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Near Surface 2009 - 15th EAGE European Meeting of Environmental and Engineering Geophysics
- Conference date: 07 Sep 2009 - 09 Sep 2009
- Location: Dublin, Ireland
- ISBN: 978-90-73781-72-6
- Published: 07 September 2009
1 - 20 of 139 results
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Comparison of Time-lapse GPR and Resistivity over Simulated Clandestine Graves
Authors J.K. Pringle, J.R. Jervis and G.T. TuckwellForensic geophysics should be an invaluable tool to assist search teams to detect and locate clandestine graves of buried murder victims. At present however, geophysics is under-utilised and currently used techniques may not be optimal for specific targets or sites. There is a need for geophysical datasets to be collected over known burial sites for varying time periods post-burial. A study site was created with a naked and wrapped pig cadaver. The dimensions are based on available statistics of discovered burials. Monthly surveys using resistivity, Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) were performed post-burial. Resistivity results show low anomalies over the naked pig and a smaller high anomaly over the wrapped pig with respect to background values. ERT time-lapse data shows optimum survey periods for the naked and wrapped pigs to be 9 and 3 months respectively. GPR 2D profiles detected both burials, with the wrapped pig exhibiting stronger reflection events. Lower frequency (110 MHz) antennae were found to be the optimal frequency to detect pig burials.
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High Definition GPR Surveys at the Roman Town Flavia Solva
Authors S. Seren, A. Hinterleitner, K. Löcker, P. Melichar and W. NeubauerAbstract High definition ground penetrating radar (HD-GPR) is defined as a GPR survey for archaeological prospection with a spatial grid smaller than or equal to 0.25 x 0.05 m. A comparison between a usual GPR survey with 0.5 m line distance and a HD-GPR survey is demonstrated with a large scale GPR survey at Flavia Solva (Styria, Austria). The Roman town Flavia Solva was founded in the early 1st century AD in the Roman province of Noricum and appears to have been destroyed during the Marcomanni Wars in the late 2nd century AD. The municipal area of the ancient town is located at the western bank of the river Mur and shows an extent of some 39 ha, partially destroyed by the modern town, roads and industrial zones. The use of HD-GPR explicitly enhances the quality of depth slices compared to a usual GPS survey. Therefore HD-GPR surveys will become a standard for archaeological prospection in Austria.
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Pricking Probe as a Complementary Technique in Archeological Prospecting
Authors S. Szalai, I. Lemperger, M. Pattantyús-Á and L. SzarkaWe present an original geophysical method, the so-called pricking probe, and demonstrate its usefulness in an archaeological prospecting study. By using this technique, we easily found in the subsurface the remnants of a Paleochristian sepulchral chapel, in spite of dense undergrowth. Later, in the same, already mopped-up area we carried out detailed and systematic pricking probe measurements, and also geoelectric, magnetic and georadar mappings. As we found in the given field experiment, the pricking probe technique is competitive to other methods, considering both its imaging and economic properties. It proved to be the first-second most powerful method. The main advantages of the pricking probe method are as follows. 1. its field procedure and data processing are simple, cheap and quick; 2. the method can be applied even among the most unfavourable field conditions (bad weather, extreme topography, dense undergrowth, etc.), 3. it is nature-friendly (the area has not to be mopped-out), 4. it is effective. Moreover, it provides complementary information to the geoelectric and georadar maps. On the basis of our experiments we recommend a combined application of the pricking probe technique and of one of the relevant standard geophysical method.
