- Home
- Conferences
- Conference Proceedings
- Conferences
25th European Meeting of Environmental and Engineering Geophysics
- Conference date: September 8-12, 2019
- Location: The Hague, Netherlands
- Published: 08 September 2019
61 - 80 of 141 results
-
-
Combined GPR and ERT Survey at the Marathon (Plasi) Archaeological Excavation Site
Authors J.D. Alexopoulos, N. Voulgaris, S. Dilalos, N. Souglakos, G.S. Mitsika and Y. PapadatosSummaryThe excavation trenches by the Department of History and Archaeology of the NKUA at the archaeological site of Plasi Marathon (Attica, Greece) have already revealed several architectural remains of the Classical period. A combined GPR and ERT survey was initiated in order to determine the existence and geometry of additional buried structures in the unexcavated parts of the site. The results of this geophysical survey will not only assist the archaeologist's planning for the next excavation steps, but will also provide valuable information for the density of habitation in the area, a significant factor for the understanding of the importance of ancient Marathon. Fifty-two GPR and eighteen ERT profiles were carried out in a selected area. After data processing, the obtained radargrams and resistivity tomograms are presented in the form of fence diagrams. Moreover, volume/depth slices have been extracted for specified depths from GPR and ERT in order to compare their results. Several identified geophysical anomalies can be interpreted as archaeological domestic remains, supporting a rather dense pattern of habitation, hence the archaeological significance of the site.
-
-
-
High Resolution Electrical Resistivity Tomography Imaging of a Coastal Mine Tailings Deposit, Portman Bay, SE Spain
Authors A. Urruela, M. Canals, L. Rivero, M. Himi, A. Casas, R. Lovera, R. García, A. Sendrós, J. Frigola and D. AmblàsSummaryThe Portman bay (SE of Spain) was infilled with mineral tailing for 33 years by the mine industry that operated in the area. What was a clean crescent-shaped bay in the year 1957 had disappeared by 1990 under 60 Mt of dumped waste. In this study we propose the use of electrical resistivity tomography (ERT) for the characterization of the mineral tailings that infilled the bay.
Two field data acquisitions were performed obtaining regional and detailed ERT data. The combination of this acquired data with boreholes and historical aerial photography has allowed to generate a 3D integrated model of the mineral tailing infill. This detailed model suggests a 44% increment of the volume of the infill from previous studies. Furthermore, a dense ERT grid was acquired and yielded a meter-scale resolution model of the internal heterogeneities.
-
-
-
Near Surface Seismic Reflection Survey - A Comparison of P- and S-waves Vibratory Seismic Sources
Authors F. Gallais, K. Becker, M. Le Feuvre, M. Verdurme and P. CôteSummaryThis paper describes the results of five seismic reflection surveys planned to evaluate the capacity of different vibratory sources to image a target interface in 40 m depth. Between 2015 and 2017, we acquired a 48-channels seismic profile that serves as a reference. During the different phases of acquisition, we used a sledgehammer and four different light vibratory sources, able to emit P- and/or -S-waves. Then, we compared the performance of the sources used in term of resolution, S/N ratio, optimum stacking number and repeatability. One of the vibratory source and the sledgehammer in S-wave mode show good performance and are particularly successful sources to give high-resolution seismic profile of the near surface.
-
-
-
Seismic Imaging of the First 30-Meter Weathered Layer in a Karst Environment (H+, Poitiers)
Authors M. Dangeard and J.L. MariSummaryNear-surface seismic methods are mainly used to determine the geometrical characteristics of the hydrosystems. Recent methodological advances suggest the high potential of these methods to investigate the mechanical properties subsurface by exploiting the full wealth of seismic records. Indeed, with vertical component seismic data recorded we can extract: (i) P-wave first arrival times to provide P-wave velocity section; (ii) surface-wave dispersion to estimate local 1D VS model, and (iii) a reflectivity section starting from the surface. All this information can be combined in order to better characterize the subsurface providing hybrid seismic sections.
-
-
-
Effects of Physical and Acquisition Parameters on Fundamental Dispersion Curve in MASW Method
Authors H. Karsli and M. ŞenkayaSummaryIn this study, the effect of physical and acquisition parameters on the continuity and resolution of fundamental dispersion curve (frequency-phase velocity) has been examined by modeling the synthetic seismograms in Multichannel Analysis of Surface Waves (MASW). The influences of decreasing S-wave velocity or increase in the thickness of the layer on the dispersion curve are observed rapidly as drop in lower frequency zone, while the effect of the increase in the velocity or decreasing of the thickness caused fundamental dispersion curve to shift to higher modes. For the effects of acquisition parameters (offset-XO, geophone interval-dx, number of geophones-N, spread length-L=(N-1)*dx), the fundamental dispersion curve was re-picked from seismograms synthetically modeled by using the simple harmonic summing technique. The tests show that the largest spreading length and offset must be used to obtain the dispersion curve in a widest frequency range and high quality. However, geophone interval for larger spreading should be selected by without wavenumber aliasing. Therefore, synthetic tests showed that if one wants to obtain continuity and resolution of fundamental dispersion curve when analyzing of field data, acquisition parameters may be selected as 1m≤dx≤2m, X0≥Zmax or X0=L for N<24 and 0.5m≤dx≤2m, X0≥L/5 or at least X0 4*dx.
