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Near Surface Geoscience 2014 - 20th European Meeting of Environmental and Engineering Geophysics
- Conference date: September 14-18, 2014
- Location: Athens, Greece
- Published: 08 September 2014
121 - 140 of 185 results
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Squared-slowness Gradient Profile from Surface-wave Inversion as a Starting Model for Full-waveform Inversion
Authors A.V. Ponomarenko, V.V. Kazei, B.M. Kashtan, V.N. Troyan and W.A. MulderSummaryFull-waveform inversion (FWI) is widely used for the detailed reconstruction of subsurface velocity models from seismic data collected in different environments. The method requires an adequate starting model. Otherwise, an incorrect model may be obtained, due to the presence of local minima in the least-squares objective function. This is in particular true in case of a complex near-surface velocity structure. Classic surface-wave inversion provides a layered representation of the medium, which can subsequently be smoothed to serve as a starting model for FWI.
As an alternative to the layered representation of the medium, we consider a continuous, smoothly varying P-wave velocity profile. The profile has its squared slowness increasing linearly with depth and allows for analytical evaluation of the dispersion curves. We investigate the application of the reconstructed profile as an initial guess for acoustic FWI.
A synthetic example shows how we can reconstruct both the background structure as well as a high-velocity inclusion in this way.
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Investigation of Pedogeophysical Relationships Using in Situ Measured Electrical Resistivity and Soil Physical and Root
More LessSummaryElectrical resistivity tomography (ERT) is one method for mapping and monitoring of the vadose zone. However the relation between the sensed physical properties (e.g., resistivity) and the soil parameter of interest is ambiguous and often not or only poorly understood. This study was carried out to quantify soil properties and the distribution of roots in a soil profile under field conditions at different time steps during the vegetation period. In our abstract we will focus on the investigation of pedogeophysical relationships between soil physical and plant physiological properties and electrical resistivity. The relationship with soil water content varies with the time (root growth). At both time steps we find a nearly constant medium correlation of electrical resistivity and root parameters.
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Building 3D Geomorphological Models from Legacy Resistivity Data in the Kabul River Valley, Pakistan
More LessSummaryThrough the application of modern geostatistical analysis and inversion techniques drawn from contemporary seismic interpretation methods a number of 1D resistivity data have been re-modeled and visualized in 3D space. The resultant model extends the original interpretation of the data to depict alluvium layers as lithological and structural units within the bedrock. By tuning the variogram parameters used in this approach it is possible to visualize the individual lithofacies and geomorphological features in the subsurface rock units. In this study an electrical resistivity data set collected in the 1980’s as part of a groundwater study in an area of the Peshawar basin of Pakistan has been re-examined. Limited borehole log data have been combined with local outcrop information to calibrate the data.
The Himalayan orogeny has uplifted and generated significant faulting in the bedrock of the area resulting in the formation of several clay-filled depressions. Paleo-streams have reworked the clays and the resultant sediments have been deposited as prograding fan shaped bodies and lacustrine deposits with inter-layered sand-gravel and clay-silt facies. The Naranji area aquifer has thus formed as a result of local tectonic activity with fluvial erosion and deposition and is characterized by coarse sediments with high electrical resistivities.
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Using Electrical and Seismic Tomography to Detect Weak Points on a Potash Mining in Central Germany
Authors K. Duennbier, J. Confal, T. Schicht, K. Thiemann and F. BoernerSummaryThe objective is to develop a combination of geophysical and petrophysical methods for non-invasive characterization of a potash mining dump. It includes tomographic methods such as geoelectrics and seismics as well as grounds penetration radar (GPR), spectral induced polarization (SIP) and nuclear magnetic resonance (NMR). The resulting geophysical models help to detect and display weak areas due to, for example, abnormal strengths, hydraulic permeability and water content. The 2D and 3D underground models of the electrical resistivity tomography and the seismic refraction survey are combined with the results from the petrophysical data of SIP and NMR as well as p-wave velocities depending on water content, porosity and composition.
