Ahmad Ghorbani

RÉSUMÉ — Les résultats obtenus sur des échantillons de sols arides iraniens soumis à des paliers de contraintes de 24,43 kPa à 195,4 kPa ont montré que la résistivité augmentait avec le chargement oedométrique. Ce phénomène qui n'est pas observé sur des sols tempérés a été interprété comme le résultat d'une cristallisation des sels évaporitiques présents dans les solutions interstitielles. ABSTRACT — Results obtained from samples of arid soils from Iran submitted to vertical stresses in the range of 24,43 kPa to 195,4 kPa have shown that resistivity increased during the oedometric loading. This phenomenon which is not observed from soils taken from areas of moderate climate was interpreted as a result of the crystallization of evaporite salts existing in the soil pore solutions.

ABSTRACT The aim of this paper is to show complementarity of temporal and spectral induced polarization, applied to ore body detection and differenciation. Study had been lead into well known geological background through borings, geochemical measurements, and also through some electrical resistivity tomographies. Temporal induced polarization (TIP) material and carry out: TIP had been carried out in a quite original way by employed device, and technique. Measurements had been done with SYSCAL PRO (Iris Instrument, Ltd.) transformed into ELREC PRO: this make it possible to differenciate transmitter device (with VIP generator manufactured by IRIS) from receiver one. The main interests are (i) to avoid internal coupling effects and between transmittor/receptor cables on soil, and (ii) to obtain higher electrical power (until 3000 watt) necessary to reach 30-40m depth. Voltage measurement is done through non-polarizable electrodes. Electrical chargeability and resistivity tomographies had been obtained by lateral device displacement. Pole-dipole device had been chosen because it is the best compromise between minimizing coupling effects, getting enough power to reach wanted depth, and necessary lateral resolution. Spectral induced polarization (SIP) material and carry out : SIP FUCHS II device (manufactured by Radic Research) had been used. As the device is not configurated into a multielectrode way, and as one sounding is very time consuming (about 7 hours), only 2 soundings had been done, located on major chargeability anomalies. First results: A a first analysis, a 3 lauer model can be observed: very resistivive level between 0 and 5m depth (up to 1000 ohm.m), more conductive between 5 and 20-25m depth (50 ohm.m), and finally an increasing resistivity. A finer analysis indicates some big conductive zone 50m wide (50 ohm.m) from surface until 30m depth. This could be exlplained by clay or ore body presence. Chargeability analysis indicate us values very high chargeabilities at resistivity anomaly zone (up to 80 mV/V), whereas everywhere else these values are less than 10mV/V. Such chargeability intensity may only be explained by ore body presence. At this stage we could think that there is only one kind of ore body (nevertheless geochemical analysis indicate 2 different types). Two SIP soundings had been done vertically to chargeability anomalies. There is no difference for resistivity values, but phase diagrams are very different (maximum phase is 3 Hz for one sounding and less than 0.1 Hz for the second). Some SIP modelling is now to be done to better characterize ore body nature. As a conclusion, the measurements of electrical resistivity, of chargeabilité and PPS are very complementary (fastness for the chargeability / strong capacity of differenciation for SIP).

Potential field images that are obtained in potential field methods (Gravity, Magnetic) are used worldwide as part of exploration programs for mineral resources. These images consist of different anomalies which in many cases are coated with noises. In order to extraction details of these images and enhancing their features, filtering techniques are applied. In this process more effort is balance between signals and noises in filtered images. When data quality permits a range of high-pass filters, such as upward continuation and vertical derivative, can be used to bring out fine details. However, since they are a form of high-pass filter they also have an undesirable property of enhancing noise. Other applied filters are local phase filters such as tilt angle filter and theta filter which fundamentally of these filters are local phase measuring of the potential field data over images. The tilt angle is ratio of the vertical derivative to absolute amplitude of the total horizontal derivative. The tilt angle is positive when over the causative body, zero near body edges and negative outside the body. Advantages of this filter are possibility of comparison between its results to derivative-based filters, its dimensionless nature and simple interpretation rather than analytic signal. Disadvantage of this filter is encountering with deep sources the detected edge is blurred as form of hallo. For overcome this problem such new tilt inferred filters namely total horizontal derivative of tilt angle (THDR), 2-order vertical derivative of tilt angle, normalized total horizontal derivative (NTHD) are introduced which produce more improvement results. These filters produce useful information in both deep and shallow sources. Furthermore these filters act as a method to separate regional anomalies from residual anomalies. In this work we applied these filters on synthetic gravity data and on real aeromagnetic data from Abadeh quadrangle in Iran. This region has been located in 55° 35' longitudes and 32° 31' latitude. The main structure in this area is Dehshir-Baft fault with NW-SE trend which separates Shirkooh granite in northeast from Abarkooh plain in center. Other magnetic anomaly source is ophiolite outcrop in southeast. With application of these fitters the main geological and structural features such as basic lava in south, ophiolite outcrops in southeast and main fault with NE_SW in northeast have been enhanced. Keywords: Potential field, Signal, High-pass filter, Derivative-based filter, Local-phase filter, Tilt angle, THDR, NTHD

