RESUMEN

One of the most complex challenges of heritage sciences is the identification and protection of buried archaeological heritage in urban areas and the need to manage, maintain and inspect underground services. Archaeology and geophysics, used in an integrated way, provide an important contribution to open new perspectives in understanding both the history of cities and in helping the decision makers in planning and governing the urban development and management. The problems of identification and interpretation of geophysical features in urban subsoil make it necessary to develop ad hoc procedures to be implemented and validated in significant case studies. This paper deals with the results of an interdisciplinary project in Cusco (Peru), the capital of Inca Empire, where the georadar method was applied for the first time in the main square. The georadar method was successfully employed based on knowledge of the historical evolution of Cusco and the availability of archaeological records provided by some excavations nearby the study area. Starting from a model for the electromagnetic wave reflection from archaeological structures and pipes, georadar results were interpreted by means of comparative morphological analysis of high amplitude values observed from time slices with reflectors visualized in the radargrams.

RESUMEN

There is an increasing interest in the application of geophysical surveys to assess the soil water content (SWC) variation in both spatial and temporal scales. In this work, a geophysical survey was carried out at an experimental farm in dry and wet conditions. We determined the SWC data measured with the gravimetric method, apparent electrical conductivity by electromagnetic induction (EMI) and amplitude of Ground Penetrating Radar (GPR) data at different frequencies. Geophysical sensors are an efficient tool for soil mapping at high resolution; however; there is a need to improve the knowledge on their capabilities and limitations under field conditions, especially for GPR. The geophysical survey provides an example of the application of these techniques to evaluate the spatial variability of SWC in two different water conditions. The contribution of geophysical data in understanding the spatial variability of SWC was investigated applying both the traditional analysis and spatial techniques. The results indicated that the geophysical data captured the spatial variation of SWC in non-invasively way especially in dry condition. However, they also showed the complex interplay between factors controlling SWC and geophysical responses and the drawbacks of geophysical sensors under inhomogeneous water conditions. Our findings also highlighted that EMI survey provides the potential to map the SWC variability within a relatively short time. The results obtained in this research are important from the agronomical viewpoint, since they allow increasing efficiency of irrigation practices, which is important in times characterized by climate change.

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RESUMEN

There is an increasing interest in the application of geophysical surveys to assess the soil water content (SWC) variation in both spatial and temporal scales. In this work, a geophysical survey was carried out at an experimental farm in dry and wet conditions. We determined the SWC data measured with the gravimetric method, apparent electrical conductivity by electromagnetic induction (EMI) and amplitude of Ground Penetrating Radar (GPR) data at different frequencies. Geophysical sensors are an efficient tool for soil mapping at high resolution; however; there is a need to improve the knowledge on their capabilities and limitations under field conditions, especially for GPR. The geophysical survey provides an example of the application of these techniques to evaluate the spatial variability of SWC in two different water conditions. The contribution of geophysical data in understanding the spatial variability of SWC was investigated applying both the traditional analysis and spatial techniques. The results indicated that the geophysical data captured the spatial variation of SWC in non-invasively way especially in dry condition. However, they also showed the complex interplay between factors controlling SWC and geophysical responses and the drawbacks of geophysical sensors under inhomogeneous water conditions. Our findings also highlighted that EMI survey provides the potential to map the SWC variability within a relatively short time. The results obtained in this research are important from the agronomical viewpoint, since they allow increasing efficiency of irrigation practices, which is important in times characterized by climate change.(AU)