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Time Lapse ERT Monitoring of Olive-oil Mills’ Wastes (OOMW) Using Simulation and Experimental Data
Authors S. Kirkou, P. Tsourlos, N. Papadopoulos, P. Soupios and J.H. KimSummaryOlive oil production is one of the most important activities in the Mediterranean area and in Greece in particular. Olive oil production generates a large volume of liquid wastes which can cause severe pollution due to the high organic and in-inorganic load that they convey. In this work we assess the ability of time-lapse electrical resistivity tomography (ERT) technique to monitor Olive-oil mills’ wastes (OOMW) movement into an aquifer. Test involve performing extensive synthetic modelling using computer generated models for cross-hole ERT arrangements and applying various 4D time lapse inversion processing to the monitoring data. Further, 4D time lapse inversion was performed to cross-hole ERT data obtained during a tank experiment which involved simulation of OOMW movement into a saturated aquifer. Results validate the applicability of cross-hole time lapse ERT to monitor OOMW movement and help to decide ways for optimum data processing and collection.
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Time-domain Spectral Induced Polarization and Magnetics for Mapping Municipal Solid Waste Deposits in Ghana
Authors D.D. Wemegah, G. Fiandaca, E. Auken, A. Menyeh and S.K. DanuorSummaryEnvironmental pollution from solid waste landfilling is a serious risk for groundwater and downstream surface water, especially when landfilling is carried out unengineered, with no protective layer underneath the waste deposits. Most research in Ghana and in other developing countries on unengineered landfills depend almost exclusively on hydrochemical and geochemical analysis, which is not necessarily representative of the entire dumpsite catchment area. For this reason, integrated and cost effective geophysical methods, namely DC electrical resistivity, full waveform time-domain induced polarization and ground based magnetic measurements were employed to map and characterize four dumpsites in the Kumasi Metropolis, the seconds most populated city in Ghana. The results of one site, namely the decommissioned Ohwim waste dumpsite, are presented. The magnetic surveys helped in the mapping of the lateral extent of the waste deposit. The DC /full wave induced polarization tomography on the other hand mapped the vertical extent of the dumpsite and characterized the hosting geology. Furthermore, some regions were identified, where a pollution plume is likely to be present.
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Geoelectrical Monitoring of a Decommissioned Landfill in Thessaloniki (N. Greece)
Authors G.N. Vargemezis, P. Tsourlos, I. Fikos, G. Tsokas and N. KazakisSummaryIn this work we present an ERT monitoring case study in the Derveni Landfill (Thessaloniki, N. Greece). The landfill was subjected to reclamation in 2006, but recently, leakage of water polluted with leachate was observed. In order to investigate the problem a dense network of 2D ERT measurements was carried out at larger scales. In this work the results of the time-lapse ERT measurements obtained over this area are presented. Despite the lack of permanent monitoring installation the repeated time-lapse ERT data illustrate that, even at relatively sparse time intervals, they can provide high value and low cost information which is valuable for evaluating the overall progress of the remediation process.
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Cavity Investigation by Surface Wave Tomography and Microgravity
More LessSUMMARYAn integrated geophysical approach for detecting cavities was applied experimentally to an abandoned underground quarry network in cretaceous chalky limestone located in in Souzay-Champigny. Microgravity evidenced negative anomalies corresponding to known conduits and identified the probable extensions of this network in unmapped areas. Microgravity, conducted with low spacing and careful implementation in order to ensure high resolution and accuracy, remains, one of the methods most suited to the detection of voids, even relatively small, in the first 20m of depth. Its weakness lies in its ambiguities of interpretation
The surface wave tomography, that analyses the Rayleigh wave propagation, contributes at reducing these ambiguities, by characterizing the mechanical behavior of the gravity anomalous zones
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Reconnaissance Geophysical Survey for the Detection of Salinization and Stratigraphy in Thorikos Valley, Attica, Greece
Authors G. Apostolopoulos, A. Kallioras, K. Pavlopoulos, K. Stathopoulou and A. VlassopoulouSUMMARYA reconnaissance geophysical survey is a starting task of a multitasking collaboration to detect all hydrogeological (extent of salinization), stratigraphical, geological features of Thoriko valley in order to reconstruct the environment in ancient times as well as to interpret the position of the various archaeological monuments existing in the area. Electromagnetic measurements with conductivity meter, made in a quick mode with a cart dragged by car, have given, after data evaluation and filtering, valuable information regarding near surface salinization phenomenon. In addition ERT and IP profiles give deeper detection of this phenomenon discriminating media of various clayey content.
