Publications

  • Ilaria C. Galiano · Gabriele Uras · Roberto Balia

    No preview · Article · Apr 2015 · Rendiconti Online Societa Geologica Italiana
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    R. Balia · A. Viezzoli
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    ABSTRACT: The problem of aquifers and soil salinity is addressed in the coastal area of Muravera (SE Sardinia, Italy) with the combined use of electrical resistivity and induced polarization measurements along three lines, and with 41 Transient Electromagnetic (TEM) soundings distributed in the study area. The resistivity and chargeability sections provide a detailed information on the hydrogeological conditions in the first 20 - 60 m depth, clarifying the role of both clay and salt water and eventually confirming the local near-surface hydrogeological model. The resistivity maps obtained for different depth ranges by TEM data inversion, give a clear and effective representation of the saline contamination both laterally and down to a depth of about 70 m, over the whole investigated area. The combination of the geophysical techniques (resistivity tomography with Induced Polarization measurements, integrated with TEM soundings) proves very effective as an approach for soil and water salination monitoring.
    Full-text · Article · Mar 2015 · Bollettino di Geofisica Teorica ed Applicata
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    Roberto Balia

    Full-text · Chapter · Apr 2012
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    Ghiglieri G · Balia R · Oggiano G · Pittalis D
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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.
    Full-text · Article · Jun 2010 · Hydrology and Earth System Sciences
  • 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.
    No preview · Article · Feb 2010 · Journal of Geophysics and Engineering
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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.
    Full-text · Article · Nov 2009 · Hydrology and Earth System Sciences Discussions
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    R. Balia · F. Ardau · G. Barrocu · E. Gavaudo · G. Ranieri
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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 300 m, 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 350-400 m is very low. The condition of seawater intrusion affecting the aquifers is also elucidated.
    Full-text · Article · Jun 2008 · Hydrogeology Journal
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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.
    Full-text · Article · Jan 2008
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    F. Ardau · R. Balia · M. Bianco · J. De Waele
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    ABSTRACT: The SW part of Sardinia has been afflicted, in recent years, by several cover-collapse sinkholes mostly occurring in low-density population areas. The study area, that lies in the Iglesiente-Sulcis region, is characterized by the cropping out of the Palaeozoic basement related to the South European Hercynian chain, covered with Tertiary-Quaternary sediments. The main rock types that crop out are Palaeozoic metasandstones, metadolostones, metalimestones, shales and metaconglomerates, and Tertiary-Quaternary fluvial-lacustrine continental sediments. The combined application of several geophysical techniques, integrated with boreholes and geotechnical as well as hydrogeological measurements, proved to be very useful and promising in defining in detail the geological context in which each sinkhole has formed. Moreover, the gravity method, even when used alone, proved to be very effective in detecting the regional geological structures to which sinkholes are related. Eventually, the historical analysis of phenomena, the geological knowledge of the Iglesiente-Sulcis area and the results of properly designed geophysical surveys allows the most probable areas for cover-collapse sinkholes to occur in the future to be determined. In fact, this research pointed out that the depth of the sediment-covered Palaeozoic bedrock is one of the major constraints in delimiting hazardous areas, leading to the construction of a preliminary hazard map. This map shows a belt of high risk, and also suggests the ares in which further geophysical and geotechnical investigations should be carried out to estimate the depth of the bedrock.
    Full-text · Article · Jan 2007 · Geological Society London Special Publications
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    Full-text · Chapter · Jan 2006
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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
    Full-text · Article · Sep 2003 · Geophysics
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    Roberto Balia
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    ABSTRACT: Geophysical surveys have been carried out aimed at guiding axcavations, specifically for finding tombs of Proto-Axumite and Early Axumite period. The geophysical results allowed to compile a "priority map" to guide archeological excavations. During the next excavation campaign two tombs corresponding to geophysical anomalies were unearthed.
    Full-text · Article · Jan 2003
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    Balia

    Full-text · Article · Jan 2003
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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
    Full-text · Article · Aug 2001
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    G. P. Deidda · R. Balia
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    ABSTRACT: An SH-wave seismic reflection experiment was conducted to evaluate the feasibility and cost effectiveness of reflection imaging ultrashallow targets commonly encountered in engineering, groundwater, and environmental investigations. It was carried out on a purpose-built subsurface ground model consisting of a concrete layer, at a depth from 2.85-5 in, and a low-velocity overburden (< 80 and 150 m/s for S- and P-waves., respectively), constituted of filling material. with the water table 2.60 in deep. High-quality CDP data, acquired by using a 10-kg sledgehammer and newly designed horizontal detectors, allowed us to obtain an extremely detailed stacked section with a minimal amount of processing. Uncertainty in determining the depth and horizontal dimensions of the concrete model was estimated to be 0.2 and 0.3 in, respectively; however, the dominant frequencies lower than 150 Hz, the low-transmission coefficient at the upper interface, and the relatively high velocity (900 m/s) of the concrete layer prevented us from resolving the layer thickness. The experiment demonstrates that when overburden materials exhibit low velocities (a common condition in near surface), the SH-wave seismic reflection method is a reliable, detailed, and cost-effective technique to image ultrashallow targets, even in disturbed material and below the water table.
    Full-text · Article · Jul 2001 · Geophysics
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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.
    Full-text · Article · Sep 2000 · Journal of Applied Geophysics

  • No preview · Conference Paper · Jan 2000
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    ABSTRACT: In this paper an example is given of an application of statistical techniques to the Bouguer anomalies analysis in order to design a simple crustal model using few a priori assumptions. All gravity measurements carried out in Sardinia have been collected and processed. The Bouguer anomalies have been calculated according to local density estimates. Spectral analysis of the Bouguer anomalies has been carried out along selected profiles in order to estimate the mean depth of the Moho discontinuity and that of an infracrustal discontinuity. The use of this technique inferred the presence of a discontinuity at a mean depth of ~ 28 km, interpreted as Moho and the likely presence of an infracrustal discontinuity at a mean depth of ~18 km, interpreted as the upper-lower crust transition. In order to roughly reconstruct the shape of these interfaces, 2D inversion techniques were applied to the large wavelength components of the Bouguer anomalies, relative to profiles oriented along the E-W direction, extracted from low-pass filtered Bouguer anomaly maps. The density model obtained is compatible with some velocity models achieved from the interpretation of the seismic refraction profiles carried out within the European Geotraverse project.
    Full-text · Article · Jan 1997
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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.
    Full-text · Article · Jan 1994 · Annals of geophysics = Annali di geofisica
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    Full-text · Article · Jan 1994

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