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Near Surface Geoscience 2016 - 22nd European Meeting of Environmental and Engineering Geophysics
- Conference date: September 4-8, 2016
- Location: Barcelona, Spain
- Published: 04 September 2016
1 - 20 of 189 results
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Hydrogeophysical Survey of Groundwater Flow Pathways in an Alpine Headwater Basin
Authors C.W. Christensen, M. Hayashi and L.R. BentleyAlpine regions of the Canadian Rocky Mountains are important sources of freshwater for the semiarid Canadian Prairies. Yet, only recently have studies demonstrated that groundwater plays an important role in storage and subsequent release of snowmelt and rain. With limited case studies available in this region, a general understanding of groundwater flow processes in the alpine zone remains elusive.
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Groundwater Discharge along the Southern California Coast - Geophysical Images of Three States of Salt Water Intrusion
By J. JansenThe interface between fresh groundwater and saline water in coastal areas is frequently complex. The natural discharge of groundwater to the near shore zone is controlled by multiple factors including the permeability of the aquifer system, faults, confining units, and the hydraulic gradient in the aquifer. The natural balance is often disturbed by heavy pumping that can cause significant intrusion of salt water into the on-shore portion of the aquifer. The shape of the salt water wedge is affected by the pattern of pumping, the properties of the aquifer, and hydraulic boundaries like faults and confining units.
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Inversion of Frequency Domain Loop-loop Electromagnetic Data in 3D at Arbitrary Induction Numbers
Authors L. Cox, M. Endo and M. ZhdanovNear surface geophysics often uses man-portable electromagnetic instruments which can relatively quickly and inexpensively probe the earth for the 3D conductivity distribution.
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Evaluating Seasonal Variation of Groundwater Flow through an Alpine Meadow Using Passive Electrical Potential Measurements
Authors E.B. Voytek and K. SinghaAccurate quantification of groundwater flow patterns, both in magnitude and direction, is a necessary component of evaluating any hydrologic system.
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High-resolution Reflection Imaging for the Planning of a Double Train-track Tunnel in the City of Varberg, Sweden
Authors M. Dehghannejad, A. Malehmir, E. Lundberg, H. Möller and M. SvenssonA newly developed broadband MEMs-based seismic landstreamer system was employed for the planning of a double train-track tunnel in the city of Varberg, southwest Sweden. In addition to the refraction analysis and velocity tomographic modeling, reflection processing of the data was considered given the good quality of the data and realization of reflections in some raw shot gathers. Bedrock is strongly reflective in most cases and only at occasions when reaches near the surface it disappears in the reflection section. Bedrock undulation is clearly noticeable in most reflection sections and at one occasion it appears to be strongly diffractive. The diffraction signature is now known to be associated with a buried water tank used in fire emergency situations. Reflection seismic data greatly complements tomographic models and may support a deep bedrock at where the tunnel is planned to be excavated in the downtown Varberg.
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P- and S-wave Seismic Imaging of Overdeepened Alpine Valleys
Authors H. Buness, T. Burschil and G. GabrielOverdeepened valleys and basin can be found in glaciated regions worldwide. Due to their geological, ecological, and societal relevance they constitute a relevant geoscientific target. In preparation for an ICDP project (Drilling Overdeepened Alpine Valleys, DOVE), we carried out several reflection seismic surveys using high-resolution P-wave, horizontally pola¬ri¬zed SH-wave, and multi-component (SV- and SH-wave sources, 3-component re¬ceiver) techniques at a test site in the Tannwald basin north of Lake Constance. The first results of the P- and SH-wave reflection profiles are presented here. The seismic sections image well the internal valley structure of the Tannwald Basin; different facies are also distinguishable in the glacial sediments. The combined inter¬pretation of P-wave and SH-wave reflection seismics reveal more details than just one technique on its own by providing complementary information. P-wave seismics show a more coherent image with a higher penetration depth, while SH-wave seismics partly resolve more details due to their higher resolution. The combination promises to be an enhanced tool to investigate sedimentary successions in advance of scientific drilling.
