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Near Surface Geoscience 2013 - 19th EAGE European Meeting of Environmental and Engineering Geophysics
- Conference date: 09 Sep 2013 - 11 Sep 2013
- Location: Bochum, Germany
- ISBN: 978-90-73834-38-5
- Published: 09 September 2013
61 - 80 of 116 results
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Shear Wave Aquiclude Survey and Interpretation
By H.P. MuellerExamining, processing and mapping of an aquiclude zone at some 10 to 15 m target depth in an urban environment by SH-wave recording using a mini vibrator as a source is presented. The aquiclude's top depth, only indicated before at a monitoring well, had to be mapped throughout the seismic line. The layout in the street demanded 2D crooked-line processing. In the seismic section a remarkable two-sided step-down of some 2 m height within 20 m distance was observed which made interpretation difficult. This result could only be validated by combining surface profiling with VSP survey information at the well location. Evidence can be stated now, as two additional wells, recently drilled on the very surface line, being the subject of this presentation, found the aquiclude as predicted by the seismic forecast. The seismic model constitutes concluding evidence of pre-glacial scouring here. Setting out the necessity to benefit from both methods in the attempt to identify the aquiclude's layer surface, is claimed here. To gain optimized constraints in designing the SH surface line to follow, it is proposed to perform SH VSP first if wells in the vicinity were available.
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Seismic and Geoelectric Investigation of Historical Mining Structures - A Case Study
Authors U. Swoboda, S. Uchtmann, K. Limbrock, R. Elsen, D. Orlowsky, K. Telenga, A. Koschare and F. WollnikThe Ruhr area is the biggest urban agglomeration and is well known for its coal mining activities. In consequence of the former underground mining numerous artificial caves near to the surface can be found. These caves lead to earth drops and sinkholes which form a safety hazard for the environment. In this presentation a case study of a geophysical investigation will be shown whereat seismic and geoelectric methods were applied close to an area where several historic coal mines were placed. Six survey profiles were planned whereas five were mainly parallel and one perpendicular to a main geologic fault. The survey lines had an overall length of approx. 1000 m and covered a region of 14 000 sqm. The seismic data were analyzed using the following methods: standard refraction processing (wavefront method), refraction tomography, single shot analysis for gaps in the refracting waves, reflection processing and tomographic velocity analysis of the transverse travelling surface waves. The geoelectric data were processed using a 2-D inversion approach. All processing methods showed a number of anomalous zones. It became visible that the anomalies form several clusters which can be interpreted as second order fault positions with a typical appearance for wrench faults.
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Geophysical Investigation of a Burning Dump in Estonia – A Case Study
Authors S. Uchtmann, O. Brenner, U. Swoboda, R. Elsen and D. OrlowskyA burning semi-coke dump site at Kohtla-Järve, Estonia has been investigated by geophysical methods. The aim of the project was to test the capability of seismic and electromagnetic surveys to detect former or active burning zones. The results of the seismic and electromagnetic measurements show different characterizations of the investigated area. As both geophysical methods are based on distinct physical principles, the results are different. The seismic investigation is based on the propagation of elastic waves in the subsurface, which is mainly influenced by discontinuities in the ground like cracks and weak zones, changes in the texture of the ground or cavities. The seismic results, processed with a focus on surface waves, show approximately 20 anomalous positions with a punctual appearance. The results of the electromagnetic survey correlate with the observations at the surface. It is assumed, that hot spots of the burning dump can be detected with electromagnetic measurements. During the field survey two of the reported seismic anomalies were mechanically excavated. At both positions the results of the survey are verified.
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Integrated Geophysical Investigation at a Construction Site in a Highly Urbanised Area
By F. BahloulTechniques to investigate the shallow underground with the help of a combination of several geophysical methods increased rapidly during the last decade. Nevertheless, the use of different geophysical methods results often in different interpretations of the investigated area. This paper deals with the integrated interpretation of CMP-refraction seismic, refraction tomography, traditional refraction seismic, electric resistivity tomography and borehole logging data acquired at a construction site in a highly urbanized area (Makkah, Saudi Arabia). Objectives of the geophysical measurements were mainly to determine und characterise the thickness of the saturated zone, the depth of the groundwater as well as the depth of the bedrock. All geophysical results (seismic tomography, resistivity and borehole logs) are combined and joint interpreted together with the data from the given boreholes in order to calibrate the final interpretation result. Interpretation has been performed with the state of the art interpretation and modelling software PETREL (Schlumberger Information Solutions) according to international industry standards. The chosen interpretation system ensures the generation of exact and consistent spatial images of the underground conditions.
