Searching for buried metallic evidence at crime scenes or at potential disposal sites can be a daunting task for forensic personnel. In particular, it is common to search for a small firearm that was discarded or buried by the perpetrator. When performing forensic searches, it is recommended to first use non-invasive methods such as geophysical instruments to minimize damage to evidence and to the crime scene. Geophysical tools are used to pinpoint small areas of interest across a scene that will be invasively tested later. Prior to this project, there was no published research that tested the utility of the conductivity meter to search for metallic weapons such as firearms and blunt or sharp edged weapons. A sample comprised of 32 metallic weapons was buried in a controlled setting to test the applicability of a conductivity meter for forensic searches. Weapons were tested at multiple depths; once data collection was performed for one depth, the weapons were reburied 5cm deeper until they were no longer detected. Results obtained with conductivity meter were compared to results obtained by the ground-penetrating radar using different depths and transect intervals. The effects of several variables on detection such as weapon size, metallic composition, burial depth, and transect interval were analyzed in order to explore the limitations of each instrument. Results obtained from this controlled research can provide guidelines to help law enforcement in real-world searches.

No description available.

Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Science. / Microfiche copy available in Archives and Science. / Bibliography: leaves 230-233. / Ph.D.

Velocity anisotropy is present at a point in a medium if the seismic velocity in one direction in general differs from that in another direction. The problems associated with the determination of subsurface velocity in anisotropic media by the use of surface seismic reflection data are analyzed. Previous studies of anisotropy in exploration seismology required bore-hole data as well as surface data to detect the presence of velocity anisotropy. Three special types of wave propagation are of interest in reflection seismology, in addition to the general case. The theory of isotropic media is commonly utilized in exploration seismology. Elliptical anisotropy has been the method for handling anisotropic media in the past. The theory of transversely isotropic media is studied in detail since this is a reasonable anisotropy model for exploration use. Layered periodic isotropic structures are considered because of the relationships between the elastic coefficients that yield transverse isotropy in the limiting case for which the isotropic lavers are thin in comparison to the wavelength of a propagating disturbance. Synthetic common-depth-point reflection seismic traces were generated for a uniformly anisotropic halfspace, a model with seismic velocity increasing linearly with depth, velocity increasing stepwise with depth, a buried anisotropic interval in an otherwise isotropic section, and models characterized by the dip varying continuously with depth. Correlation methods (velocity analysis) are developed for the determination of rms velocity vs. two-way reflection time for both isotropic and anisotropic (transversely isotropic) media. These methods are applied to the models discussed above for varying amounts of anisotropy for each model. When the surfaces defined by the velocity analysis correlation matrices are integrated to determine the volume under the surface, it is possible to determine within about one percent the degree of anisotropy in a uniformly anisotropic medium. In a medium of varying anisotropy, it does not appear possible to obtain the same degree of accuracy as for the uniform case. Two isotropic dipping layer models were studied to determine the effects of dip on velocity analysis. The effects of dip are such that the analysis methods yield erroneous results for dips in excess of about 10-12 degrees for the models studied. Random noise degrades the velocity analysis (i.e., the magnitudes of the correlation peaks), but does not affect the accuracy of the results. Lateral velocity gradients appear to have no discernible effects on a velocity analysis for the models studied. Results of this study indicate that the compressional wave data normally used in reflection seismic work may not be useful for the detection of velocity anisotropy. Shear wave (SV) data, on the other hand, are ideally suited to this purpose. Hmvever, the necessity of shear wave data for the detection of anisotropy may limit these methods strictly to land use. This study indicates that the probability of detecting anisotropy by using surface methods is sufficiently high to warrant field testing. / Ph. D.

