Publications

  • R Balia, B Littarru
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    ABSTRACT: Two examples of combined application of geophysical techniques for the pre-reclamation study of old waste landfills in Sardinia, Italy, are illustrated. The first one concerned a mine tailings basin and the second one a municipal solid waste landfill; both disposal sites date back to the 1970–80s. The gravity, shallow reflection, resistivity and induced polarization methods were employed in different combinations at the two sites, and in both cases useful information on the landfill's geometry has been obtained. The gravity method proved effective for locating the boundaries of the landfill and the shallow reflection seismic technique proved effective for the precise imaging of the landfill's bottom; conversely the electrical techniques, though widely employed for studying waste landfills, provided mainly qualitative and debatable results. The overall effectiveness of the surveys has been highly improved through the combined use of different techniques, whose individual responses, being strongly dependent on their specific basic physical characteristic and the complexity of the situation to be studied, did not show the same effectiveness at the two places.
    Journal of Geophysics and Engineering 02/2010; 7(1):64. · 0.72 Impact Factor
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    ABSTRACT: A multidisciplinary research effort, including geological, hydrogeological, hydro-chemical, geophysical and hydrological investigations, was aimed at locating a source of safe groundwater for a district of northern Tanzania, within the western branch of the East Africa Rift Valley, where water shortage is common and much of the surface water carries unacceptable levels of dissolved fluoride. The 440 km2 study area lies in the northern part of Arumeru district and is dominated by Mt. Meru (4565 m a.s.l.). The local climate is semi-arid, with distinct wet and dry seasons. Four hydrogeological complexes were identified, occurring within different volcanic formations, either alone or superimposed upon one another. The groundwater flow system was interpreted from the spatial distribution of the springs, combined with a lithology- and geometry-based reconstruction of the aquifers. The dominant pattern consists of a multi-directional flow from the higher elevations in the south towards the lower areas in the north, but this is complicated by structures such as grabens, faults, lava domes and tholoids. After the identification of the major fluoride source, an interference pattern between groundwater and high fluoride surface water was drawn. Finally, vertical electrical soundings were performed to define the location of aquifers in regions where release of fluoride was prevented. The methodological approach for the prospecting of safe water in a semi-arid, fluoride polluted region was validated by the drilling of a 60 m deep well capable of supplying at least 3.8 l/s of low fluoride, drinkable water.
    Hydrology and Earth System Sciences 01/2010; · 3.59 Impact Factor
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    ABSTRACT: This research was aimed at finding fresh and safe groundwater easily deliverable to an area, located in northern Tanzania, within the western branch of the Rift Valley. The study area suffers from water shortage, moreover, due to widespread alkaline volcanism, high fluoride contents (F<sup>-</sup> up to 70 mg/l) affects the groundwater. The achievement of this goal has been pursued through a multidisciplinary research consisting of geological, hydrogeological, hydro-chemical, geophysical and hydrological investigations. The study area stretches over 440 km<sup>2</sup> and lies in the northern part of the Arumeru District, approximately 50 km from Arusha, the capital of the region. The Mount Meru (4565 m a.s.l.) and the Arusha National Park mark the boundary of the area, which includes 9 villages belonging to the Oldonyo Sambu and Ngarenanyuki Wards. The climate is semi-arid, with dry and relatively rainy seasonal alternance. Four principal hydrogeological complexes have been identified within different lithologies. They occur within volcanic formations, singularly or superimposed on each other. Subordinate perched aquifers are present in sedimentary formations with local occurrence. The groundwater flow system has been interpreted on the basis of springs spatial distribution combined with lithological and the geometrical reconstruction of the aquifers. The dominant pattern, consisting of multidirectional flow from the higher elevation area in the south towards the lower area in the north, is complicated by the occurrence of structures such as grabens, faults, lava domes and tholoids. After the identification of the main fluoride source, an interference pattern among groundwater and high F surface water was drawn. Finally, some VES (Vertical Electrical Sounding) were performed that allowed an aquifer to be individuated within a structural high where the fluoride input is prevented. The drilling of a well, able to supply at least 3.8 l/s of low fluoride, drinkable water, successfully concluded the methodological approach for prospecting safe water in a semi-arid, naturally fluoride polluted region.
