious hazards to human safety, especially in highly urbanized town centres. The location of subsurface voids, the estimation of their size and the evaluation of the overburden thickness are necessary to assess the risk of collapse.In this study, electrical resistivity tomography (ERT) and seismic refraction tomography data are integrated in a joint interpretation process for cavity location in the city of Rome.ERT is a well established and widely employed method for cavity detection. However, additional information provided by seismic refraction tomography is capable of eliminating some potential pitfalls in resistivity data interpretation. We propose that the structure of the cavities defined by ERT can be used as a base to optimize seismic refraction tomography investigations within the framework of a joint interpretation process.Data integration and the insertion of a priori information are key issues for reducing the uncertainties associated with the inversion process and for optimizing both acquisition procedures and computation time.Herein, the two geophysical methods are tested on both synthetic and real data and the integration of the results is found to be successful in detecting isolated cavities and in assessing their geometrical characteristics. The cavity location inferred by geophysical non-invasive methods has been subsequently confirmed by direct inspection. © 2009 European Association of Geoscientists & Engineers.

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