... saturation-desaturation cycles: testing a new laboratory set-up. A. Maineult, A. Ghorbani, S. Leder, K. Mahiouz and M. Zamora Institut de Physique du Globe de Paris, CNRS et Université Paris VII Denis-Diderot, France (maineult@ipgp.fr, +33 (0)1 44 27 49 38) ...

The low-frequency conductivity response of water-saturated packs of glass beads reflects a combination of two processes. One process corresponds to the polarization of the mineral/water interface coating the surface of the grains. The other process corresponds to the Maxwell-Wagner polarization associated with accumulation of the electrical charges in the pore space of the composite medium. A model of low-frequency conductivity dispersion is proposed. This model is connected to a triple-layer model of electrochemical processes occurring at the surface of silica. This model accounts for the partition of the counterions between the Stern and the diffuse layers. The polarization of the mineral/water interface is modeled by the electrochemical polarization model of Schurr for a spherical grain. We take into account also the DC surface conductivity contribution of protons of the sorbed water and the contribution of the diffuse layer. At the scale of a macroscopic representative elementary volume of the porous material, the electrochemical polarization of a single grain is convoluted with the grain size distribution of the porous material. Finally, the Maxwell-Wagner polarization is modeled using the complex conductivity of a granular porous medium obtained from the differential effective medium theory. The predictions of this model agree well with experimental data of spectral induced polarization. Two peaks are observed at low frequencies in the spectrum of the phase. The first peak corresponds to the distribution of the size of the beads and the second peak is due to the roughness of the grains.

When used for archaeological purposes, geophysical methods are often useful for the exploration, detection and mapping of archaeological remains. In the case of ancient metallurgical activities, slag accumulations form precious mineral records of these activities. Evaluating the volume of slag produced in such locations is an important issue, since it enables an estimate of the amount of metal produced in

Spectral-induced polarization (SIP) is widely used for environmental and engineering geophysical prospecting and hydrogeophysics, but one major limitation concerns the electromagnetic (EM) coupling effect. The phase angles related to EM coupling may increase even at frequencies as low as 1 Hz, depending on the ground resistivity, the array type, and the geometry. Most efforts to understand and quantify the EM coupling problem (e.g., theory and computer codes) have been developed for dipole-dipole arrays. However, we used a Schlumberger array to acquire SIP data. We found that with this array, the use of an appropriate cable arrangement during data acquisition can reduce EM coupling effects in the same proportion as for the use of a dipole-dipole array, which is the pure response of the studied earth. To measure the influence of the cable layout, four cable configurations with the same electrode spacing were compared for modeling and experimental data. We discovered that the classica...

Seven well-characterized clay-rocks have been taken from three test sites to perform spectral induced polarization (SIP) measurements during desiccation of these samples. These test sites include (1) the Tournemire site (IRSN) located in south of France,(2) The Bure test site (ANDRA) located in west of France, and (3) the Super-Sauze earthflow located in south western of France. We dried the samples at ambient temperature followed by heating between 65° C and 105° C. The quadrature conductivity, at very low-frequency, ...

Page 1. THESE DE DOCTORAT DE L'UNIVERSITE PIERRE ET MARIE CURIE Spécialité : Géophysique Appliquée Pour obtenir le grade de DOCTEUR de L'UNIVERSITE PIERRE ET MARIE CURIE (PARIS 6) Sujet de la thèse : Contribution au développement de la ...