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The Application of Resistivity and EM Method to Monitor Vinasse Infiltration in Sandy Sediments
Authors W. Malagutti Filho, J.R.M. Bortolin, C.A. Moreira and A.M. PereiraSUMMARYThe cultivation of sugar cane represents one of the most important agricultural supplies in Brazil. One one of its driving factors is the production of etanol, a widely used fuel for Brazilian automobiles. Among the residue related to the production of etanol, the vinasse is highlighted, a liquid substance generated in the ratio of approximately 13 liters to each liter of etanol that is produced.
This paper proposes to identify the geophysical signature related to controlled vinasse infiltration in sandy sediments, as well as to monitor the contaminated plume through the use of investigational electrical resistivity and electromagnetic geophysical methods.
The study was performed on a 100m2 (10m × 10m) rural area near the municipality of Corumbataí, inland Sao Paulo State, Brazil, in sandy sediments from Pirambóia Formation.
Two trenches of approximately 0,45m × 0,45m × 2,00 (total approximate volume of 405 liters) were excavated in the area to receive the vinasse infiltration.
The electrical measurements were carried out in two separate rounds: before and after excavating the trenches and infiltrating the vinnase.
The observed anomalies presented low resistivity in the ER method and the anomalies shown by the EM method, they can be conductive or resistive, depending on the investigated depth.
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A Seismic Processing Approach Dedicated to Quantitative Characterization of Landfill Heterogeneities
Authors L.A. Konstantaki, R. Ghose, D. Draganov, G. Diaferia and T. HeimovaaraSUMMARYThe ability to image and quantify the heterogeneity in municipal landfills is crucial for improving the landfill treatment methods, for predicting the behaviour of processes that take place inside the landfills and hence, for estimating the after-care period. Our aim is to image the flow paths inside landfills and to quantify the heterogeneity. We develop a new methodology using both seismic reflection and electrical resistivity methods. We illustrate the possibility of imaging wet and dry pockets inside a landfill and provide density and porosity distributions that are important input parameters to models that predict the behaviour of landfills.
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Geophysical Detection of Underground Voids - Ocna Dej Salt Mine (Romania)
Authors D. Ioane, F. Chitea, C. Marunteanu and M. MezincescuSUMMARYActive subsidence followed by collapse of shallow geological structures occur in areas with old abandoned mining works in salt bodies, due to the dissolution processes developed in salt by fresh ground water.
The active subsidence started beneath a new building in the salt mine Ocna-Dej area was not possible to be stopped using geotechnical and hydrogeological techniques. Detailed resistivity and gravity investigations were employed to detect the underground cause of the building subsidence.
VES data succeeded to illustrate the location of large underground voids in the salt body along faults or in places where the exploitation chambers roof or pillars were damaged by dissolution processes. The gravity data were interpreted in the new frame offered by detailed resistivity imaging, contributing to the evaluation of collapse hazard in the Ocna Dej salt mine area.
The interpretation of the gravity and resistivity data showed that the highest hazard for collapse in the Ocna Dej salt mine is in areas where the walls separating the bell-shaped and rectangular exploitation chambers were already dissoluted, resulting larger underground voids, and along faults crossing the salt body on its entire vertical development, with very active dissolution processes.