-
-
-
A Comparison of Multiple Attenuation Strategies for Shallow Water Ultra-High-Resolution (UHR) Seismic Reflection Data
More LessSummaryThe processing and interpretation of Ultra High Resolution (UHR, > 2k Hz) marine seismic data can be very challenging, especially in shallow waters (< 50m depth), where multiple reflections can overprint primaries in areas of interest, potentially creating ambiguities in the interpretation. In this paper, we compared the performance of five different multiple attenuation techniques (τ-p deconvolution, f-k demultiple, Radon demultiple, Surface Related Multiple Elimination (SRME), and τ-p deconv + SRME) on a very-shallow water (<15m depth) multichannel UHR seismic dataset. In this case, techniques independent of the moveout differences between primaries and multiples (τ-p deconvolution and SRME) attenuated multiples effectively, producing minor changes on primaries and without significant addition of noise. In contrast, f-k demultiple, Radon demultiple and the combined application of τ-p deconvolution and SRME were inefficient at removing multiples. SRME was identified as the most efficient technique and allowed for a significant improvement in the interpretability of the final seismic image.
-
-
-
Wave-Equation Datuming Applied to Very High-Resolution Deep-Towed Multichannel Seismic Data
Authors F. Colin, S. Ker and B. MarssetSummaryUnderstanding geohazards in great water depths requires the use of remotely deployed technologies in order to obtain the vertical and lateral resolutions required to model the medium. Deep-towed multichannel seismic is a powerful tool that can provide such resolutions, however data it produces requires careful, dedicated, processing. During acquisition of deep-towed seismic data, the vertical movements of the tow-fish cause vertical changes in the 120 m long streamer's shape. These variations have to be calculated to recover the acquisition geometry. This was solved by using travel times to invert for key parameters of the streamer's shape. Furthermore, unlike conventional surface-towed seismic, the sources and the receivers do not share the same depth datum which prevents the application of most conventional marine seismic processing algorithms. Wave-equation datuming (WED) is a method that allows moving the positions of sources and receivers to a common depth datum. This contribution presents how the WED method has been adapted to the characteristics of deep-towed multichannel seismic acquisitions. The application of this processing step to deep-towed seismic data allows the application of “conventional” algorithms, such as a NMO-stack-migration approach, thus facilitating the processing sequence of these unconventional seismic data.
-
-
-
Rock Masses Characterisation Using High Frequency Piezoelectric Systems
Authors A. Butcher, A. Ridsdale and J. KendallSummarySeismic methods provide important in-situ measurements of the rock mass strength, which can be assessed through variations in seismic velocities. The frequency range in which seismic instruments operate dictates numerous key elements of a survey (e.g.detectability limits and resolution), and for engineering applications it is often advantageous to operate in kHz frequency range.
Piezoelectric sensors are rarely deployed in seismic surveys, but offer the potential for higher frequency content and more repeatable measurements compared with conventional instruments. This results in increased spatial resolution, and improvements in the stability of spectral measurements (e.g., spectral ratio methods).
To better understand some of the main characteristics of the piezoelectric system, we carry out a series of laboratory measurements on a range of different lithologies. Measurements were made to initially determine the frequency content on the system, followed by the response of the rock samples to these high frequency signal. We then present two crosshole datasets from ground excavations at Hinkley Point C, acquired using a piezoelectric seismic system and a conventional sparker system.
-
-
-
Global Inversion of Pressure Dependent Acoustic Velocity Data Based on a New Double Relaxation Model
Authors J. Somogyine Molnar, T.E. Dobroka, T. Ormos and M. DobrokaSummaryIn this paper with the further development of our previously published single relaxation model (SRM), a new petrophysical model (the double relaxation model - DRM) describing the hysteretic pressure dependence of acoustic P wave velocity is presented. Since it is likely that several relaxation mechanism occur in the rock at the same time, the new model considers two or more physical mechanisms (e.g. the closure of pore volume or microcracks or friction on grain boundaries etc.) responsible for the pressure dependence of propagation velocity. Using the model equation as forward modeling formula, a global optimization algorithm (Simulated Annealing) was applied to solve the inversion problem and to determine the petrophysical parameters of the model. Inversion results proved that the calculated data matched accurately with measured data, so the new model was tested with success on laboratory measured data. On the other hand one can see that the new DRM model resulted in a more accurate fit compared to the SRM model.