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Integrated Geophysical Surveys in the Tarragona Cathedral
Authors P.L. Cosentino, A. Casas, P. Capizzi, Y. Diaz, G. Fiandaca, E. Garcia, M. Himi, R. Martorana and R. SalaAn integrated geophysical survey has been conducted at the Tarragona’s Cathedral (Catalonia, NE Spain) with the aim to detect the existence of archaeological remains of the Roman’s temple devoted to August. Many hypotheses have been proposed about its possible location, the last ones regarding the inner part of the Cathedral, which is one of the most famous temple of Spain (12th century) evolving from Romanesque to Gothic styles. A project including electrical resistivity tomography (ERT), ground probing radar (GPR) and frequency domain electromagnetics (FDEM) has been planned over one year and conducted during a week of intensive field survey. From all the methods applied, both ERT and GPR have provided some detailed information on subsoil structures. The ERT method has been applied with different techniques and arrays, ranging from standard Wenner-Schlumberger 2D sections to full 3D electrical imaging using the MYG array. Electrical resistivity data have been recorded extensively and therefore, 70.000 apparent resistivity data were available to obtain a full 3D image after an integrated inversion. In conclusion, some significant buried structures have been revealed providing conclusive information for archaeologists.
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GPR Surveys in Urban Environment for Old Town Hall Remains Location in Lidzbark, Poland
By M. RudzkiThis paper presents the results of a GPR archaeological survey, carried out in urban environment, with the aim to confirm the existence and state of the remains of the medieval town hall in Lidzbark, Poland, destroyed during the big city fire in 1865. Today, an idea emerged to reveal its remains and expose it as a monument. As a guidance for subsequent excavation, and to to evaluate the suitability of the GPR method for all of the planned area, a GPR survey was carried out within a limited area, in the form of regular grid of 0.5 by 0.5 m size, with 250 MHz antenna. Generally, the GPR image of the underground structures turned out to be very close to the reality. Several types of events were observed and analysed, some of them being easy to mistake with real wall remains, and some of them imaging the buildings remains very truly. Especially, the time slices and 3D rendering techniques proved to be very helpful during the analysis. The survey results can be regarded as very promising for the rest of the total area planned for excavations.
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New Geophysical Electromagnetic Method of Archeological Object Research in Egypt
Authors O.A. Hachay, O.Y. Khachay and M. AttyaThe demand to the enhanced geophysical technique and device, in addition to the precise interpretation of the geo- physical data, is the resolution of the geophysical complex research, especially by the absence of priory information about the researched place. Therefore, an approach to use the planshet method of electromagnetic induction in the frequency geometry was developed by Hachay. et al., 1997a, 1997b, 1999, 2000, 2002, and 2005. The method was adapted to map and monitor the high complicated geological mediums, to determine the structural factors and criteria of the rock massif in the mine subsurface.
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3D ERT for the Study of an Ancient Wall Covered by Precious Mosaics
Authors G. Fiandaca, R. Martorana, P. Messina and P.L. CosentinoThe DC electrical tomography (ERT) is still a method scarcely diffused for the study of masonry of recent and ancient buildings, in spite of the very high resolution power of this methodology. The major limitation on ERT applicability on precious surfaces (like masonries or floors with fresco or mosaic covering) depends on the method of current injection: usually it is necessary to drive electrodes (small nails) into small perforations on the surfaces, to obtain sufficiently high current values (to produce good signal to noise ratio). An interesting application of the MYG array (that reduces significantly, compared to other classical arrays, the number of electrodes utilized for current injection) has been carried out on a wall of the fountain room of the Zisa Palace (Palermo, XII century A.D.), covered by a mosaic wall suffering important detachment of tesserae due to internal moisture. The results seem to suggest that ERT investigation with the MYG array has important applicative potentiality in study of precious walls or floors in artistic buildings, because of the low-invasivity and high resolution power as well as velocity of acquisition.