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Surface-consistent Residual Statics Estimation with Genetic Algorithms - An Application to a Near-surface Seismic Survey
Authors M. Aleardi, E. Stucchi, A. Sajeva and B. GaluzziIn this work we apply a Genetic Algorithm (GA) approach to the residual statics computation problem. This type of geophysical optimization problem is characterised by many local minima produced by the so-called cycle-skipping phenomenon. The application of a global optimization method is particularly suitable in this context as it is able to jump out from local minima where gradient-based methods can easily be entrapped. We use an analytical objective function to test the capability of GA in finding the global minimum in case of highly non-linear multi-minima objective function. Because the residual statics optimization problem involves many unknown model parameters, in this analytical test we are particularly interested in analysing the rate of convergence (that is the number of evaluated models required to reach the global minimum) as the dimension of the model space increases. We then show the use of this methodology on a field seismic reflection data set acquired for near surface investigations. The application of the residual statics derived by the GA method produces final CMP gathers with flatter reflectors and a final stack section in which the continuity of the observed events increases.
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Rayleigh Waves Modelling Complexities in the Perspective of Full Waveform Inversion of Surface Waves - Synthetic Examples
Authors Z. Xing and A. MazzottiFull waveform inversion (FWI) has recently been considered for extracting detailed near surface information through the surface waves inversion. But the need of long computing time and the risk to get trapped into local minima make FWI cumbersome. Both these shortcomings are strongly dependent on forward modeling. In fact, forward modeling must yield very accurate seismograms and be computationally feasible. In this study we use an elastic finite difference modeling and discuss means to address, at least partially, these two conflicting requirements. In particular, we illustrate the possibility of attenuating the computing time problem by implementing the convolutional perfectly matched layers (CPML), and by performing the 3D to 2D correction on the observed data, thus allowing for using simple 2D forward modeling. It turns out that CPML has the ability to accelerate the computations compared with the standard tapering method, while maintaining the same efficiency in attenuating the unwanted artifacts from the model boundaries, and that 3D to 2D correction gives satisfactory results. Both of them result very useful in the perspective of surface waves FWI applications, also in view of the fact that other features, such as irregular topography, which cannot be neglected, require additional computing efforts.
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Towards 3D Inversions with Full System Modelling
Authors K.R. Andersen, E Auken and A.V. ChristiansenWe describe the setup for inversion of ground based TEM data using a 3D forward code and a full description of the measurement system. The response is calculated using a finite volume method where we solve for the electric field on the edges of a staggered grid and time step solutions using backward Euler steps. We convolve the calculated fields with the system response to compare with the measured data. In this way we include all system related effects in the calculation and this is important for the very early time signal. We describe how this is done for both forward and derivative calculations. For the forward calculation and the inversion we use an iterative solver. We show that the forward code is in good agreement with the analytic response from a half space.
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Determining the Depth of Gravity and SP Sources
Authors G.R.J. Cooper and R.C. WhiteheadCooper and Whitehead (2016) introduced a new method for determining the depth of magnetic sources that did not require a priori specification of the source type. This abstract shows that the method also works for various gravity and self-potential sources. References Cooper, G.R.J., and Whitehead, R.C., 2016. Determining the Distance to Magnetic Sources. Geophysics 81(2), p.J39-J48.
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Combined Land and River High-resolution Reflection Seismic Imaging of an Area Prone to Quick-clay Landslides in Sweden
Authors S. Salas-Romero, A. Malehmir and I. SnowballQuick-clay landslides are common in northern countries and the delineation of these materials is important when planning urban areas. High-resolution reflection seismic data were acquired on land along four profiles in an area prone to quick-clay landslides in southwest Sweden in 2013. These data complement previous investigations that show the influence of the underlying coarse-grained layers in the formation and thickness of the quick clays. The intercalation of the different glacial and postglacial sediments, and the structural information of the subsurface provide clues to the possible causes of a landslide. Apart from the land data, river seismic data, using one and six channels, were obtained. All the seismic sections show a clear undulating bedrock reflection, and signs of bedrock faults at shallower depth that maybe important in the generation of quick clays and landslides. The coarse-grained layer reflection is delineated on the land data, and several filled channels can be distinguished along the river. The presence of the coarse-grained layer indicates the possible large extension of the quick clays in the study area, which needs to be confirmed using geotechnical investigations.