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A Geophysical Insight for the Occurrence of Mediterranean Temporary Ponds on Mts. Oiti and Kallidromo (Greece)
Authors J.D. Alexopoulos, S. Dilalos, E. Vassilakis, D. Michelioudakis, S. Mavroulis and P. FarangitakisSUMMARYA geophysical survey was performed at selected locations of Mt. Oiti and Mt. Kallidromon characterized by the hosting of priority habits of Mediterranean temporary ponds and the threatened plant species of Veronica oetaea, in order to understand the geoenvironment and contribute to the conservation of biodiversity. Primarily, the formation of these seasonal ponds, where Veronica oetaea occurs, seems to depend exclusively on the local hydrogeological regime. Thus, we investigated the subsurface structure of “Livadies” and “Nevropolis” ponds with the application of Electrical Resistivity Tomography for high accuracy information and Vertical Electrical Sounding for deeper data acquisition. Four ERT sections and 15 geoelectrical soundings in total were carried out. The combined results of their processing revealed differences at the geological structure beneath the ponds locations. At “Livadies” pond (Mt. Oiti), two geoelectrical layers were distinguished both corresponding to a folded flysch succession, contributing to the formation of this pond. On the contrary, at “Nevropolis” pond two geoelectrical layers were identified and interpreted as a surficial soil deposit stratum covering the geomorphological karst structure of a polje, created on the underlying limestones. The combined geophysical research offered significant data for the formation and the hydrogeological status of the priority habitats.
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Advanced Geophysical Methods for Diagnostics of a CH Contaminated Site
Authors Z. Plank, J. Stickel, G. Taller and B. KerekSUMMARYSoil contamination should be avoided, but if this was the case there are several methods for delineation. Recently sophisticated developments have taken place in certain geoelectrical survey technologies that allow direct detection of some contaminants under the surface as well. Also some certain developmmnet in CPT technology gives effective tools in order to provide reliable geological information on contaminated sites.
This paper aims to present new results on methodological research on the application of advanced geophysics and up to date technologies in environmental diagnostics.
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Attenuation of Oil Pollution as Observed by VES Monitoring Program
More LessSUMMARYOil pollution is known to be among the environmental problems which cause long – term negative effects on soil and underground water.
Crude oil can be framed into light-non-aqueous-phase-liquids class (LNAPL), having a density lower than the water. Its mixture with water can be achieved in special conditions of temperature and pressure. When oil products reach the ground water, three pollution phases results:
- Separated Hydrocarbons Phase (PSH) – forms a layer or lenses of hydrocarbons, floating on the top of water
-Dissolved Phase Hydrocarbons (PDH) – resulted from hydrocarbons soluble fractions
-Volatile Phase Hydrocarbons (PVH) – resulted from oil volatile compounds
Standard analyses for monitoring an oil contaminated area consist in measuring the volatile compounds and hydrocarbons soluble fractions. As such a monitoring program requires financial effort, a less expensive and faster monitoring program was tested. By using noninvasive electrical resistivity investigation method repeated at a interval of 5 months, attenuation of oil polluted area could be observed. Electrical resistivity results were confronted with BTEX and HC results from water probes, showing good applicability of VES in investigation oil-pollution environmental problems.
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Seismic Characterization by Inversion of HVSR Data to Improve Geological Modelling
Authors R. Martorana, P. Capizzi, G. Avellone, R. Siragusa, A. D’Alessandro and D. LuzioSUMMARYAn application of HVSR inversion is presented in order to verify the effectiveness of this technique for purposes of geological reconstruction of the subsoil finalized to studies of seismic microzonation of heavily urbanized areas, where few stratigraphic and geophysical constraints are available and most of the information are derived from the geological maps. In such cases the uncertainty of the results is is enhanced by doubts on the nature of the H/V peaks, not always caused by stratigraphic discontinuities, and to the subjective choices done especially in the step of signal preprocessing.