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Retrieving Consistent Initial Model for Surface Wave Inversion from Punctual a Priori Information
Authors D. Boiero, P. Bergamo and L.V. SoccoInversion of Surface Wave data suffers from solution non uniqueness and is hence strongly biased by the initial model. A priori geological information can be used to produce a reliable initial model: these information, however, are rarely available along all the survey line since they are mainly punctual information. Moreover, when we perform a laterally constrained inversion we have to be aware that bad quality data, though localized in a limited region of the entire dataset, can bias the whole result. In this work we present a procedure to estimate the quality of the Surface Wave dataset before the inversion and to produce a consistent initial model for the LCI. We prepared some tools to make the quality control of dataset semi-automatic: besides, we arranged a method to extend a priori punctual information to the whole survey line, in order to generate a pseudo 2D initial model able to make the inversion process more reliable. This method is based on a sensitivity analysis and on the application of scale properties of Surface Waves. Our procedure ensures a better model parameters estimation, makes the inversion process faster and allows a proper tuning of the strength of lateral constraints in LCI.
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Ambient Noise Cross Correlation Analysis of the Mas d’Avignonet Landslide, Isère, France
Authors F. Renalier, D. Jongmans, M. Campillo and P.Y. BardThe ambient noise cross correlation technique is applied to a landslide affecting clayey deposits. The 2-5 Hz frequency part of the Rayleigh wave group velocity dispersion curves obtained from cross correlation are completed up to 7 Hz by the ones computed from explosive shot signals. Local group velocity dispersion curves are derived by tomographic inversion, and inverted to obtain a 3D Vs image of the landslide. Despite the complex wave propagation in the Eastern part of the landslide and the sparse ray coverage, estimated velocities in the Western part and first order features are in good agreement with previous investigations.
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Blasting Induced vibrations – Prevision and Depiction by Means of Surface Waves
Authors L. Sambuelli, S. Foti, C. Comina, A. Callerio and A. CaleffiSurface waves play a fundamental role in the propagation of vibrations caused by quarry blasting since in the wave field generated from a shallow blasting source, most of the resulting vibratory energy is carried by Rayleigh waves that propagate close to the ground surface. Being the role of surface waves so pronounced both prevision methods and post blasting analyses should rely on a detailed study of this wave type in order to correctly understand the propagation phenomenon. In the present work a recently proposed relationship based on energy spreading in the form of Rayleigh wave is described evidencing its predictive capability in respect to data from a case history. The potentiality of surface waves parameters are moreover taken into account to better understand the influence of soil properties in respect to the measured vibrations and to underline the importance of dedicated soil testing in blasting sites.
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Relationship between Shear Wave Velocity and Undrained Shear Strength of Irish Glacial Tills
Authors M. Long, S. Donohue, P. O'Connor and P. QuigleyA large part of the city of Dublin it is underlain by a glacial deposit known as Dublin boulder clay (DBC). In engineering terms this lodgement till is characterised as being very dense / hard, of very high stiffness and of low permeability. The use of “Geobore S” rotary coring and Multichannel Analysis of Surface Waves (MASW) shear wave velocity profiling has improved our ability over recent years to adequately characterise this material. The main objective of this work was to explore the link between high quality laboratory strength tests on Geobore-S cores and MASW derived shear wave velocity measurements of Dublin boulder clay. A reasonably clear relationship was observed between these tests for three boulder clay sites.
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Characterization of a Concealed Fault Zone Using P and S-wave Seismic Reflection Data
Authors J. Carvalho, R. Ghose, C. Pinto and J. BorgesThe Vila Franca de Xira fault zone is the central sector of the OVLS fault zone, one of the major geological structures of the Lower Tagus Valley area in Portugal. Evidences previously gathered from geological and geophysical data suggest that it is an active fault zone and is responsible for the 1531 earthquake that caused extensive damages in Lisbon and the surrounding areas. However, no clear evidence of Quaternary seismic activity has been proven until now. The characterization of the fault zone in Holocenic terrains is therefore important for seismic hazard assessment. A P-wave and an S-wave seismic reflection profiles were acquired over an existing oil-industry and high-resolution P-wave seismic lines. The processing and preliminary interpretation of our data shows that S-wave data provides a superior resolution compared to the P-wave data and is the preferred geophysical method to characterize shallow faults zones in the study area. We have confirmed that faulting affects the Holocene alluvium and a vertical offset of 1-2 m was found in the S-wave data. This finding will allow a better definition of the return periods and the maximum expected earthquake magnitude of the OVLS fault zone.
