How Close are the Edges of a Closed Fracture?

A laboratory experiment is peresented where the theory of amplitude reflection tuning in thin beds is tested. The results show a very good agreement with the theory previsio

Magnetic, electrical, and GPR waterborne surveys of moraine deposits beneath a lake: A case history from Turin, Italy

Bathymetry and bottom sediment types of inland water basins provide meaningful information to estimate water reserves and possible connections between surface and groundwater. Waterborne geophysical surveys can be used to obtain several independent physical parameters to study the sediments. We explored the possibilities of retrieving information on both shallow and deep geological structures beneath a morainic lake by means of waterborne nonseismic methods. In this respect, we discuss simultaneous magnetic, electrical, and groundpenetrating radar (GPR) waterborne surveys on the Candia morainic lake in northerly Turin (Italy).We used waterborne GPR to obtain information on the bottom sediment and the bathymetry needed to constrain the magnetic and electrical inversions. We obtained a map of the total magnetic field (TMF) over the lake from which we computed a 2D constrained compact magnetic inversion for selected profiles, along with a laterally constrained inversion for one electrical profile. The magnetic survey detected some deep anomalous bodies within the subbottom moraine. The electrical profiles gave information on the more superficial layer of bottom sediments. We identify where the coarse morainic material outcrops from the bottom finer sediments from a correspondence between high GPR reflectivity, resistivity, and magnetic anomalie

Micro-geophysics to assess the integrity of some statues in the Museo Egizio of Turin, Italy

On request of the Soprintendenza in charge of the Museo Egizio of Turin, a quite large number of tests have been performed on four statues of the museum to assess their integrity both for practical (moving the statue) and archaeological purposes. Ultrasonic tomography and georadar have been used with fine results on sub-decimeter scale. In this paper we present the main results on the statues of the Pharaons Ramses II (Fig.1 left) and Tuthmosis I. (Fig.2 left). Both the statues belong to the collection set up by Bernardino Drovetti, Console Generale of France in Egypt in the early XIX century. Ramses II statue was restored in the first half of the XIX century. Few documents can be found on these restoration works: very likely the statue arrived broken to Turin and was reassembled with cement mortar (Hartleben, 1909) No news can be found neither on the type of mortar nor on the quantity of mortar actually used. The statue of Ramses was probably found at Tebe in 1818. It is made by basanite exploited from a quarry in Uadi Hammamat. The basanite is a basaltic extrusive rock also known as Lydian stone or lydite. It was almost exclusively reserved to the crafting of statues of pharaons or divinities. In many parts of the statue the mortar (as dark as the stone) is clearly visible (Fig.1 right). The statue of Tutmosis I was found by J.J. Rifaud , a Drovetti 's agent, in 1818 in Tebe, very likely in the Karnak temple. The king sits on a throne with many scripts on both the sides of the seat. The statue is made by a dark diorite with some light pink plagioclase crystals sizing few centimeters. Its conservation seems fairly goo

2D and 3D data processing of archaeo-magnetic data

Introduction. The Sabine Necropolis at Colle del Forno (700-300 B.C.) at Montelibretti, Rome is characterized by dromos chamber tombs, most of them unexplored till now. The tombs can be assimilated to cavities of a standard volume of some cubic meters; the entrance of the tombs is a corridor 6 m long with a 1 square meter section . The surficial geology of the area consists of a series of tuffs about 10 m thick overlying Pleistocene-Quaternary sandy-clayey sediments. A thin layer of top soil (20 - 30 cm) covers the tuff. The investigation of the Necropolis in the past decade has been performed by different geophysical methodologies: electrical, electromagnetic and magnetic methods have been widely adopted to investigate several chamber tombs (Piro et al, 2001). The aim of this paper is to analyze an integrated approach to the processing of magnetic survey data. The magnetic susceptibility contrast between topsoil, subsoil and rocks (topsoil is normally more magnetic than subsoil) permits to detect ditches, pits and other silted-up features that were excavated and then silted or back-filled with topsoil. Meanwhile back-filled areas produce positive anomalies, less magnetic material introduced into topsoil, including many kinds of masonry (for example, limestone walls) may produce negative anomalies of the order of some nanoteslas. The same behavior is related to the presence of cultural voids and tombs whose magnetic anomaly is generated by the lack of magnetic materials due to the cavities of the tombs. In the area a diffused magnetisation is manly due to the presence of top soil and tuff materials and high negative susceptibility contrasts can be expected because of the presence of the tombs. The magnetic survey was performed along a regular grid of 0.5 m x 0.5 m using a optical pumped Caesium-vapour magnetometer G858 (Geometrics), in the gradient configuration, on an area which is well known as far as the presence, size and position of tombs are concerne