The investigated area (Altavilla Milicia, Sicily) includes the town center and the adjacent coastal plain, characterized mainly by outcrops of marine terraces and continental Pleistocene deposits that do not indicate directly the oldest geological formations, which, however, outcrop in the surrounding areas. However in order to constrain the inversion of the HVSR curves we uses only the detailed knowledge of the geological formations outcropping in the surrounding area and of the tectonic history, together with the typical seismic velocity of the formation outcropping in the area. In spite of this two geological sections have been constructed, showing the main pattern of geological formations and tectonic structures.
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Centroid-based Cluster Analysis of HVSR Data for Seismic Microzonation
Authors P. Capizzi, R. Martorana, G. Stassi, A. D’Alessandro and D. LuzioSUMMARYHorizontal to Vertical Spectral Ratio (HVSR) datasets acquired for studies of seismic microzoning in various urban centers of Sicilian towns, have been used to test clustering analysis through a non-hierarchical centroid-based algorithm. In this context clustering techniques may be useful to identify areas with similar seismic behaviour through HVSR data.
Centroid-based algorithms generally require the number of clusters, k, and the initial centroid coordinates to be specified in advance. This aspect is considered to be one of the biggest drawbacks of these algorithms. The proposed algorithm doesn’t limit the number of k clusters and choose the initial centroids automatically from the data set.
Azimuthal variation of the H/V peaks was also taken into account. Finally different partitions obtained using the centroid-based algorithm were superimposed on the geological map of the analyzed sites to identify possible correlations with geology and topography.
The obtained results underline how the most appropriate clustering algorithm for a particular site often needs to be chosen experimentally. In fact in many cases the choice of the partition is strongly linked to the choice of parametric distance and to geological knowledge, while in other cases, the results showed similar results regardless of a priori choices.
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Determination of Ground Predominant Period and H/V Ratio by Single Station Microtremor Records in Trabzon (Arsin)
More LessSummaryMicrotremor method used for engineering seismology is very important for determining of dynamic ground parameters and its variations. Method based on frequency of horizontal and vertical component microtremor records provides to quick and economical estimation of dynamic ground parameters. The most important advantage of Nakamura method defined as single station method does not require reference point and it can be applied easily in the area with low seismic density and without base rock. In this study, Nakamura (H/V) spectral ratio method has been applied to microtremor records taken with CMG-6TD three component broad band velocity seismometers at 116 points with the aim of determining ground predominant period and magnification parameters in the study area. Maps of predominant period and H/V ratio of the study area are created by derived values.
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Importance of Simulating Realistic Transducers in GPR Numerical Modelling
Authors N. Diamanti, J.D. Redman and A.P. AnnanSummaryGround penetrating radar (GPR) is a very powerful, non-destructive testing tool with a wide range of applications mainly associated with shallow depth exploration. The complexity of the subsurface leads to complicated GPR images and also, attempting to use experimental measurements to assess and simulate complex problems is costly and time consuming and often limited by availability of suitable materials. The latest advances in GPR modelling provide an effective means for assessing GPR responses and now GPR models are becoming fully three-dimensional and sophisticated. Representative models can require large amounts of computer power and memory with very long run times. On the other hand, modern computing capacity is increasing so rapidly that problems previously considered impractical can be modelled for real application projects. One of the trade-offs in numerical modelling is the rational of using point sources and receivers versus full antenna structure simulations since the former require less computer memory and computation time. In this paper, we explore the question: when is a detailed GPR antenna model needed and when do point sources suffice?
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Evaluation of EMD-based Methods on GPR Data
Authors M. Manataki, A. Vafidis and A. SarrisSUMMARYEmpirical Mode Decomposition (EMD) is a relatively new technique for analysing non-linear and non-stationary time series. Ensemble Empirical Mode Decomposition (EEMD) and Complete Ensemble Empirical Mode Decomposition (CEEMD) are noise assisted and adaptive methods based on EMD. Here, we compare the empirical mode decomposition methods using both synthetic and real GPR data. In particular we examine: (1) the separation of high frequency wavelets from the low frequency ones and (2) the noise level that yields better decomposition for EEMD and CEEMD. We also examine the capability of these decomposition methods to remove random and coherent noise on real GPR data.
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