1,721,121 research outputs found
The combined interpretation of vertical electric and magnetotelluric soundings: a case history
No full textA case history in which magnetotelluric (MT) soundings and Vertical Electric Soundings (VES) were performed on a structurally simple geology is presented. The comparison of MT synthetic apparent resistivity curves, computed using the one-dimensional model parameters derived from VES interpretation, with the experimental ones, is discussed. Inversion of MT data gives a range of oscillation for model parameters which is conditioned by data scattering. A careful assessment of the inversion effectiveness, by means of suitable statistical tests, allows us to single out the most statistically reliable model parameters. -Author
Un semplice esperimento sulla propagazione delle onde elettromagnetiche nei mezzi materiali. Proposta d'un'esposizione didattica.
No full textEsperimento di propagazione delle onde e.m. in mezzi materiali, riproducibile per la didattica nella scuola secondari
Indagini preliminari: prospezione geofisica
No full textLo scavo archeologico può essere utilmente indirizzato dai risultati di indagini geofisiche di superficie. Queste indagini si fondano sulla differenziazione di alcune proprietà fisiche tra il materiale archeologico ed il terreno ospitante. Le più comunemente utilizzate sono la suscettività magnetica, la resistività elettrica e la permittività dielettrica. La prima è legata alla presenza di frammenti di minerali magnetizzati, la seconda alla diversa attitudine dei terreni
e dei materiali archeologici alla conduzione della corrente elettrica, la terza alla velocità di propagazione delle onde elettromagnetiche, che si riflettono sulle superfici di discontinuità. Alcuni esempi illustrano le modalità delle diverse indagini e l’efficacia dei rispettivi risultati.The archaeological excavation can be usefully addressed by the results of surface geophysical investigations. These investigations are based on the diff erentiation of some physical properties of the archaeological material and host soil. Th e most commonly used are the magnetic susceptibility, electrical resistivity and dielectric permittivity. Th e fi rst is related to the presence of magnetized mineral fragments, the second to the diff erent attitude of terrains and archaeological materials to conduction of the electric current, the third to the speed of propagation of electromagnetic waves, which are refl ected at the surfaces of discontinuity. Some examples illustrate how the various investigations are carried out and the eff ectiveness of their results
Caratterizzazione di ambienti tettonici appenninici mediante indagini magnetotelluriche (Valle del Trigno)
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A new attempt at automatic data processing in Magnetotellurics
No full textConsidering the magnetotelluric (MT) signal in its physical reality as a stochastic process, we present here a new methodology for the search and analysis of the wave packets which are most compatible with theoretical calculation requirements. In adapting the length of the physical data blocks to a small number of oscillations of the signal, we are able to identify those data ensembles which show particularly high rotated coherence values (higher than 0.9). An example of such calculations is supplied by means of the analysis of an MT sounding which demonstrates the validity of this procedure. © 1979
The characterisation of aquifers by means of resistivity investigations
No full textThe present paper contains the description of data collection and the main results that were achieved in the frame of the CAMI project using resistivity-based methods. In particular the Electrical Resistivity Tomography (ERT) was used to get detailed 2D and 3D resistivity models of the shallowest part of the subsurface in the test area (down to some decades of metres), while to reach the whole designed investigation depth Magnetotellurics (MT) and “Time-Domain ElectroMagnetic method” (TDEM) were used and their costs-to benefits ratios were evaluated. As far as the results of the resistivity investigation are concerned, a reliable 4D model of the resistivity distribution down to more than 500 m b.g.l. was obtained by TDEM data inversion. This model showed variations of the resistivity vs time of the first confined aquifer which were in excellent agreement with direct data. A reliable estimation of the effective porosity was also obtained for the same aquifer. Finally an important fresh water aquifer was found at depth, which was then reached and characterised by a purposely drilled hole
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