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Comparing Shear Wave Refraction and Continuous Surface Wave Surveys in Sand and Gravel
Authors D.A. Gunn, G. Williams, M.G. Raines, J.D.O. Williams, P. Styles, V.S. Lane and S.M. ToonThe aims of this study were to evaluate some surface wave based methods and their limitations with regard to aggregate variability and thickness determinations. We compared the results of field assessments of sand and gravel sequences using two different surface wave survey approaches. The first, followed a seismic refraction approach, and the second, a CSW survey methodology. Further probing using an ultra-lightweight cone penetrometer provided verification of results, and also, an active extraction programme at the field site provided the opportunity to directly observe the subsurface geology post-survey.
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Using Shear-wave Velocity to Detect Void-induced Changes in Stress
Authors S.D. Sloan, R.D. Miller, M.H. McKenna and J.R. McKennaShear-wave velocity is directly related to stress; therefore, changes in stress may result in observable shear-wave velocity variations detectable using surface seismic methods. Shear-wave reflection and surface wave data were analyzed from multiple sites containing subsurface voids. Changes in shear-wave reflection velocity correlate to known subsurface conditions, including increased velocity over unstable voids with potential for roof collapse and decreased velocity over voids that have already experienced failure, forming sinkholes at the surface. Shear-wave velocity profiles inverted from surface wave data also show low-velocity anomalies with overlying high-velocity closures indicative of a subsurface void and associated increased stress on the supporting walls and roof rock. Shear-wave velocity may serve as an indicator of void presence and increased failure potential associated with stress build up, which may aid in public safety and remediation efforts in void-prone areas.
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Joint Land and Shallow-marine Seismic Investigations of Landslide Processes in the Bay of Trondheim, Mid-Norway
Authors U. Polom, J.S. L'Heureux, L. Hansen, I. Lecomte, O. Longva and C.M. KrawczykA combination of high-resolution shear-wave land-seismic and compressional-wave marine-seismic data was acquired to obtain information from the unconsolidated fjord-valley fill of the Trondheim harbour area, Norway. The sediments and overlying man-made fills were implicated in several near-shore mass-wasting processes, and land reclamation activities are still going on. A dense grid of high-resolution shallow marine seismics acquired over the prodeltaic sediments in the fjord was complemented by SH-polarized shear-wave reflection seismics on the land fill in the harbour. The shear-wave reflection seismic investigations achieved a highly resolved image of the fjord-valley fill, clear bedrock detection, and probably deeper structures. The bedrock surface is easily correlated between the marine (sleeve air-gun and sub-bottom profiling) and terrestrial seismic data sets. A few other major reflection events can be correlated between the land-seismic and the high-resolution marine data sets. This information enables shear-wave velocity calculation down to the bedrock and provides an indication of the stiffness of the sediments.
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The Use of Electrical Resistivity Tomography for the Characterisation of Voids in a Canal Embankment, Yorkshire, UK
Authors O. Kuras, R. Furner, C. Wooff and R.D. OgilvyAs part of an ongoing investigation into a leakage problem on the Aire and Calder Navigation in Yorkshire, UK, a geophysical study was undertaken in order to characterise voiding observed on a canal embankment near Whitley Bridge, Eggborough. Among other techniques, electrical resistivity tomography (ERT) surveys were carried out. 3D ERT over a known void using resistance data acquired at 0.5 m electrode spacing produced excellent results; key features such as the resistive void space, conductive base flow, and conductive zone of enhanced saturation below the void were imaged successfully within a local 3D resistivity model. Continuous 2D ERT along the embankment using a 2.5 m electrode spacing produced useful results, leading to the identification of potentially problematic locations along the walled section of canal. In conclusion, it appears that geophysical investigation of canal embankments of the type encountered at Eggborough is entirely appropriate and can produce information that would otherwise be impossible to obtain. We were encouraged by the ability of ERT to characterise and delineate existing voids and zones of increased saturation within an embankment and identify possible problematic areas.
