High-resolution Geophysical Surveys Research Articles

Geophysical Study of the Diendorf-Boskovice Fault System (Austria)

We describe here the results of the characterization of subsurface structures in an area of the south-eastern edge of the Bohemian Massif, in Austria by high-resolution geophysical survey techniques and advanced analysis methods of potential fields. The employed methods included potential field multiscale techniques for source-edge location and characterization of sources at depth. Our results confirmed the presence of already known structures: the location of the Diendorf Fault and the Moldanubian Shearzone are clearly recognized in the data at the same location as on the geological maps, even where the Diendorf fault is covered with sediments of the Molasse Basin. In addition, we detected several geological contacts between different rock types in the Bohemian Massif west of the Diendorf Fault. From our results, we were also able to quickly identify and image, without a priori information, previously unknown structures, such as faults with-depth-to-the top of about 500 m and magmatic intrusions about 400 m deep.

Thermal Spring System Plumbing across a Major Normal Fault: Pah Tempe, Utah, USA

Abstract Faults, including their cores and associated fracture zones, can play an important role in controlling the flow of ground water. Pah Tempe Hot Springs at Timpoweap Canyon in southwestern Utah provides excellent exposures of the damage zone of a major normal fault and associated groundwater discharge. This includes numerous point discharges of ~40°C Na-Cl water into the Virgin River along a ~500 m stretch of the footwall damage zone of the Hurricane fault, part of the greater Wasatch-Hurricane fault system. An impermeable fault core and fine-grained rocks in the hanging wall impede cross-fault flow and force thermal waters to rise to the surface. The spectacular canyon-wall exposures permit an investigation of a fractured bedrock vadose zone as an analogue to subjacent aquifers. Photogrammetry (visual and infrared) enabled the mapping of discrete inflow locations, as well as permeable discontinuities in the canyon walls. Geochemistry, including reaction-path models, defined plausible chemical evolution pathways of thermal waters, whereas high-resolution geophysical surveys provided information on subsurface disruption and the depth to bedrock beneath Virgin River channel alluvium. The synthesis of these approaches indicates that permeable pathways in fractured carbonate rocks exhibit heterogeneous patterns. Some rock volumes contain abundant permeable fractures, bedding-plane partings, and solution cavities. Yet, within such volumes, one fracture may be permeable, whereas another only a few cm away may not. On a large scale (tens of meters), entire volumes of bedrock may be impermeable. Geophysical studies can shed light on gross fracture patterns in the bedrock aquifer but are incapable of showing which features accommodate flow. Patterns of permeability in the thick vadose zone may be the best predictor of subjacent flow paths in the aquifer. Thermal waters represent the leakage of deep brines or the mixing of Virgin River underflow with deep brines. Carbonate rocks exhibit self-organization where stochastic distribution of fracture apertures channel flow into wider features that channel additional flow. In turn, these features self-widen through solution weathering. By contrast, siliciclastic and basement rocks are not nearly as prone to dissolution. Thus, fluxes are partitioned into north-south fractures that will tend to have aperture in this east-west extending region. The results of this study help improve the conceptualization of flow systems near fault zones, and the methods employed may be a template applicable to the study of other systems.

The sanctuary of Apollo in Pompeii: new geophysical and archaeological investigations

The paper discusses recent and integrated investigations in the Sanctuary of Apollo in Pompeii, which contribute to the overall understanding of the diachronic evolution of this sacred place, from the archaic period to the eruption of AD 79. High-resolution geophysical surveys have been interpreted in comparison with a new reading of the publication of Maiuri’s excavations and the most recent excavations. The latest research offers significant additional information, not only on the constructive episodes of the architectural complex and the urban landscape in which it is inserted, but also on aspects related to the cult of Apollo and the associated rituality.

Characterization of the shallow structure of El Tatio geothermal field in the Central Andes, Chile using transient electromagnetics

This study presents the first high resolution geophysical survey conducted in The El Tatio geothermal field, northern of Chile, focused on the detection of shallow subsurface structures and identification of ascending fluid pathways. TEM data was collected along 5 profiles crossing the two main geothermal basins (Upper and Middle Basin) to obtain an electrical resistivity model up to 200 m depth. The models show important structures that allowed us to improve the conceptual model of the field connecting these geophysical observations with the geology and the geochemistry of the area. We found a shallow (<60 m) high conductivity layer in all profiles. This layer was interpreted as a shallow aquifer of thermal water, which is probably the water supplier of surface manifestations. In the Upper Basin a main permeable zone allows the ascent of fluids from deep aquifers to the shallower one, and a structure that probably act as impermeable geological barrier that forces the fluids to ascend has been detected. In the Middle Basin fluid ascent zones are less clear than in the Upper Basin but it is possible to observe areas of lower resistivity that could be associated with higher permeability.