Yes / The slag pit furnace of the Trøndelag tradition for iron production is a very specific cultural-historical tradition in central Norway in the Early Iron Age, but few of these iron production sites have been excavated in their entirety and there is therefore a lack of information about their size, spatial layout and organisation in the landscape. The aim of this paper is therefore to investigate how magnetic geophysical methods can be used as a way of locating, delimiting and characterising activity zones and specific archaeological features associated with this tradition of iron production. The NTNU University Museum in Trondheim performed geophysical surveys of four different iron production sites, combining topsoil volume magnetic susceptibility measurements and detailed fluxgate gradiometer surveys. Analysing and comparing the survey results with sketches and topographic survey results, as well as comparable geophysical survey data from iron production sites elsewhere in Norway, made it possible to gain new and valuable cultural-historical and methodological knowledge. The topsoil volume susceptibility measurements revealed a strong contrast between the main production areas and the natural background measurement values, often in the range of 7–27 times the median background values. The absolute highest measured values were usually in the area closest to the furnaces, and within the slag mounds. Satellites of high readings could be interpreted as roasting sites for iron ore, and even areas with known building remains related to the iron production sites had readings stronger than the median. The fluxgate gradiometer data helped to characterise individual features further, with strong geophysical contrast between features within the iron production sites and the areas surrounding them. Also, by analysing their physical placement, geophysical characteristics such as contrast, magnetic remanence and size, it was possible to gain further insight into the spatial organisation by indicating the potential location of furnaces, the spread of slag and the handling of iron ore. The latter involved both where the roasted iron ore was stored and where it was roasted. The geophysical characteristics of the furnaces were less uniform than situations reported elsewhere in Norway, which can be explained by the reuse of furnaces and slag pits. The spread of highly remanent material in and around the furnaces and elsewhere within the limits of the iron production sites also created a disturbed magnetic picture rendering it difficult to provide an unambiguous archaeological interpretation of all the geophysical anomalies identified. In conclusion, these results showed that the geophysical methods applied made it possible to indicate the physical size, layout and internal spatial organisation of iron production sites of the Trøndelag slag pit furnace tradition.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2016. / The Jacomynspan Ni-Cu sulphide mineralisation is hosted within a 100m thick steeply dipping tabular, differentiated, sill of mafic to ultramafic composition intruded into country gneissic rocks of the Namaqualand Metamorphic complex. This sill is predominantly composed of tremolite schist (metamorphosed pyroxenite) containing lenticular bodies of harzburgite. The harzburgite generally hosts net-textured mineralisation with up to 50% by volume of the rock. Massive sulphide veins and stringers are occasionally present within the harzburgite. The sulphide minerals are a typical magmatic assemblage of pyrrhotite, chalcopyrite and pentlandite. The sill covers an approximate strike length of about 5km but only a small portion covering 1km x 1km was selected for this study. Physical property studies carried out on the drill core (magnetic susceptibility and conductivity) indicate that the country gneissic rocks are not conductive and neither are they magnetically susceptible. However, the mineralized sill has elevated values of both magnetic susceptibility and relative conductivity compared to its host making it a suitable target for both magnetic and electromagnetic inversion. Drilling done so far on the study area has shown that the well-mineralised harzburgite (hosted within the poorly mineralised ultramafic sill) is not a continuous body but occurs in ‘pockets’. There is therefore need to use the available geophysical and geological datasets to derive a model of these well mineralised pods. This study is therefore intended to assess the feasibility of using electromagnetic (EM) methods together with other geophysical methods and geology in obtaining a model of the harzburgite pods hosted within the less conductive poorly mineralised ultramafic sill in order to guide further drilling. Geosoft’s VOXI Earth Modelling software was used to model the high resolution airborne magnetic data for this study. Cooper’s Mag2dc (www.wits.ac.za) and Stettler’s Magmodintrp software (personal communication, 2015) was also used during modelling of the magnetic data to compliment the modelling from VOXI. The mineralised ultramafic sill was clearly mapped in both the 3D model representation from Mag2dc modelling and VOXI’s 3D unconstrained smooth model inversion for the study area. Based on the physical properties studies carried out on the study area, EM data (both ground and downhole EM) were modelled using Maxwell software. The poorly mineralised tremolite schist was clearly modelled. In order to better constrain the targets, an assumption was made that at late decay times the currents would be focused in the centre of the large EM plate probably giving an indication of the most conductive part of the intrusion. Smaller ‘Resultant EM plates’ of dimensions, 300mx300m that coincide with the centre of the large EM plates (with a conductance above 100S) were constructed in iv Maxwell software and integrated with the DXF file of the Micromine geology model of the well mineralised harzburgite clearly mapping the well-mineralised harzburgite and showing its possible extensions. 2D inversion modelling was conducted on all audio-frequency magnetotelluric (AMT) data for this study area. The modelling results clearly mapped the mineralised intrusion.

Submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg as a requirement for the Degree of Master of Science. Johannesburg, 1992. / The effect of sodium on clays dominates the formation and ecology of granitic eatenas in the Eastern Transvaal Lowveld. This study reviews the process involved and explains the soil, vegetation and erosion patterns in this landscape. Weathering parent rock gives rise to sodium in sufficient amounts to promote clay dispersion. Dispersed, mobile, clays respond to seasonal pulses of laterally moving soil water resulting in alternating zones of clay illuviation and clay deposition down hillslopes [Abbreviated Abstract. Open document to view full version] / AC2017

La détection de cavités en milieu urbain est importante pour prévenir différentes causes d'accidents liés à des possibles effondrements. Les cavités sont aussi des cibles d'intérêts pour les archéologues, car les cavités oubliées sont de potentielles sources de matériel révélant des usages passés. Ces cavités sont de tailles différentes, d'origine anthropique ou non, en milieu extérieur ou sous des bâtiments. Leur taille, ainsi que les propriétés physiques du milieu extérieur dans lequel elles se situent, permettent l'utilisation de différentes méthodes géophysiques. Nous nous sommes concentrés sur l'utilisation de deux méthodes géophysiques, le radar de sol et la tomographie par mesures de résistivité électrique, pour localiser et déterminer les cavités métriques à sub-métrique dans le proche sous-sol (6 premiers mètres). Les mesures de radar de sol sont sensibles aux variations de permittivité diélectrique entre la cavité et le milieu extérieur. Nous montrons par des modélisations numériques un effet sur l'amplitude de la réfléchie en fonction du déport qui permet de discriminer entre une cavité vide et une cavité pleine d'eau. Nous étudions aussi l'amplitude de la réfléchie à incidence normale sur le toit d'une cavité à section carrée en fonction de sa profondeur et de sa taille. Nous mettons en évidence une relation logarithmique profondeur versus taille de cavité pour laquelle l'amplitude de la réfléchie est maximum pour les fréquences de prospection typiques du radar de sol. Par ailleurs nous confirmons qu'alors que les mesures radar permettent de déterminer avec précision les dimensions d'une anomalie dans un sous-sol homogène et peu conducteur, les mesures de résistivité électrique permettent elles de déterminer des zones de hautes résistivités à l'emplacement des cavités. Nous couplons ces deux méthodes géophysiques dans deux études de cas, en utilisant la profondeur des interfaces déterminées sur des radargrammes pour contraindre les modèles de résistivité inversés par l'ajout d'information a priori. / The detection of cavities in urban areas is important to prevent different causes of accidents related to possible collapse. The cavities are also interesting targets to archaeologists because forgotten cavities are potential sources of material revealing past uses. These cavities are of different sizes, of anthropogenic origin or not, in an outdoor setting or under buildings. Their size and the physical properties of the external environment in which they are located, allow the use of different geophysical methods. We focused on the use of two of them, Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT), to locate and determine cavities in the near subsurface (first 6 meters). GPR data are sensitive to variations in dielectric permittivity between the cavity and the external environment. We show by numerical modelling an effect on the amplitude of the reflected signal depending on the offset which could enable discrimination between an empty cavity and a cavity filled with water. We also study the amplitude of the reflected wave at normal incidence on the roof of a cavity of square cross section in terms of its depth and size. We show a logarithmic relationship between the cavity size and its depth at which the amplitude of the reflection is maximum for frequencies of typical exploration with GPR. Furthermore, we confirm that while GPR data determine accurately the size of an anomaly in homogeneous low conductive medium, ERT helps to determine areas with high resistivity at the location of cavities. We combine these two geophysical methods in two case studies, using the depth of interfaces detected on radargrams as a priori information to constrain the inversion of electrical resistivity models.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Devido a sua grande extensão latitudinal, a costa brasileira é influenciada por diferentes regimes climáticos e oceanográficos. Adicionalmente, a distribuição da população brasileira é caracterizada por uma alta concentração nas capitais litorâneas. Todos esses fatores levam à construção de inúmeras estruturas de engenharia que podem de alguma forma impactar o transporte de sedimento e consequentemente o balanço sedimentar de algumas praias. Uma das formas mais eficientes de recuperar esse balanço sedimentar é a alimentação artificial de praias, com sedimentos provenientes da plataforma continental com características semelhantes. Os métodos geofísicos acústicos permitem mapear de forma eficiente o fundo e o subfundo marinho para a busca de áreas fontes para a lavra de forma eficiente. O objetivo deste estudo é a identificação de padrões geoacústicos a partir de analises quantitativas e qualitativas, para a caracterização de áreas fontes de areias siliciclásticas compatíveis com sedimentos de praias em erosão na cidade do Rio de Janeiro. O mapeamento foi realizado na plataforma continental interna do Rio de Janeiro, em área adjacente à praia de Itaipuaçu (Maricá, RJ). As análises evidenciaram depósitos, localizados entre 19 e 30 metros, de areias com granulometria, textura e selecionamento em condições ideias para a recomposição de praias do Rio de Janeiro. / The Brazilian coast is afected by different oceanographic characteristics, mainly due to its large latitudinal extention. Additionally, the distribution of the Brazilian population is characterized by a high concentration in the coastal capital. These facts generate a large number of coastal engineering structures that may impact the sediment transport and consequently the sediment balance in some beaches. All these factors impact some sand beaches and the best choice for its mitigation and recovering is the beach nourishment - with sediments from the continental shelf with similar characteristics. However to find a good place for dredging in the shelf, we need to use geophysical methods that allow to map the bottom and sub bottom environments more efficiently. The objective of this study is the identification of geoacoustics patterns, following qualitative and quantitative analyzes, for characterizing source areas of siliciclastic sands in ideal conditions for recovering eroded beaches in Rio de Janeiro. The mapping was done in the shelf in front of Itaipuaçu beach (Maricá, RJ). The quantitative results showed well sorted median sand placers seaward of the closure depth, located between 19 and 30 meters, ideal for Rios beaches recovering.