-
-
-
Landslide Investigation and Monitoring Using Self-Potential Methods
Authors C. Sujitapan, M. Kendall, J.S. Whiteley, J.E. Chambers and S. UhlemannSummaryLandslides are complex and heterogeneous phenomena involving properties of the subsurface. To study landslide processes, we use the self-potential (SP) method to investigate physical characteristics of the subsurface and monitor the accumulation and movement of groundwater associated with reactivated landslides at Hollin Hill, UK. The SP measurements consist of SP mapping in 2D and monitoring SP profiling. Six SP mappings are acquired in different climatic conditions. They show positive charges carried in the direction of the fluid flow, producing positive anomalies on the surface located at water discharge area and negative anomalies on infiltration area. The anomaly pattern reveals strong relationship between landslide morphology and flow regions particularly in the back scarp and secondary scarp. Moreover, the mappings are compared to precipitation data. They show the significant seasonal variations that SP signature possibly links to rainfall. However, it is still a bit unclear. Consequently, an analysis of the continuous SP monitoring are applied for high temporal resolution. The monitoring result shows that most of SP variations with time are linked to rainfall events and soil moisture contents. Consequently, the SP could be a possible method to monitor groundwater conditions and provides precursory information as an early warning of landslides.
-
-
-
Detection of Capacitive Couplings in Ground-Based TEM Data with a 1D Convolutional Neural Network
Authors T. Frederiksen and J.J. LarsenSummaryTransient electromagnetics (TEM) is a well-established method for imaging of sub-surface resistivity structures. The method is often used from a moving platform providing densely sampled measurements of the sub-surface structures in 2D or 3D. When measurements are performed close to man-made conductors e.g. buried cables and pipes, the data will be contaminated by coupling artefacts, which must be culled from data sets prior to inversion. This can be a labor-intensive task for large data sets and several methods for automation of this process has been investigated. Here we explore the use of a convolutional neural network (CNN) for detection of couplings in data from a towed, ground-based TEM system. The CNN consists of two 1D convolutional layers followed by three fully connected layers. The proposed method is evaluated by comparing with a neural network based approach that have previously been used to detect couplings in airborne TEM data and is found to have better performance. The performance is presently limited by the size of the training data set.
-
-
-
Airborne Electromagnetic and Radiometric Peat Mapping A Case Study from a Bog in Germany
Authors B. Siemon, M. Ibs-von Seht and S. FrankSummaryKnowledge on peat volumes of peatlands is essential to estimate carbon stocks accurately and to facilitate appropriate peatland management. This case study uses helicopter-borne electromagnetic and radiometric data to investigate a bog in Germany. Airborne methods provide an alternative to ground-based methods, which are labour intensive and unfeasible to capture large-scale spatial information.
One of the airborne surveys BGR conducted at the North Sea coast over the past two decades covers the Ahlen-Falkenberger Moor, an Atlantic peat bog (39 km2) investigated by the Geological Survey of Lower Saxony. This enables comparison of airborne and borehole results.
The lateral extent of the bog is derived from low radiometric and elevated surface data. The vertical extent results from smooth resistivity models in combination with a steepest gradient approach as well as from radiometric data. The latter requirs scaling of the relative depth values. Depths derived from electromagnetic data are usable for this scaling due to their similarity to borehole peat depths. The mean difference of the combination of electromagnetic and radiometric depths and the peat depths of about 100 boreholes is very small (-0.08 ± 1.09 m), but may differ significantly (>±2 m) at some points.
-
-
-
Long Term Variation of Geomagnetic Curvature Recorded by Absolute Measurement in Different INTERMAGNET Observatories (Comprehensive Study)
By A. CsontosSummaryThe main task of the present day geomagnetic observatories is to record the elements of the geomagnetic field. This task is performed if the intensity and the direction of the geomagnetic field became known on one point. Standard observatory instrumentation gives further chances to measure the magnetic gradients and identify several changes of the magnetic gradient. These methods were tested before. In this paper we present the comprehensive study of three INTERMAGNET observatory’s long term dataset. In the focus of our data processing is the variation of a special magnetic gradient which is always observed during routine absolute magnetic measurements. As a cosequence we will study only the inclination readings of the complete set of absolute measurement. The difference between the two absolute values of inclination records will represents the curvature of the geomagnetic field measured in the magnetic meridian plane.
Long term high quality observatory dataset can provide a good basement to study the fluctuations when the observation is far away from strong conductivity anomalies.
It will be shown that we can find quiet periods when the studied difference shows high stability. On the other hand the disturbed periods also appear in every observatories.