A „Kapos-vonal” középső szakaszának szerkezeti-mélyföldtani viszonyai és neotektonikai jellegei a legújabb geofizikai vizsgálatok tükrében

Tanulmányunkban a Kapos-vonal középső szakaszának legújabb geofizikai vizsgálatainak eredményeit tekintjük át. Munkánkkal tavaly ősszel elhunyt Kollégánk, Barátunk, Tanárunk és Mesterünk — Prof. Dr. Horváth Ferenc — emléke előtt tisztelgünk. A kutatási területen elérhető korábbi és újonnan mért 2D/3D reflexiós szeizmikus és fúrási adatok integrációjával komplex adatbázist alakítottunk ki, amelynek értelmezésével földtanilag és geometriailag egyaránt konzisztens, új 3D földtani-tektonikai modellt hoztunk létre. A modell a vizsgált terület földtani felépítésének alapvonásait szem előtt tartva öt meghatározó jelentőségű földtani horizont (prekainozoos aljzat-tető, alsó-miocén tető, középső-miocén tető, Endrődtető, Algyő-tető) és az értelmezett vetők téradatrendszerét tartalmazza. A kialakított 3D modell alapján elvégeztük a korábbi vizsgálatokkal nyert földtani-szerkezeti kép felülvizsgálatát, és azt szükség szerint módosítottuk, illetve pontosítottuk/kiegészítettük.A kutatás mélyföldtani szempontból legfontosabb eredményei közé tartozik a kristályos és mezozoos aljzat képződmények szerkezeti, elterjedési és kifejlődési viszonyainak reambulációja a lemélyült új szerkezetkutató fúrások és a szeizmikus adatrendszer integrált értelmezése alapján. Ugyancsak alapvető jelentőségű a markáns kora-miocén riftesedés kimutatása, amely során intenzív, többfázisú mészalkáli vulkáni működés, illetve egyidejű kontinen tális üledékképződés zajlott a létrejött, helyenként akár 2 km mélységű süllyedékekben. Mindez tágabb kontextusban a Pannon-medence korábban kevésbé ismert (és hangsúlyozott) kora-miocén kialakulási szakaszának jelentőségére hívja fel a figyelmet. A vetőtérképezés eredményei alapján a szűkebb kutatási terület meghatározó vetőzónái a KÉK–NyDNy-i csapású „Kapos-vonal”, továbbá az ÉK–DNy-i csapású Dunaszentgyörgy–Harta és az ezen kutatás során először térképezett Bonyhádi vetőzóna, amelyeket mind meredek dőlés (≥60–70°) jellemez. A Bonyhádi vetőzóna délnyugati irányban a Mecsek északi pikkelyzónájához csatlakozik. A terület szerkezeti képét összességében a fentiekkel többnyire (közel) párhuzamos törések uralják, míg az előbbiekre kb. merőleges ÉÉNy–DDK-i csapású, szerkezetileg kevésbé jelentős törések főként a Kapos-vonaltól délre jelentkeznek.Eredményeink alapján geometriai-szerkezeti értelemben egységes Kapos-vonal nem létezik: e vetőzóna a kutatási területen ugyanis egy nyugati („Kapos-Ny”) és egy keleti szegmensre („Kapos-K”) bontható, amelyek mind dőlés irányban, mind az észlelt neotektonikus aktivitásban — összhangban a korábbi szakirodalmi adatokkal — markánsan különböznek. A vizsgált területen élénk neotektonikus aktivitást mutató Kapos-K, Dunaszentgyörgy–Harta és Bonyhádi vetőrendszerek regionális léptékben egy ÉK–DNy-i és KÉK–NyDNy-i csapású elemekből felépülő, széles nyírási zónát körvonalaznak, amely a neotektonikus fázisban balos eltolódásként működött. Ezt igazolja az egyes vetőzónákban megfigyelt tipikus „virágszerkezetet” mutató belső struktúra, továbbá a kapcsolódó másodlagos formaelemek (Riedel-törések) is.A kialakított 3D modell eredményeinek figyelembevételével telepített nagyfelbontású 2D és pszeudo-3D sekélygeofizikai vizsgálatok, valamint az ezek eredményei alapján kijelölt árkolás és sekélyfúrások adatai bizonyították a Dunaszentgyörgy–Harta vetőzóna negyedidőszaki, sőt az árkolás eredményei szerint késő-negyedidőszaki aktivitását, hiszen a kutatóárokban feltárt késő-pleisztocén végi futóhomok tektonikus eredetű deformációja jelentkezett. A fiatalnegyedidőszaki tektonikai aktivitást a kutatási területen számos további korábbi, illetve a jelen kutatáshoz kapcsolódó, de e tanulmányban nem részletezett neotektonikai megfigyelés is alátámasztja. Mindezen eredmények a szak irodalomban a Kapos-vonal keleti szakaszáról (Duna–Tisza köze és Tiszántúl) közölt tektonikai adatokkal és értelmezésselteljes összhangban állnak.A tanulmányunkban ismertetett eredmények a Paks II földtani kutatási programjának (FKP) keretében 2015–2016 során elvégzett földtani-geofizikai kutatásokhoz kapcsolódnak.