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On Inversion of Frequency Domain Electromagnetic Data in Salt Water Problems - Sensitivity and Resolution
By T. GüntherFrequency domain electromagnetics (FDEM) is a fast investigation method for large scales and can particularly be helpful in salt-water problems. Sensitivity studies and simple models show the dependence on geometric factors and noise levels. Methods of resolution analysis can be successfully applied to reveal uncertainties of the model parameters and interdependence of the data. A combination of electromagnetic and direct current data significantly improves the results and their reliability. The methods are demonstrated on synthetic data and field data from a coastal aquifer system.
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1D Joint Inversion Analysis of VES and TDEM Soundings at Termas de Ibirá Region, Paraná Basin, Brazil
Authors M.A. Couto, J.L. Porsani, C.A. Bortolozo and D.N. LeiteIn this work, the authors present results of 1D joint inversion of Vertical Electrical Soundings (VES) and Time Domain Electromagnetic (TDEM) soundings at Termas de Ibirá region, countryside of São Paulo State, Brazil. The objective is the analysis and comparison of the results of individual inversion and joint inversion. The VES results can solve the shallow layers (until the depth of 100 m) and the TDEM results solve the deep layers (between 100 - 1000 m depth). Therefore, the joint inversion explore the best of each method and it allows to make a more reliable interpretation about the local geology. Keywords: TDEM, VES, Joint inversion, Paraná basin, Termas de Ibirá, Brazil.
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Geoelectrical Characterization by VES/TEM Joint Inversion at Urupês Region, Paraná Basin, Brazil
Authors J.L. Porsani, D.N. Leite, C.A. Bortolozo and M.A. CoutoThis paper shows the results of joint inversion of VES/TEM for Urupês region, Paraná sedimentary basin, São Paulo State, Brazil. The objectives of this research were to map the Adamantina Formation (sedimentary aquifer) and to locate fractures zones in the basalt layer of the Serra Geral Formation. The results indicate the tick of the Adamantina Formation (Bauru aquifer) and the fracture zones in the basalt of the Serra Geral Formation. Keywords: VES, TEM, Joint inversion, Paraná basin, Urupês, São Paulo State, Brazil.
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Automated Electrical Resistivity Tomography Monitoring of Quarry Dewatering
Authors J.E. Chambers, P.I. Meldrum, P.B. Wilkinson, B. Matthews, O. Kuras, D.G. Gunn, S. Uhlemann and L. OxbyA study has been undertaken to demonstrate proof-of-concept for the use of time-lapse ERT for the monitoring of changing groundwater conditions at mineral extraction sites undergoing active dewatering using a well-point system. Monitoring was undertaken using a permanently installed geoelectrical imaging system, which comprised an advanced data logger (referred to here as “ALERT”) capable of the autonomous collection of geoelectrical data, and a network of surface electrodes. ALERT monitoring is demonstrated as an effective means of monitoring groundwater rebound and drawdown, although a time-lag is observed between hydraulic head levels recorded in the piezometers and the bulk saturation information provided by ERT.
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Long Electrode ERT for Salt Water Monitoring - Modelling, Sensitivity and Resolution
Authors T. Günther, M. Ronczka and C. RückerThe upward surge of saltwater due to a high extraction rate of water plants, tectonic weakness zones or eroded clay layers threatens the fresh water supply in some regions of northern Europe. For monitoring the movement of salt water, the usage of borehole measurements is insufficient as only point information can be retrieved. Our aim is to develop a monitoring system that uses boreholes as electrodes (Long Electrode Electrical Resistivity Tomography - LEERT) in conjunction with surface-electrodes. As a first step we conducted synthetic modelling using the Finite Element Method and the Complete Electrode Model in order to obtain a better insight on the influence of long electrodes ERT measurements. Sensitivity and resolution measures show a reasonable capability of imaging saltwater intrusions if surface electrodes are used in combination with boreholes.
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ERT Survey for Characterising the Subsurface of a Golf Course Build over the Edge of a Volcanic Caldera (Canary Islands)
Authors A. Casas, E. Estévez, R. Lovera, J.C. Tapias, M.P. Palacios-Díaz, M. Himi and M.C. CabreraKnowledge of geometry and hydraulic properties of the unsaturated zone is essential to assess the dynamics of the subsurface drainage of water that seeps from the ground surface, whether it is rain water as excess of irrigation. This interest increases when irrigation is conducted with reclaimed water, as it happens on the golf course of Bandama which since 1976 is being watered with reclaimed water from the wastewater treatment plant (WWTP) of the city of Las Palmas de Gran Canaria. The golf course of Bandama is located on the edge of the volcanic caldera of the same name and occupies an area approximately 30 hectares of which some 14.5 ha are irrigated by sprinkling. This work arises to determine the characteristics of the subsoil under golf course by electrical resistivity tomography method, with particular interest in trying to delimit the areas of preferential drainage affecting vulnerability to contamination of the underlying aquifers.
