Contribution of Geophysical Prospecting to Geohazard Evaluation

The physical properties of the subsoil are studied using geophysical methods. These studies are always indirect, such as gravimetric, magnetometric, magnetotelluric or reflection-refraction seismic surveys and are often combined to obtain more accurate and reliable results. With these tools the oil industry commonly investigates the sedimentary basins to localize structures that may favor the accumulation of hydrocarbons. Above all, seismic prospecting allow the understanding of the underground geology, defining boundaries of the geological formations as well as mechanical and physical properties of the rocks. New cutting-edge techniques allow high quality data to be obtained in almost all geological contexts and make reflection seismic the most powerful tool in subsurface observations. The seismic method was utilized in geothermal resources investigation, research of water strategic resources, volcanic risks assessment, etc. The refraction method was the first to be used in the exploration of oil reservoirs. At present the industry employs mainly refraction seismics to study shallow formations. Conversely, university researchers have applied wide-angle reflection-refraction surveys to localize deep crustal interfaces analyzing the high amplitudes of the wide-angle reflections and the velocities obtained from the refracted signals. Moho discontinuity and velocity distribution within the crust were mapped out, indicating thickness and boundary conditions in different geological settings. The maps have been used in the analysis of geodynamical behavior and of active movements within the crust, useful for seismotectonic investigations. The further addition of the seismic reflection imaging, with deep penetration and long transects, completed multidisciplinary programs to unravel the structure of the crust with clear seismic images and models. High-resolution application of seismic has a central role in the identification and characterization of seismotectonic and seismogenetic zones and of the related capable faults. The earthquakes represent an important external risk for key constructions and nuclear power plants and capable faults cause near-surface displacements being considered to be the more critical for site safety. A close cooperation among geophysicists, geologists and seismologists is recommended in the hazards evaluation, alike in macrozoning for location of seismic sources and in microzoning for the measure of terrains mechanical properties and dy