Quantitative appraisal of Heliborne and ground-based Time Domain Electromagnetic surveys for uranium exploration – A case study from Rajasthan, India

Soda-metasomatised and metasediments hosted uranium deposits constitute 18% of the world?s uranium resources. In India, such deposits are identified along the albitite line in the environs of North Delhi Fold Belts in the state of Rajasthan. These are structurally controlled with association of albitisation and pyroxenisation of metasediments, metallic sulphides and carbonaceous phyllites. Uraninite is the dominant mineral phase along with copper, molybdenum and sulphides. The low resistivity of the fractures associated with metallic minerals produces a significant contrast with the host rock, which can be located with electromagnetic methods. High-resolution heliborne geophysical surveys comprising of VTEM, magnetic and gamma-ray spectrometric were conducted to identify uranium deposits in the vicinity of albitite zone. This paper demonstrates the results of heliborne and ground followup geophysical surveys to prioritize targets for uranium exploration. For the first time in India, a ground based Time Domain Electromagnetic survey employing Geonics EM37 system was conducted over one of the target areas delineated based on the VTEM surveys. Interpreted results from ground data correlate well with the spatial locations of the EM conductors delineated from heliborne surveys. Additionally modelling of heliborne and ground data produces comparable physical parameters. The results obtained are extremely useful in planning the boreholes in ongoing exploration programme.

Measurement of Sounds Emitted by Certain High-Resolution Geophysical Survey Systems

Scientific questions regarding the impact of anthropomorphic noise in the marine environment have resulted in an increasing number of regulatory requirements and precautionary mitigation strategies to reduce the risks associated with high-resolution marine geophysical surveys performed in waters subjected to government jurisdiction. An example of regulatory frameworks includes the Marine Mammal Protection Act in the United States and the Marine Strategy Framework Directive 2008/56/EC in the European Union. Regulatory compliance often requires an assessment of the potential ecological risks before initiating a marine geophysical survey. However, the acoustic source data needed to estimate the risk associated with the operation of a given high-resolution survey system are frequently lacking. A comprehensive measurement program was performed to quantify the characteristics of sounds radiated by a variety of commercial marine geophysical survey systems, including boomers, sparkers, airguns, chirp sub-bottom profilers, sidescan sonars, and swath-bathymetric sonars [Crocker and Fratantonio, “Characteristics of high-frequency sounds emitted during high-resolution marine geophysical surveys,” Naval Undersea Warfare Center, Newport, RI, USA, NUWC-NPT Tech. Rep. 12, 203, 2016]. Calibrated acoustic source data, including source levels, source spectra, and beam patterns, were acquired for a total of 18 different marine geophysical survey systems. The data support modeling to estimate the potential ecological impacts resulting from the operation of certain high-resolution marine geophysical survey systems.