    01/2009;
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    ABSTRACT: Due to water shortage, in the wards of Ngarenanyuki and Oldonyosambu (Arumeru District, Northern Tanzania), the per capita daily water consumption is 8 liters as.average, The avaleability goes down to 3-4 liters in the dry seasons when most of the population cannot resort to seasonal ponds or streams and so it is compelled to concentrate around the few perennial water points. This datum is quite far from the Millennium Goal objectives that foresee a quantity of at least 20 l/d/p (litres per day per person) for the Development Countries population, within 2015. Problems are also related to water quality, in particular, the high concentration of fluoride that characterises the waters in East Africa Rift System.
    01/2008;
  • Geological Society, London, Special Publications. 01/2007; 279(1):47-57.
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    01/2006: pages 47-57;
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    ABSTRACT: In the study of coastal plains affected by soil and water salination, a knowledge of several geological aspects, such as structural features, depth to basement, stratigraphy of sedimentary cover, relationships between the phreatic aquifer and underlying aquifers, and the latter's structure, is basic to gaining an adequate understanding of both the causes and possible evolution of salination. In this framework, geophysical techniques can play a very important role.To improve the available geophysical information about the Muravera coastal plain, Sardinia, Italy, which is affected by severe soil and water salination, previously acquired electrical resistivity, reflection seismic and gravity data have been reprocessed, and a new seismic reflection survey has been conducted. Moreover, in order to give better support to the geological and hydrogeological interpretation of geophysical data, three boreholes were drilled. Reprocessed electrical data indicate the presence of a wide, electrically homogeneous low-resistivity zone associated with salination phenomena. Reprocessed reflection data provide useful information on the near-surface stratigraphy. The combined interpretation of resistivity and seismic results, supported by one calibration borehole, elucidates the relationships between the phreatic aquifer and the underlying confined aquifer. A new seismic reflection survey gives information on the depth to, and structure of, the Paleozoic basement, as well as on stratigraphic conditions of Pleistocene-Holocene sediments. Finally, the combined interpretation of seismic, gravity, and well data results in a geological section containing most of the information considered essential, such as the interface between Holocene alluvium and Pleistocene alluvium, the thickness of the latter, and the structure and composition of the Paleozoic basement.The work as a whole shows how the combined application of geophysical techniques can in this specific situation provide wide-ranging and high-quality information that is essential for the realistic mathematical modeling of aquifer contamination, and can enable the rational planning of exploratory drillings
    01/2003;
  • G. P. Deidda, R. Balia
    Geophysics 01/2001; 66(4). · 1.72 Impact Factor
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    ABSTRACT: High-resolution shallow seismic reflection surveys require more attention to the choice of source and configuration, receivers and recording geometry for optimizing data acquisition than conventional oil exploration surveys. Moreover, some standard processing techniques to increase signal/noise (S/N) ratio need special accuracy (for example, surgically precise removal of early-time coherent noise and iterative, small time shift static corrections). This paper compares results obtained using different sources at two test sites: explosive, cap, shotgun, hammer and weight drop. Data from experiments using geophones with different natural frequencies and using various acquisition geometries are also compared. In data processing, it is demonstrated how increasing the S/N ratio for high-resolution results requires special consideration in some common processing steps (F–K filter, first arrivals muting, elimination of air wave and static corrections). The comparison, based on shot gathers and stack sections, shows that attenuation of high frequencies by the earth is the most significant influence on the spectral properties of the data, as expected the source itself also does have some influence on frequency content, depending to some extent on surface conditions. The high-velocity explosive sources produced the highest frequency reflections and best S/N ratio, because they have higher energy related to higher burn/blast velocity and source containment then the other sources and they are used in hole (i.e. below ground surface where the air wave energy is more attenuated) but the shotgun also an explosive source was reasonably comparable to high explosive when used in hole. Special care must be taken during processing to insure artifacts are distinguished from real reflection events.
    Journal of Applied Geophysics 01/2000; · 1.33 Impact Factor
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    ABSTRACT: A Spectral Induced Polarization (SIP) survey was carried out in a mining test site in Sardinia (Italy). Measurements were developed along a profile by using an axial dipole-dipole array with 10 AB positions and 6 MN positions for cach AB. The amplitude and phase spectra of the apparent resistivity were acquired in the 0.25-4096 Hz frequeney range. The results obtained through the processing and inversion step seem to confirm that, with respect to the classical TD/FD Induced Polarization, SIP allows better discrimination of some important characteristics of mineral deposits such as mineral content and grain size.
    Annals of geophysics = Annali di geofisica 01/1994; 37(Suppl. 5):1313-1321. · 1.14 Impact Factor
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    Geologica Romana. 01/1994; 30:239-244.