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Electrical Resistivity Tomography at the Search of Groundwater on the South of Russia
Authors V.A. Shevnin, D.A. Kvon, B.A. Nikulin, A.A. Ryjov and A.D. SkobelevDue to shortage of fresh drinking water near Anapa town (near Black Sea), geophysical investigations were performed for searching and mapping aquifers in the area, where, according to rare wells exist probability to find fresh underground water. Geophysical survey was carried out with Electrical Resistivity Tomography (ERT) and water resistivity measurements. The resistivity of fresh groundwater is 15 Om.m, its salinity is 0.4 g/l. We calculated rocks resistivity taking into account groundwater salinity and concluded that basement rock is limestone not marl. This conclusion was supported by roentgen-radiometric measurements of rock samples estimating 85% of CaCO3 content. When petrophysical model of rocks was determined we found boundary values of resistivity for fractured water-saturated limestone, gravel and sand and these isolines put on geoelectrical cross-sections to mark probable water-saturated zones and plan boreholes for their verification.
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Estimating Recharge Potential and Preferential Flow Paths in a Meander Close to a Recharge Pond Using ERT
Authors A. Casas, A. Sendrós, M. Himi, R. Lovera and I. CasadoThis study was launched to obtain more detailed understanding of the internal varieties of hydraulic conductivities within a meander located in the Cubeta de Sant Andreu aquifer that will be used for infiltration through a rechange pond. The spatial distribution of unsaturated hydraulic conductivity in the subsurface is of importance for hydrological modeling. Conventional methods to determine unsaturated hydraulic properties in the field are invasive and typically have a poor spatial resolution. In order to overcome these drawbacks, geophysical methods have received much attention in the last decades. The task required means to identify the architectural units affecting the groundwater flow, and to define the precise flow paths and residence times of the infiltrated water. The work was carried out by electrical resistivity tomography profiles that were used to create a detailed sedimentological model of the area.
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Geochemical and Geophysical Study of Beach Las Glorias, Guasave, Sinaloa, Mexico
We performed hydrogeochemical and geophysical study in the area Playa Las Glorias, Guasave, México. With Vertical Electrical Sounding (VES in modification ERT having high space resolution) we characterized the interface between slightly saline and saline water. Chemical analysis and granulometry supported conclusions about groundwater salinity along ERT profile and with depth.
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Investigating the Effect of NaCl Content of Pore Water on the Electrical Resistivity of Sand Samples in the Laboratory
Authors A. Hojat, S. Karimi Nasab and S. KosariGeophysical laboratory measurements are important to provide data base for better interpretation of field surveys as well as developing new applications of these methods. The purpose of this research is to study the effect of NaCl content of pore water on the electrical resistivity of saturated samples of sand. To do this, water samples of different salinities were first prepared and their resistivity values were determined. Then, laboratory measurements of electrical resistivity were carried out on saturated sand samples of different grading. The results of all the tests showed that as the salinity of the pore water is increased, the resistivity of the sand samples decreases. Moreover, it was observed that using samples of equal NaCl content, the coarser the soil, the higher resistivity is measured.
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Experimental and Theoretical Studies of the Temperature Dependence of Spectral Induced Polarization (SIP)
Authors K. Bairlein, M. Bücker, A. Hördt and S. NordsiekThe temperature dependence of spectral induced polarization (SIP) parameters is of interest for measurements near the surface where seasonal and meteorological temperature variations are present. Also measurements at greater depths, where the temperature increase with depth dominates, are influenced by the temperature. We analyze the temperature dependence by calculating the polarization parameters with an extended membrane polarization model, and by measuring the SIP-response of a limestone sample in a temperature range of 0°C to 60°C. Both simulations and measurements show a temperature dependence of the complex electrical conductivity. The phase shift slightly changes with temperature, depending on the pore geometry of the material.