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Detection and Analysis of Electromagnetic Radiation Emission from Macroscopic Fracturing of Cement-bound-granular Matter
Authors P.I.B. Ceralde and J.T. MaquilingCountries most prone to earthquake damage have been in search of a possible earthquake precursor. This thesis aims to detect and measure the magnetic field component of the Electromagnetic Radiation (EMR) emitted by quasi-brittle materials that undergo macroscopic fracturing. Cement-Bound Granular Material (CBGM) beam composites were prepared by mixing cement, sand and gravel. Fine sawdust was added to form another aggregate component of the CBGM variant. Impact loading was repeatedly performed on the beams to induce fracture until failure. Six Vernier software magnetic field sensors, with sensitivity range of ±6.4x10-3 T and 0.0002 mT precision, were strategically positioned around the beams to detect the magnetic field (MF) component of the EMR emission. Initial calibration was done to minimize noise in the laboratory. The time of impact was determined in the form of collision noise using a sound level meter at fast time setting. CBGM beams consisting of cement, sand and gravel produced magnetic field emissions measuring from 0.58-1.07 μT while the CBGM beams with dispersed fine sawdust emitted 0.55-1.28 μT. Increasing the input energy from the mass of weight drop by 150% resulted to a 10% increase on the mean value measurements of magnetic field emission magnitude.
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The Holocene Tordera Delta System - On/Offshore Sedimentary Sequences and Evolution
More LessThe Tordera River delta system is located on the NE coast of the Iberian Peninsula. It is a coarse-sand delta originated from the erosion of the granitoids in the Catalan Litoral mountain range system. The Tordera delta has originated in a Mediterranean fluvial regime and with the influence of coastal drift currents from the SW. The sediments carried by the Tordera, together with the contributions from local streams has originated the different sand bodies present in the Blanes inner shelf. From new marine seismic data we have described the internal structure of these sand bodies as well as defined three seismic sequences which are Ph, Sd2 and Sd3. At the same time, the seismic profiles have provided additional support to the correlation of these sequences with the sedimentary deltaic sequences, as well as detail to the evolution of these sand bodies during the last sea level rise. The samples obtained though vibrocores and dredges have allowed the sedimentary characterisation of the sand bodies and their correlation to the deltaic sequences (absolute and relative aging) as well as the absence of sedimentary drift transport from the NE.
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On the Characterization of a Geophysical Diagnostics Resolution Index within the Seismic Damage Scenario Construction
Authors A. Teramo, D. De Domenico, D. Termini, M. Romeo, C. Teramo, N. Morey and C. SaccàA methodological approach for selecting areas to be subjected to geophysical diagnostic is proposed to determine the damage susceptibility of territory elements within the construction of a seismic damage scenario for the city of Messina. The morphology of the urban context have made difficult the programming and execution of those geophysical surveys more consistent with the objective to be achieved. On the basis of different indicator typologies, an empirical relationship has been established to identify the territory elements of a higher significance where to focus a greater diagnostic commitment for the acquisition of specific data to be used for seismic vulnerability assessments at a large scale. To this end it was defined a diagnostic resolution index, related to the specific characteristics of the territorial system, stands out as a significant interest element in the study and evaluation of the regional multi-hazard conditions (shallow water-table, presence of debris of buildings referable to the past earthquakes, high level of heterogeneity of the lithotypes, the widespread presence of surface faults, ...) The analysis of preliminary results have made possible the assessment of the reliability of the proposed procedure in order to properly planning a diagnostic campaign related to the safety reducers of the area in study.
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TDR Measurements of Magnetic Characteristics of Materials
By R. PersicoIn this contribution, the possibility of measuring possible magnetic properties of materials by means of a TDR probe is studied. A transmission line model is adopted and data in time and frequency domain are exploited together. Simulation results are shown, at the moment based on a bifilar line model.
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Time Domain IP Profile by Multi-current Transmission Technique - Water Tank Experiment and SP Noise Effect Estimation
Authors Y. Yamashita and F. LebertWe conducted time domain chargeability measurement by multi-current transmission technique using a water tank and mineral ore which has certain IP effect in the purpose of verifying the method to calculate chargeability from the data acquired by multi-current transmission measurement using Code Division Multiple Access (CDMA) technique . We also evaluate the effect to chargeability calculation of SP noise thorough numerical experiment. We confirmed that time domain chargeability measurement is available through the experiment using water tank and mineral ore. We also evaluated the effect of SP noise to time-domain chargeability measurement by numerical experiment. The precise current control and appropriate SP management are important for reliable chargeability measurement with multi-current transmission measurement.