Application and comparison of three tomographic techniques for detection of decay in trees

This paper reports application of electric, ultrasonic, and georadar tomography for detection of decay in trees and their comparison with the traditional penetrometer. Their feasibility in arboriculture is also evaluated, critically considering some "open problems." The experiments were carried out in an urban environment on two plane (Platanus hybrida Brot.) trees. Both trees, after felling, showed extensive white rot in the central cylinder. The electric tomography revealed low resistivity zones roughly centered in the trunk. A comparison with the successively cut sections showed a fine correspondence to decayed areas and a strong correspondence between high moisture zones and low resistivity zones. Ultrasonic tomography demonstrated to be a very effective tool for the detection of internal decay, accurately locating the position of the anomalies and estimating their size, shape, and characteristic in terms of mechanical properties. With the georadar technique, the high contrast of electromagnetic impedance measured between the inner decayed section and the outside sound section allowed the detection of the interface between the sound and decayed section of the tree, using radar acquisition in reflection modality. The penetrometer profiles detected the low-resistance areas inside the two trunk

Geoelectrical measurements for agricultural canal seepage detection

The protection of water resources is a current problem at a global scale, especially in regions where this resource is poorly available. In this respect there is an increased pressure on water managers to improve water use efficiency. The use of geophysical tests as a tool for managing the efficiency of irrigation networks is well documented in literature since they have an high potential for canal seepage identification and quantification. In this respect, the present study is focused on the use of electrical resistivity methods on some sample canals of the Piedmont Region network. The results obtained have underlined the usefulness of geophysical methods in detecting local anomalies in the lining, potentially related to seepage losses, by means of waterborne CVES and in imaging the passage of saline tracer tests plumes, to be used for a quantification of the seepage losses, using cross-flow high-speed ERT

Case study: A GPR survey on a morainic lake in northern Italy for bathymetry, water volume and sediment characterization

We carried out an extensive waterborne GPR survey consisting of 50 profiles with a total length of nearly 37 km on the morainic lake of Candia northerly Turin (Italy). Our aim was to test the capability of GPR to estimate the bathymetry, the water volume and the sediment type. We enhanced and controlled the GPR data processing and interpretation with bathymetry acquired with an acoustic echo sounder and measured conductivity and temperature profile of the water column with a multiparametric probe. We also analyzed the diffraction hyperbola that originated within the sediments in order to estimate the velocity and relative permittivity. With the permittivity and dielectric mixing rules, we estimated the porosity of the sediments above the diffracting objects and drew a map of the bottom lake porosity

Waterborne GPR survey for estimating bottom-sediment variability: A survey on the Po River, Turin, Italy

We conducted an integrated geophysical survey on a stretch of the river Po in order to check the GPR ability to discriminate the variability of riverbed sediments through an analysis of the bottom reflection amplitudes. We conducted continuous profiles with a 200-MHzGPR system and a handheld broadband EM sensor.Aconductivity meter and a TDR provided punctual measurements of water conductivity, permittivity, and temperature. The processing and interpretation of the GEM-2 and GPR data were enhanced by reciprocal results and by integration with the punctual measurements of the EM properties of the water. We used a processing flow that improved the radargram images and preserved the amplitude ratios among the different profiles and the frequency content at the bottom reflection signal.We derived the water attenuation coefficient both from the punctual measurements using the Maxwell formulas and from the interpretation of the GPR data, finding an optimal matching between the two values. The GPR measurements provided maps of the bathymetry and of the bottom reflection amplitude. The high reflectivity of the riverbed, derived from the GPR interpretation, agreed with the results of the direct sampling campaign that followed the geophysical survey. The variability of the bottom-reflection-amplitudes map, which was not confirmed by the direct sampling, could also have been caused by scattering phenomena due to the riverbed clasts which are dimensionally comparable to the wavelength of the radar pulse