Paleochannel and beach-bar palimpsest topography as initial substrate for coralligenous buildups offshore Venice, Italy

We provide a model for the genesis of Holocene coralligenous buildups occurring in the northwestern Adriatic Sea offshore Venice at 17–24 m depth. High-resolution geophysical surveys and underwater SCUBA diving reconnaissance revealed meandering shaped morphologies underneath bio-concretionned rocky buildups. These morphologies are inferred to have been inherited from Pleistocene fluvial systems reactivated as tidal channels during the post- Last Glacial Maximum transgression, when the study area was a lagoon protected by a sandy barrier. The lithification of the sandy fossil channel-levee systems is estimated to have occurred at ca. 7 cal. ka BP, likely due to the interaction between marine and less saline fluids related to onshore freshwater discharge at sea through a sealed water-table. The carbonate-cemented sandy layers served as nucleus for subsequent coralligenous buildups growth.

Exploring Holocene palaeogeography in the ‘white ribbon’: a Mesolithic case study from the Northumberland coast

ABSTRACTMesolithic settlement sites preserved on the north‐east coast of England and in south‐east Scotland drive questions about the relationship between early human settlement and the Holocene palaeogeography of ‘Doggerland’. Palaeogeographical reconstructions before 8000 years ago have been restricted by a lack of sea‐level index points and particularly by sparse nearshore geophysical and geological datasets required for such reconstructions. This paper presents new high‐resolution geophysical survey data from Northumberland's nearshore ‘white ribbon’ which provide a foundation for more accurate palaeogeographical reconstructions within which early prehistoric settlement sites can be more readily understood. High‐resolution bathymetry data collected in the nearshore adjacent to the Mesolithic house site at Howick are integrated with coastal LiDAR, seismic, geological and archaeological datasets to underpin palaeogeographical reconstructions. The reconstructions illustrate changing coastal landscapes during Early Holocene sea‐level rise. The data and interpretations provide a ‘source‐to‐sea’ context for understanding the archaeology at important sites such as Howick and Low Hauxley. Furthermore, they provide a basis for enhancing management of at‐risk coastal prehistoric archaeology and a framework to prospect for and protect further vulnerable nearshore archaeological heritage.

Subsurface structure of a maar–diatreme and associated tuff ring from a high-resolution geophysical survey, Rattlesnake Crater, Arizona

Geophysical survey techniques including gravity, magnetics, and ground penetrating radar were utilized to study the diatreme and tuff ring at Rattlesnake Crater, a maar in the San Francisco Volcanic Field of northern Arizona. Significant magnetic anomalies (+1600nT) and a positive gravity anomaly (+1.4mGal) are associated with the maar. Joint modeling of magnetic and gravity data indicate that the diatreme that underlies Rattlesnake Crater has volume of 0.8–1km3, and extends to at least 800m depth. The modeled diatreme comprises at least two zones of variable density and magnetization, including a low density, highly magnetized unit near the center of the diatreme, interpreted to be a pyroclastic unit emplaced at sufficiently high temperature and containing sufficient juvenile fraction to acquire thermal remanent magnetization. Magnetic anomalies and ground penetrating radar (GPR) imaging demonstrate that the bedded pyroclastic deposits of the tuff ring also carry high magnetization, likely produced by energetic emplacement of hot pyroclastic density currents. GPR profiles on the tuff ring reveal long (~100m) wavelength undulations in bedding planes. Elsewhere, comparable bedforms have been interpreted as base surge deposits inflated by air entrainment from eruption column collapse. Interpretation of these geophysical data suggests that Rattlesnake Crater produced highly energetic phreatomagmatic activity that gave way to less explosive activity as the eruption progressed. The positive gravity anomaly associated with the maar crater is interpreted to be caused by coherent bodies within the diatreme and possibly lava ponding on the crater floor. These dense magnetized bodies have excess mass of 2–4×1010kg, and occupy approximately 5% of the diatreme by volume. Magnetic anomalies on the crater floor are elongate NW–SE, suggesting that the eruption may have been triggered by the interaction of ascending magma with water in fractures of this orientation. GPR imaging of the tuff ring also suggests that substantial land-slip may have occurred on the western rim, perhaps causing part of the tuff ring to collapse into the crater. Strong radar reflections indicative of well-developed weathering horizons are present as well. The techniques employed at Rattlesnake Crater demonstrate the value of combining multiple geophysical techniques in areas where exposures are limited and invasive exploration is not an option.