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Marine ERT Modelling for the Detection of Fracture Zones
Authors P.I. Tsourlos, G.A. Tassis and J.S. RønningThe applicability of marine ERT surveys into the detection of underwater fracture zones is studied in this work. Various marine fracture zones models and measuring modes were tested using synthetic data which were subsequently subjected to inversion. In particular factors such as the effect of the sea water layer, the resistivity contrast, the overburden layer in both floating and submerged electrode modes are examined and compared. Among others, results indicate that the exact inclusion of the water layer into the inversion models is extremely important and that ERT surveys can be successful only for the first 10 meters of sea water.
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Detailed Study of Near Surface Resonance Properties Using Low Channel Microtremor Measurements - Physical Modelling Data
Authors Y.I. Kolesnikov, K.V. Fedin and A.F. EmanovThe method for detailed study of resonance properties of near-surface section using low channel microtremor measurements was tested on three-dimensional physical model with known characteristics. The model of layer overlying the vertical boundary of two mediums was investigated. It is shown that for measurements made with low-channel equipment and relocatable receivers the conversion of nonsimultaneous data to “common” time using synchronous data from fixed receiver can improve considerably the results of seismic microzonation. Experimental results are in good agreement with the data of finite element simulation.
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Magnetotelluric and Seismic Noise Techniques Combination for the Cerdanya Basin Characterization (Eastern Pyrenees)
Authors B. Benjumea, A. Macau, A. Gabàs, J. Ledo, P. Queralt and S. FiguerasA sedimentary Tertiary basin filled with unconsolidated sediments located in eastern Pyrenees has been subjected to a combine passive geophysical survey in order to increase knowledge of bedrock geometry and sediment properties. The methodology consists of combining and integrating both seismic noise techniques (H/V and array) and audio-magnetotelluric (AMT) and magnetotelluric (MT) data. AMT and MT data have been recorded along a NW-SE profile crossing the basin. Four 2D seismic noise arrays and 79 single station measurements were deployed at this profile. H/V technique has been suitable to obtain a soil fundamental frequency. Bedrock depth assessment can be obtained using S-wave velocity profiles derived from seismic noise array analysis. This information will allow establishing a soil fundamental frequency-bedrock depth relationship suitable for this basin. On the other hand, interpretation of the electrical resistivity model obtained from an AMT- MT survey will be constrained by the seismic results. This electrical resistivity model provides a detailed imaging of structural features such as the Cerdanya fault. This methodology, based on sediment characterization from shear-wave velocity and resistivity information, can be an attractive option for basin characterization essential for projects such as reservoir imaging.
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Application of the Controlled Source Radiomagnetotelluric Method in Remote Regions
Authors A.E. Simakov and A.K. SaraevThe new RMT-C system, based on measurements of the electromagnetic field of a grounded electric dipole as a controlled source, provided fulfillment soundings in remote regions, where is possible to measure only VLF radio transmitters signals by standard RMT instruments. Realization of CSRMT surveys using several main frequencies of the controlled source (CS) and their odd harmonics from the band 1-1000 kHz can provide short time of measurements at each sounding station. The distance from the source to measurements sites can reach several kilometers that can fulfill CSRMT measurements of wide areas using one CS installation. In receiving group ungrounded electric antennae can be used what is very important during measurements with bad conditions of groundings (on snow, ice, gravel, concrete etc.). Geoelectric sections obtained from 2D inversion results have good correlation with borehole data. The developed RMT-C system can be successfully applied in the near-surface geophysics for the solution of engineering and other tasks.
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Illuminating the Internal Structure of Two Monogenetic Volcanoes by ERT (La Garrotxa Volcanic Field, Spain)
Authors A. Casas, S. Barde-Cabusson, X. Bolós, D. Pedrazzi, R. Lovera, M. Himi, G. Serra and J. MartíEruptive activity of individual monogenetic volcanoes usually lasts few days or weeks. This short lifetime is not ever synonym of simplicity in terms of dynamics and structure. The construction of monogenetic cones is rarely witnessed from the beginning to the end and conditions for observing their internal structure are hardly reached. We provide high-resolution electric resistivity tomograms (10 m electrode spacing) of three monogenetic cones from north-eastern Spain. Details of their structure that could not be observed through other geophysical methods are revealed. We compare our results to geological observations, interpreting their underground continuation. With a maximum depth of exploration of about 100 m, we provide images of almost the entire edifices, highlighting the relationships between Strombolian and phreatomagmatic deposits in two multi-phases edifices. A main observation is a column of lower resistivity at the centre of the Puig d’Adri Strombolian cone, which we interpret as the eruptive conduit. This method provides information on the past volcanic dynamics of the monogenetic volcanic fields in general, which has real implications for the forecast of future activity.
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