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In most Latin American countries there are significant numbers of both missing people and forced disappearances, ∼71,000 Colombia alone. Successful detection of buried human remains by forensic search teams can be difficult in varying terrain and climates. Three clandestine burials were simulated at two different depths commonly encountered in Latin America. In order to gain critical knowledge of optimum geophysical detection techniques, burials were monitored using: ground penetrating radar, magnetic susceptibility, bulk ground conductivity and electrical resistivity up to twenty-two months post-burial. Radar survey results showed good detection of modern 1/2 clothed pig cadavers throughout the survey period on 2D profiles, with the 250MHz antennae judged optimal. Both skeletonised and decapitated and burnt human remains were poorly imaged on 2D profiles with loss in signal continuity observed throughout the survey period. Horizontal radar time slices showed good anomalies observed over targets, but these decreased in amplitude over the post-burial time. These were judged due to detecting disturbed grave soil rather than just the buried targets. Magnetic susceptibility and electrical resistivity were successful at target detection in contrast to bulk ground conductivity surveys which were unsuccessful. Deeper burials were all harder to image than shallower ones. Forensic geophysical surveys should be undertaken at suspected burial sites.

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Unconsolidated pyroclastic flow deposits of the 1993 eruption of Lascar Volcano, Chile, have, with time, become increasingly dissected by a network of deeply penetrating fractures. The fracture network comprises orthogonal sets of decimeter-wide linear voids that form a pseudo-polygonal grid visible on the deposit surface. In this work, we combine shallow surface geophysical imaging tools with remote sensing observations and direct field measurements of the deposit to investigate these fractures and their underlying causal mechanisms. Based on ground penetrating radar images, the fractures are observed to have propagated to depths of up to 10 m. In addition, orbiting radar interferometry shows that deposit subsidence of up to 1 cm/year-1 occurred between 1993 and 1996 with continued subsidence occurring at a slower rate thereafter. In situ measurements show that 1 m below the surface, the 1993 deposits remain 5°C to 15°C hotter, 18 years after emplacement, than adjacent deposits. Based on the observed subsidence as well as estimated cooling rates, the fractures are inferred to be the combined result of deaeration, thermal contraction, and sedimentary compaction in the months to years following deposition. Significant environmental factors, including regional earthquakes in 1995 and 2007, accelerated settling at punctuated moments in time. The spatially variable fracture pattern relates to surface slope and lithofacies variations as well as substrate lithology. Similar fractures have been reported in other ignimbrites but are generally exposed only in cross section and are often attributed to formation by external forces. Here we suggest that such interpretations should be invoked with caution, and deformation including post-emplacement subsidence and fracturing of loosely packed ash-rich deposits in the months to years post-emplacement is a process inherent in the settling of pyroclastic material.

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A Ground Penetratin Radar (GPR) water level monitoring study of a mature transitional tropical forest is presented. Three water tables monitoring wells were installed during 2001/2002 at three different sites: under permanent forest, under managed forest and pasture. The GPR profiles show that the water table appears as a strong horizontal reflector in March and August, 2002,and as a weak, discontinuous reflector during measurements in May and October 2001. Due to several laterite lenses in the soil, the water table can easily be mistaken in place of such lenses. Soil moisture had an influence on these reflection signals, changing the dielectric constant of soil. The depth of the water table varied 1.8 m under permanent forest, 0.9 m under management forest and 3.7 m under pasture.

Um estudo do monitoramento do nível de água foi realizado com medidas diretas e com Radar de Penetração no Solo (GPR) em uma floresta tropical de transição para o cerrado. Três poços de monitoramento do nível de água foram instalados durante 2001/2002 em três locais diferentes: o primeiro em uma área de floresta permanente, outro em área de floresta manejada e outra em uma área de pasto. Os perfis de GPR mostram que o nível do topo do lençol freático aparece como um refletor horizontal forte em março e em agosto de 2002, e como um refletor fraco durante medidas em maio e outubro de 2001 com descontinuidades devido a diversas lentes de solo laterítico no solo. O topo do lençol de água é facilmente confundido com a presença de tais lentes. A umidade do solo teve uma influência nestes sinais da reflexão, mudando a constante dielétrica do solo. A profundidade do topo do lençol da água variou 1,8 m sob a floresta permanente, 0,9 m sob a floresta manejada e 3,7 m sob o pasto.