Geologic control on the evolution of the inner shelf morphology offshore of the Mississippi barrier islands, northern Gulf of Mexico, USA

Between 2008 and 2013, high-resolution geophysical surveys were conducted around the Mississippi barrier islands and offshore. The sonar surveys included swath and single-beam bathymetry, sidescan, and chirp subbottom data collection. The geophysical data were groundtruthed using vibracore sediment collection. The results provide insight into the evolution of the inner shelf and the relationship between the near surface geologic framework and the morphology of the coastal zone. This study focuses on the buried Pleistocene fluvial deposits and late Holocene shore-oblique sand ridges offshore of Petit Bois Island and Petit Bois Pass. Prior to this study, the physical characteristics, evolution, and interrelationship of the ridges between both the shelf geology and the adjacent barrier island platform had not been evaluated. Numerous studies elsewhere along the coastal margin attribute shoal origin and sand-ridge evolution to hydrodynamic processes in shallow water (<20m). Here we characterize the correlation between the geologic framework and surface morphology and demonstrate that the underlying stratigraphy must also be considered when developing an evolutionary conceptual model. It is important to understand this near surface, nearshore dynamic in order to understand how the stratigraphy influences the long-term response of the coastal zone to sea-level rise. The study also contributes to a growing body of work characterizing shore-oblique sand ridges which, along with the related geology, are recognized as increasingly important components to a nearshore framework whose origins and evolution must be understood and inventoried to effectively manage the coastal zone.

A High-Resolution Geophysical Survey of Jenny Lake: Using Lake Sediments to Construct a Continuous Record of Tectonic Activity and Earthquake-Triggered Disturbances at Grand Teton National Park

The Teton Range, WY contains a legacy of late Cenozoic uplift and periodic Quaternary glaciations. Well-preserved fault scarps along the Teton fault displace glacier deposits from the most recent (Pinedale) glaciation and provide evidence for high fault activity during the past ~15,000 years. Observations of these scarps and previous field investigations indicate that postglacial fault offset occurred through a series of major, scarp-forming earthquakes. However, the postglacial paleoseismic record of the Teton fault remains incomplete. The goal of this project is to use lake sediments, contained in lake basins positioned on the fault, to construct a history of the timing and frequency of past earthquakes at Grand Teton National Park, and assess seismic impacts on diment erosion (e.g., landslides, debris flows, slope failures) and future hazard potential. Here, we report on multibeam sonar bathymetry and seismic reflection images from Jenny Lake, collected as part of an effort to identify glacial and tectonic landforms and to characterize infill stratigraphy. Our overarching objective is to combine these datasets with lake sediment cores from Jenny Lake and other nearby lakes to construct a continuous, accurately-dated record of past earthquakes and earthquake-generated slope failures in the Tetons.

Assessment of an ancient bridge combining geophysical and advanced photogrammetric methods: Application to the Pont De Coq, France

Abstract A high resolution geophysical survey was carried out on the Pont De Coq, a medieval stone arch bridge located in Normandy (France) in 2011 and 2012. Two complementary methods are used: Electrical Resistivity Tomography (ERT) and Ground PenetratingRadar (GPR). They allow to evaluate the structural state of the bridge and to characterize the subsurface around and beneath the bridge. An excellent correlation is obtained between the geophysical methods and the geological data obtained around the bridge. In order to improve the restitution of the geophysical data, an advanced photogrammetric method is performed, providing a high resolution 3D Digital Terrain Model (DTM) of the Pont de Coq. The advanced photogrammetry enhances the presentation of the GPR and ERT data. This approach is an easy-to-use, rapid and cost-effective tool for stakeholders. Finally, it is a promising and original method for improved interpretations of future geophysical surveys.

Holocene sediment distribution on the inner continental shelf of northeastern South Carolina: Implications for the regional sediment budget and long-term shoreline response