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Enhanced Characterisation of Radiologically Contaminated Sediments at Sellafield by MSCL Core Logging and X-ray Imaging
Authors O. Kuras, J. Shreeve, N. Smith, J. Graham and N. AthertonVisual observations and electrical geophysics alone showed limited ability to characterise a complex Quaternary sequence of glacial sediments at the Sellafield site with sufficient spatial detail, and conventional high-resolution logging was impracticable. By applying non-destructive high resolution MSCL and X-ray core logging we have parametrically characterised and imaged the stratigraphy in detail for the first time. This approach has allowed us to identify geological units with increased confidence, and link these units to a depositional process. The results open up the opportunity to link geological observations at Sellafield with regional type localities and the regional stratigraphy. The approach holds promise for applications where conventional high-resolution borehole logging is not possible, or not able to fully characterise the geology.
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2D Modeling of Controlled Source Radiomagnetotelluric Data Observed on Buried Faults Close to St. Petersburg/Russia
Authors B. Tezkan, I. Muttaqien and A. SaraevControlled source radiomagnetotellurics (CSRMT) is a new and innovative method of near surface geophysics. We applied this method for the detection of a buried fault beneath a test area close to St. Petersburg. During this survey, a rectangular current was injected into the ground using an electrical horizontal dipole with a length of 700 m and O.5, 11.5, 30 and 105 kHz – as well as their subharmonics - were used as main frequencies. The time series of two horizontal field components and three magnetic field components were observed at 97 stations with a station interval of 20 m in the near, the transition, and the far field zone of the electrical dipole. Transfer functions were derived in the frequency interval of 1 kHz to 1000 kHz from the observed electric and magnetic time series using the newly developed processing software. They showed a smooth dependence of frequency indicating the reliability of the observed CSRMT data. The CSRMT data were interpreted in the far field zone by using a 2D inversion algorithm and in the near zone by using 2D forward calculations. The derived 2D conductivity models showed clearly the location of buried faults as large resistivity contrasts.
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On One of Precise Solutions to Integrate Hydrocarbon Mobilization Rhythms, Dense Reservoir Development Stages and Sand Recovery Geological Evolution
Authors V.I. Popkov, A.M. Shterenberg, V.V. Gusev and Е.V. MitinaIt is quite possible to achieve the growth in efficiency of geo-exploration works through the increase in drilling operations and this is the strategy of permanent technology. The improved technology strategy supposes the growth of rate of success in each well and constant amount of drilling operations. The costs for technology improvement are significantly lower than exponentially increasing costs for well pad drilling. The authors present the systematic evolution/topological theory of global solution for Cis-Ural region hydrocarbon mobilization as subduction and generalized saturation of the middle chain of the Urals, deformation of tunneling, plastic decompaction of fracture porous geo-media. Migration deformation provides great effect upon the structure of fractured permeability in aqueous matrix, energy with sand recovery, ecology and economics. The paper presents analytical solution of Darcy-Fick’s energy law for secondary deformation moments, plastic saturation of miming concentrations and formation of oil and ore material fields. The authors substatiate the systematic methodology in search, exploration and development of decompacted reservoirs with classtic and unconventional traps. They also present lithological/facies rhythms of migration glimmering foamy structure, geological risks in drilling. The authors note unconformity of initial lithological stratification cycles and rhythms of secondary processes in neo-hydrodynamics and evolutionary sand production.
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Remediation Investigation of a Failing Retaining Wall Structure
Authors A.J. Verweerd, S. Williams and P. ArnoldThis presentation is a case study combining geophysical & geotechnical investigation as well as structural deformation monitoring of a failing drystone retaining wall structure in the United Kingdom. Data collected and interpreted during this project was used to design a remediation solution, stabilizing the structure while retaining the wall's original appearance. The approach chosen in this study includes seismics, ERT and GPR studies combined with a targeted intrusive campaign to limit further destabilization of the structure. The geophysical surveys were executed close to the retaining wall, on the highroad above the wall as well as on the wall face itself. Both data sets were combined into a geotechnical interpretation which formed the basis of the remediation solution. In addition to the geophysical and geotechnical investigation a remote structural monitoring system was deployed to monitor the behaviour of the structure, ensuring the safety of the general public and infrastructure.
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