The use of geophysical testing methods has considerable potential to be a cost effective and accurate technique to assess near-surface soil conditions. Multi channel analysis of surface waves (MASW) test is a geophysical non-intrusive test that uses the dispersive characteristic of Rayleigh waves to estimate low strain shear modulus and damping coefficient of near-surface soil. Also, this technique is used to detect underground voids. Recently, MASW technique has gained more attention, partly because of its ease of use and partly because of the significant improvements in data acquisition systems. The theories of MASW test consider the effect of horizontal soil layering, though the effect of lateral inhomogeneities (i. e. cavities and voids), inclined layering and inverse layering (i. e. a layered system in which the top layers are stiffer than the bottom ones) are not addressed properly in these theories. <br /><br /> The objective of this dissertation is to investigate the effect of lateral inhomogeneities on the propagation of Rayleigh waves in an elastic half-space excited by a transient loading. The results can be applied to locate underground cavities using MASW test and to improve the MASW analysis techniques. In lieu of theoretical solutions, two and three dimensional numerical models are constructed to simulate the MASW test. To assure the quality of the obtained data, numerical models are calibrated with Lamb solution. Voids with different sizes and embedment depths are inserted in the medium. Responses along the surface as well as inside the medium are recorded and analyzed in time, frequency, spatial and frequency-wave number domains. Different material types and sources are used to generalize the results. Afterwards, the combined effect of void and layered systems on the surface responses are studied. To verify the results, experimental field and laboratory data are presented and the trends are compared to the numerical results. <br /><br /> It is found that the void starts to vibrate in response to the Rayleigh wave excitation. Due to the vibration of the void energy partitioning occurs. Part of the incident energy is reflected in the form of Rayleigh wave. Another part is converted to body waves, and spread into the medium. The transferred part of the energy is attenuated and has smaller amplitudes. Finally, a part of energy is trapped in the void region and bounces back and forth between the void boundaries, until it damps. The trapped energy is associated to higher modes of Rayleigh waves and excited Lamb waves. The effect of trapped energy is seen as a region in the vicinity of the void with concentrated energy, in frequency domain. The extents of this region depends on the void size, and the frequency content of the incident energy. Thus, in some cases it is possible to correspond the size of the model to the extents of the region with energy concentration. <br /><br /> A new technique is proposed to determine the location of a void, and estimate its embedment depth. The technique is called Attenuation Analysis of Rayleigh Waves (AARW), and is based on the observed damping effect of the void on the surface responses. For verification, the results are compared to experimental field and laboratory data. The observations are in good agreement with the observed numerical results. Further, the AARW technique showed to be a promising tool for void detection.