High-resolution geophysical and sediment sampling surveys were conducted offshore of the Grand Strand, South Carolina to define the shallow geologic framework of the inner shelf. Results are used to identify and map Holocene sediment deposits, infer sediment transport pathways, and discuss implications for the regional coastal sediment budget.The thickest deposits of Holocene sediment observed on the inner shelf form shoal complexes composed of moderately sorted fine sand, which are primarily located offshore of modern tidal inlets. These shoal deposits contain ∼67Mm3 of sediment, approximately 96% of Holocene sediment stored on the inner shelf. Due to the lack of any significant modern fluvial input of sand to the region, the Holocene deposits are likely derived from reworking of relict Pleistocene and older inner-shelf deposits during the Holocene marine transgression. The Holocene sediments are concentrated in the southern part of the study area, due to a combination of ancestral drainage patterns, a regional shift in sediment supply from the northeast to the southwest in the late Pleistocene, and proximity to modern inlet systems. Where sediment is limited, only small, low relief ridges have formed and Pleistocene and older deposits are exposed on the seafloor. The low-relief ridges are likely the result of a thin, mobile veneer of sediment being transported across an irregular, erosional surface formed during the last transgression.Sediment textural trends and seafloor morphology indicate a long-term net transport of sediment to the southwest. This is supported by oceanographic studies that suggest the long-term sediment transport direction is controlled by the frequency and intensity of storms that pass through the region, where low pressure systems yield net along-shore flow to the southwest and a weak onshore component.Current sediment budget estimates for the Grand Strand yield a deficit for the region. Volume calculations of Holocene deposits on the inner shelf suggest that there is sufficient sediment to balance the sediment budget and provide a source of sediment to the shoreline. Although the processes controlling cross-shelf sediment transport are not fully understood, in sediment-limited environments such as the Grand Strand, erosion of the inner shelf likely contributes significant sediment to the beach system.

Discovery of a new hydrothermal vent based on an underwater, high-resolution geophysical survey

A new hydrothermal vent site in the Southern Mariana Trough has been discovered using acoustic and magnetic surveys conducted by the Japan Agency for Marine-Earth Science and Technology's (JAMSTEC) autonomous underwater vehicle (AUV), Urashima. The high-resolution magnetic survey, part of a near-bottom geophysical mapping around a previously known hydrothermal vent site, the Pika site, during the YK09-08 cruise in June–July 2009, found that a clear magnetization low extends ∼500m north from the Pika site. Acoustic signals, suggesting hydrothermal plumes, and 10m-scale chimney-like topographic highs were detected within this low magnetization zone by a 120kHz side-scan sonar and a 400kHz multibeam echo sounder. In order to confirm the seafloor sources of the geophysical signals, seafloor observations were carried out using the deep-sea manned submersible Shinkai 6500 during the YK 10-10 cruise in August 2010. This discovered a new hydrothermal vent site (12°55.30′N, 143°38.89′E; at a depth of 2922m), which we have named the Urashima site. This hydrothermal vent site covers an area of approximately 300m×300m and consists of black and clear smoker chimneys, brownish-colored shimmering chimneys, and inactive chimneys. All of the fluids sampled from the Urashima and Pika sites have chlorinity greater than local ambient seawater, suggesting subseafloor phase separation or leaching from rocks in the hydrothermal reaction zone. End-member compositions of the Urashima and Pika fluids suggest that fluids from two different sources feed the two sites, even though they are located on the same knoll and separated by only ∼500m. We demonstrate that investigations on hydrothermal vent sites located in close proximity to one another can provide important insights into subseafloor hydrothermal fluid flow, and also that, while such hydrothermal sites are difficult to detect by conventional plume survey methods, high-resolution underwater geophysical surveys provide an effective means.

Stonehenge, Wiltshire, UK: High Resolution Geophysical Surveys in the Surrounding Landscape, 2011

An extensive high-resolution geophysical survey covering 2 km2was undertaken to the north of Stonehenge in June and October 2011. The survey is important in providing, for the first time, abundant detail on the form and structure of the Stonehenge Cursus, including the recognition of entrances in both of the long sides. Much additional information about the internal form of round barrows in the Cursus Round Barrow Cemetery, the course of the Avenue, the course of the so-called Gate Ditch, and numerous tracks and early roads crossing the landscape was recorded. A series of previously unrecognized features were identified: a pit-arc or cove below a barrow on the west side of King Barrow Ridge, a square-shaped feature surrounded by pits on the east side of Stonehenge Bottom, and a linear ditch on the same solstical axis, and parallel to, the southern section of the Stonehenge Avenue. An extensive scatter of small metallic anomalies marking the position of camping grounds associated with the Stonehenge Free Festival in the late 1970s and early 1980s raise interesting conservation and management issues.