  • R. Balia
    Tectonophysics 09/1991; 195(2-4):347-358. · 2.68 Impact Factor
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    ABSTRACT: The present study reports on a telluric profile, carried out over the Campidano graben, which is one of the most interesting structures in Sardinia. The telluric data, which were interpreted together with magnetotelluric, gravity, electrical and magnetic data, depict the form of the graben with a remarkable degree of mutual consistency and reliability. The results confirm the value of a combined interpretation in solving complex problems, where the application of a single method may give only an ambiguous or incomplete solution.
    Geoexploration 01/1991; 28(1):43-54.
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    ABSTRACT: In order to achieve a better definition of the geothermal potential in the area of the Campidano graben (Sardinia, Italy), where there are some thermal springs, a multi-methodological geophysical survey has been combined with recent surface and subsurface geological information. New gravity and magnetic stations, distributed over the northern part of the area (Campidano of Oristano), have been measured to complement already published data for the central-southern part of the graben. Deep dipole geoelectrical soundings have also been performed along two profiles perpendicular to the strike of the graben. The geological interpretation of the geophysical data allows us to conclude that no shallow, exploitable geothermal reservoir exists in the survey area.
    Geothermics. 01/1991;
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    ABSTRACT: Aeromagnetic data are interpreted to better understand the relationship between the southern part of the Oligo-Miocene rift and the Plio-Quaternary Campidano Graben on Sardinia. Particular reference is made to the geostructural location of the Campidano Graben. The aeromagnetic data have been interpreted by applying three different methods to the original survey data: spectral analysis, analytical signal and Werner deconvolution. The results of this study give first-order estimates of the depth of the magnetic basement and position of major dykes in the study area and on the efficiency of the inversion methods used.
    Tectonophysics. 01/1991;
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    ABSTRACT: A study of geomagnetic field time variations with a magnetometric array was performed in Sardinia during the summer of 1988. Nine fluxgate magnetometers with digital acquisition systems were employed to cover the main structural features of the island. The recordings do not show significant variations in the amplitudes of the horizontal components of the bay-like events, whereas the vertical component amplitudes show a strong southward increase. Fourier maps were drawn at significant periods, and induction arrows and DeltaZ/DeltaH pseudosections were derived.
    Physics of The Earth and Planetary Interiors 01/1991; 66(1):92-100. · 2.38 Impact Factor
  • Annales Geophysicae 01/1985; 3(3):365-368. · 1.52 Impact Factor
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    ABSTRACT: A gravity survey of the Campidano geothermal fields and surrounding region was conducted in 1981. It covered an area of 1900 km2 and included 952 uniformly distributed stations. The Bouguer anomaly is generally negative within the Campidano graben, reaching −10 mgal in the central zone, whereas a positive Bouguer anomaly prevails outside the graben, exceeding 20 mgal in several areas. The gravity data were interpreted using spectral analysis and two-dimensional models, to determine the thickness of sediments and andesitic volcanics within the graben. The total thickness of these formations reaches 3000 m in the centre, but is reduced elsewhere, especially towards the sides of the graben. The thermal springs on both the eastern and western sides of the graben are associated with residual positive anomalies and are near very steep gradients in the Bouguer anomaly.
    Geothermics 01/1984; 13(4):333-347. · 2.86 Impact Factor
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    ABSTRACT: Hydrogeological and geophysical surveys confirm that the aquifers of the Capoterra plain in Sardinia (Italy) constitute a complex, multilayer system. In the north-east of the plain, this system is composed of a shallow aquifer of recent alluvium and a deeper aquifer separated from the former by a clay layer; in the south-west there is no separation between the two aquifers. The deepest and most important member of the multilayer aquifer system is situated at the transition from Quaternary to Miocene sediments. With respect to deep structures and stratigraphy, several differentiations inside the Miocene sedimentary filling, whose overall thickness is in the order of 300m, have been found. The combined interpretation of several datasets allows the Capoterra plain to be reliably modelled from surface to a depth of several hundreds of metres and provides the possibility of finding deeper groundwater resources. Concerning the latter, since Miocene materials are known to be impermeable in the middle of the plain, in contrast to the aquifers hosted in the Quaternary sediments and alluvium, the probability of finding fresh water at a depth of less