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Geophysical Investigation for the Rehabilitation of a Flood Control Embankment
Authors E. Cardarelli, M. Cercato and G. Di FilippoTo comply with recently published seismic regulations and environmental standards, existing dams and embankments are now being examined for maintenance, repair or rehabilitation. Engineering geophysics is almost the only viable option for investigating these structures and the underlying soil as a whole system. In this contribution, electrical and seismic investigations are performed on an outdated flood control embankment, that has to be put again into service. Geophysical investigation has proven successful to determine the relevant properties of the embankment and the main geometrical features of the underlying subsoil, serving as an important guidance for the rehabilitation intervention.
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3D Seismic Imaging Using Numerical Modeling for Embankment Dam Stability Analysis
By P.C. SirlesThe paper represents the first time that 120-channel, full 3D refraction seismic data have been acquired, processed and presented in a numerical model. Sinkhole development on a high-risk dam required the use of an advanced 3D seismic technique to aid the engineers in definition of the problem, and provide information for remediation. The data and results were just released for publication. The High-Resolution Engineering Seismic Studies (#10) would be an optimal session to present a new - 3D Engineering Seismic - technology developed in the last 2 years. {FYI - I am aware the abstract submitted herein is NOT complete, or in your template format! I have asked for a preliminary review, and will complete IMMEDIATELY if the topic is acceptable, and their is potential for acceptance. I could not prepare or submit anything earlier, as the results were confidential - I FINALLY got approval to present this case study! I did have an email discussion with Ms. Sandra Hermus, Conf. Coordinator. Thank you for consideration, as I (Zonge) will be there as an exhibitor; as such, I would love to present this new technology.}
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Geophysical Characterisation of Glacio-fluvial Gravels – A Case Study from Cork, Ireland
Authors S. O'Connor, S. Donohue, M. Long and P. O'ConnorExtensive glacio-fluvial deposits occur within Cork city and its surrounds. The glacio-fluvial gravels are of mixed provenance and thickness due to the complex geology of the area. In this paper, Electrical Resistivity Tomography (ERT) and Multichannel Analysis of Surface Waves (MASW) methods were tested simultaneously on a site with existing geotechnical and Standard Penetration Test (SPT) data. The combined use of both methods has potential, with ERT approximating material type recorded in boreholes and shear wave velocities from MASW predominantly corresponding to densities identified by SPT.
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Joint Seismic and CPT Studies of the Sliding Loess Wall along the Danuber River at S-Hungary
Authors A. CS. Kovács, L. Zilahi-Sebess, T. Bodoky, T. Gúthy, E. Hegedus and R. CsabafiA 30 to 35 m wide slice of a 100m height loess wall sank more than 10 m at the bank of the Danube near Dunaszekcső (Hungary) on 12th of February, 2008. Eötvös Lorand Geophysical Institute (ELGI) was requested a geophysical investigation of the area. ELGI deployed a system of six continuously operating seismic stations to observe the seismic micro-emissions. Two main source areas of seismic micro-emission were allocated after the data analysis. We made four points of CPT a depth of 12 m on the bank of the Danube and we have concluded that the movement of the loess wall was caused not by a sliding phenomenon. We used 121 units of RefTek 125 single channel autonomous seismic recorder and a vibrator as a source to make two seismic lines beneath and above the loess wall. Based on the structural imagefrom seismic tomography and reflection sections sedimentary layers of different thicknesses can be found on the old basement up to the level of the river Danube. The anomalies of the two profiles mark out a tectonic zone running in an approximately E-W direction.
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