A multi-method high-resolution geophysical survey in the Machado de Castro museum, central Portugal

Restoration of historical buildings is a delicate operation as they are often built over more ancient and important structures. The Machado de Castro Museum, Coimbra, Central Portugal, has suffered several interventions in historical times and lies over the ancient Roman forum of Coimbra. This building went through a restoration project. These works were preceded by an extensive geophysical survey that aimed at investigating subsurface stratigraphy, including archeological remains, and the internal structure of the actual walls. Owing to the needs of the project, geophysical data interpretation required not only integration but also high resolution. The study consisted of data acquisition over perpendicular planes and different levels that required detailed survey planning and integration of data from different locations that complement images of the surveyed area. Therefore a multi-method, resistivity imaging and a 3D ground probing radar (GPR), high-resolution geophysical survey was done inside the museum. Herein, radargrams are compared with the revealed stratigraphy so that signatures are interpreted, characterized and assigned to archeological structures. Although resistivity and GPR have different resolution capabilities, their data are overlapped and compared, bearing in mind the specific characteristics of this survey. It was also possible to unravel the inner structure of the actual walls, to establish connections between walls, foundations and to find older remains with the combined use and spatial integration of the GPR and resistivity imaging data.

Joint geophysical measurements to investigate the Rossano of Vaglio archaeological site (Basilicata Region, Southern Italy)

A high resolution geophysical survey was carried out in the archaeological site of Rossano di Vaglio (Basilicata Region, Southern Italy), where an important ancient sanctuary is located. It was built during the IV century B.C. and devoted to the goddess Mephitis. The sanctuary rises in an area affected by a multiple and retrogressive rototraslational landslide, historically and presently subject to reactivation. The main objective of this work was the identification of buried structures of archaeological interest in an area designated by the Archaeological Superintendence of the Basilicata Region. The study was performed by means of the use of high resolution geophysical surveys. In particular, we made use of the joint application of three highly sensitive and non-invasive geophysical techniques, namely the Geoelectrical, the Magnetic and the Ground Probing Radar (GPR) methodologies. In such a way, we obtained two important results: first, we provided the archaeologists with information about the limits of the areas to be excavated; second, we could verify in real time the reliability of the geophysical results. The experimental results showed four main magnetic anomalies in the area of study, in agreement with the GPR results obtained for the same target. Finally, a partial excavation test of the investigated area revealed a buried building structure, located in correspondence of an anomaly identified by means of the geophysical prospecting.

An integrated 3D constant offset GPR and resistivity survey on a sealed landfill — Ilhavo, NW Portugal

Abstract Owing to their nature landfills are challenging targets for high resolution Near Surface Geophysics. Herein it is described an integrated high resolution geophysical survey over the Ilhavo landfill sealed about a decade ago. The first aim of the survey is to investigate the time evolution of the contamination plume of the landfill since operations stopped and sealing took place. The second, and main objective, is the study of the landfill itself, that is, to carry out a high resolution 3D geophysical survey over it in order to investigate the thickness and effectiveness of the top cover, the thickness and sealing conditions of the landfill bottom and, finally, to investigate its internal structure. To fulfill these objectives an integrated 3D constant offset GPR and resistivity survey was designed. The interpretation of the geophysical data was carried out together with local borehole and hydrogeological information, so that, the ambiguity and uncertainty of the interpretation was reduced considerably and the usefulness of the methods were assessed.

Sonar de varredura lateral e sísmica de alta resolução aplicados no estudo de ecofácies na baía de Vitória - ES

Levantamentos geofisicos de alta resolucao e amostragem de sedimentos de fundo foram realizados na Baia de Vitoria tendo como objetivo mapear o fundo marinho acusticamente. A analise integrada de registros de sonar de varredura lateral e sismica rasa permitiu o reconhecimento de 4 ecofacies distintas. A ecofacies Tipo 1 esta associada a fundos sem penetracao do sinal acustico e com sonogramas de alta intensidade de retorno do sinal e dunas subaquosas, onde areias sao predominantes. A ecofacies Tipo 2 ocorre comumente em fundos areno-lamosos que apresentam alta penetracao do sinal acustico e baixa intensidade do sinal nos sonogramas. A ecofacies Tipo 3 e caracterizada por uma penetracao transparente do sinal ate encontrar um refletor de alta amplitude e sem penetracao, sendo tipica de fundos lamosos. A ecofacies Tipo 4 esta diretamente associada a fundos rochosos. A analise da distribuicao destas ecofacies permite a interpretacao dos principais processos sedimentares que atuam ao longo da baia.