than 350–400m is very low. The condition of seawater intrusion affecting the aquifers is also elucidated. Les études hydrogéologiques et géophysiques confirment que les aquifères de Capoterra, plaine de Sardaigne (Italie), constituent un système complexe et multicouches. Au nord-est de la plaine, ce système est constitué d’un aquifère superficiel d’alluvions récentes séparé d’un aquifère profond par des argiles. Il existe une continuité entre ces deux aquifères dans sa partie sud-ouest. La partie profonde de l’aquifère composée de dépôts sédimentaires du Quaternaire et Miocène est la plus importante du système multicouche. Plusieurs différences dans la stratigraphie et les structures profondes peuvent être mises en évidence au sein du remplissage Miocène qui est d’épaisseur globale de l’ordre de 300m. L’interprétation de l’ensemble des données permet la modélisation de la plaine de Capoterra depuis la surface jusqu’à plusieurs centaines de mètres de profondeur ce qui donne la possibilité de trouver des ressources en eaux à grande profondeur. Toutefois, du fait que le matériel composant le Miocène est connu comme étant imperméable au centre de la plaine au contraire de l’aquifère quaternaire et alluvions, la probabilité de trouver de l’eau douce à des profondeurs de moins de 350–400m est faible. La dynamique de l’intrusion marine affectant l’aquifère est également comprise. Los relevamientos hidrogeológicos y geofísicos confirman que los acuíferos de la planicie de Capoterra en Cerdeña (Italia) constituyen un sistema multicapa complejo. En el noreste de la llanura, este sistema está compuesto por un acuífero somero aluvial reciente y un acuífero profundo separado del anterior por una capa arcilla; en el sudoeste no existe separación entre los dos acuíferos. El miembro más importante y más profundo del sistema acuífero multicapa está situado en la transición de los sedimentos Cuaternarios a los Miocenos. Con respecto a las estructuras profundas y a la estratigrafía, se han encontrado varias diferenciaciones dentro del relleno sedimentario Mioceno, cuyo espesor total es del orden de 300metros. La interpretación combinada de varios conjuntos de datos permite modelar en forma confiable a la llanura de Capoterra desde la superficie hasta una profundidad de varios cientos de metros y ofrece la posibilidad de localizar recursos de agua subterránea a mayor profundidad. En relación con estos últimos, puesto que se conoce que los materiales del Mioceno son impermeables en la parte media de la llanura, en contraste con los acuíferos reconocidos en los sedimentos Cuaternarios y aluviales, la probabilidad de encontrar agua dulce a profundidades menores de 350–400m es muy baja. Se analizó también la posibilidad de afectación de la intrusión marina en los acuíferos. Levantamentos hidrogeológicos e geofísicos confirmam que os aquíferos da planície de Capoterra na Sardenha (Itália) constituem um sistema complexo e multicamada. No nordeste da planície, este sistema é composto por um aquífero superficial aluvionar de idade recente e um aquífero mais profundo, separado do primeiro por uma camada de argila; a sudoeste esta separação entre os dois aquíferos não existe. A mais profunda e principal zona do sistema aquífero multicamada situa-se na transição dos sedimentos Quaternários para Miocénicos. No que diz respeito a estratigrafia e estruturas profundas, foram encontradas várias diferenciações no preenchimento sedimentar Miocénico, cuja espessura total é da ordem de 300m. A interpretação articulada de vários conjuntos de dados permite a modelação fiável da planície de Capoterra, desde a superfície até uma profundidade de várias centenas de metros, e fornece a possibilidade de encontrar águas subterrâneas mais profundas. Relativamente a esta última questão, uma vez que os sedimentos Miocénicos são conhecidos por serem impermeáveis no centro da planície, em contraste com os aquíferos instalados nos sedimentos Quaternários e no aluvião, a probabilidade de encontrar água doce a uma profundidade inferior a 350–400m é muito reduzida. Também é esclarecida a intrusão marinha que afecta os aquíferos.
    Hydrogeology Journal 17(4):981-997. · 1.68 Impact Factor
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    ABSTRACT: The Middle Tirso Valley is located in Central Sardinia and lies between two structural highs, the Marghine-Goceano chain and the Barbagia Paleozoic horst. The geological structures of the area, potentially interesting for its geothermal resources, are rather complex and dominated by two regional faults – the Marghine fault and the Nuoro fault – which affect the Palaeozoic basement and the Tertiary volcano-sedimentary deposits. Combined modelling of gravity and geoelectrical data defines the shape and extent of this Tertiary basin. The Bouguer anomaly is mainly characterized by a three-dimensional gravity low which has been named «Bolotana-Sedilo gravity low», corresponding to a structure generated by collapses attributable to transcurrent and extensional tectonic events. The down faulted zone is filled with a Tertiary low density volcano-sedimentary sequence extending southwards and overlain by Pliocene-Quaternary basalts. Another regional structure named «Tirso Fault» is proposed

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