-
-
-
Analysis of Influence of the Data-Selection Procedure on 3-D MT Inversion Using Gyeongju Data in Korea
More LessSummary3-D MT inversion has been widely used to describe deep subsurface structures, but MT data are prone to be contaminated with noise. Although some pre-processing is done before inversion, the quality of some data can still be poor. To prevent noisy data from degrading inversion results, we may exclude noisy data in the inversion process. In this case, we need to consider the trade-off between the quality and quantity of data. We investigate the influence of the data-selection procedure on inversion results using AMT data acquired in Gyeongju, South Korea. Our inversion results show that the balance between the quality and quantity of data is important to obtain reasonable inversion results.
-
-
-
On a New Method of Detecting Layer Boundaries at the Borehole Measurements by Gamma Logging
Authors S. Kataev, S. Kataeva and A. MillerSummaryA method for solving the problem of determining the boundaries of layers from logging measurements by gamma-ray logging, based on the method developed earlier by the authors to find the parameters of the incoming flow of events from observations of the moments of occurrence of flow events. The effectiveness of the method is demonstrated on the model laboratory experiment and on the real data. The applied algorithm allows to determine the initial option of splitting into layers in automatic mode. Clarification of the boundary layers is implemented by the interpreter in interactive mode
-
-
-
Development of 3D Inversion Algorithm for Time-Domain Airborne Electromagnetic Data
Authors S. Jeong, M. Yi, A. Johmori and Y. SasakiSummaryRecently, airborne time-domain electromagnetic (ATEM) methods are gaining popularity for applications in mining, geotechnical, and environmental problems due to their efficiency in covering vast areas. To interpret ATEM data, 1D methods are commonly used because of their efficiency in handling large scale data. However, 1D methods yield an erroneous resistivity model when their basic assumptions are violated. In this study, we developed 3D inversion algorithm for ATEM data which is based on inverse Fourier transformation of frequency-domain responses and sensitivity. To efficient calculation of the multisource response and sensitivity, an edge-based finite element method with the direct solver is adopted. In addition, to reduce time for calculating sensitivity, a moving footprint approach was also used. In numerical experiment with simple 3D model containing conductive targets, subsurface model was successfully reconstructed.
-
-
-
Saltwater Intrusion Monitoring with the SAMOS System as a Basis for Groundwater Management of Coastal Aquifers
Authors M. Ronczka, T. Günther, M. Grinat and H. WiederholdSummarySaltwater intrusions are a major problem for the freshwater supply in coastal regions. The project go-CAM is part of a research initiative to develop a platform for groundwater quality assessments. The main objective of the presented study is the monitoring of the freshwater/saltwater interface with the vertical electrode chain SAMOS in the vicinity of the North Sea. The first system was installed in December 2018 near Jever in the Sandelermöns region, where ongoing chloride monitoring detected an increasing chloride concentration at 50 m depth. ERT and HEM surveys provide an overview about the resistivity distribution in the investigated region and are used to find other SAMOS locations. The data are influenced by the drilling process indicating that the equilibrium is still not reached after four months of monitoring. An inversion procedure separates drilling effects from undisturbed conditions. First results show that the transition zone towards saline groundwater starts at approximately 40 m depth and reaches a minimum resistivity of 25 fim at 50 m depth.
-
-
-
Incorporating Petrophysical Variability to Coupled Hydrogeophysical Modelling of DC Resistivity in Heterogeneous Coastal Aquifers
Authors A. Gonzalez Quiros and J. ComteSummaryGeophysical techniques are well suited to provide additional data for the parametrization of groundwater models. Joint use of geophysical and hydrological information through coupled modelling and inversion relies in an appropriate transfer function, the petrophysical model. Due to uncertainties in the spatial distribution of petrophysical model parameters, constant distributions are often used as a simplifying assumption, even when heterogeneity is present in the subsurface. When using this simplification, discrepancies can arise in the computed geophysical response. In this work, we show how spatially variable properties and simultaneous petrophysical models can be utilized in a coupled hydrogeophysical modelling. The developed coupled modelling relies in the definition of adequate transfer functions between models (hydrological and geophysical), providing direct correspondence between the spatial distribution of the hydrogeological and electrical properties. It has been observed that the effects of lithological heterogeneity can have as much importance as fluid salinity variations only. Therefore, when assuming constant petrophysical parameterizations geophysical results might be interpreted incorrectly. The understanding of these effects is a necessary step for a correct application of the petrophysical model in hydrogeophysical studies and shows the importance of petrophysical parameter variability when using coupled modelling methodologies for accurate imaging and quantification of saltwater intrusion.
-
-
-
Investigating the Saturation State of Higher Strength Rock (HSR) by Geoelectrical Imaging at the Core Scale
Authors O. Kuras, T. Debouny, P. Wilkinson, L. Field, A. Milodowski, R. Metcalfe and S. NorrisSummaryThis study demonstrates how the capacitive resistivity imaging (CRI) technique can be used at the laboratory scale to derive a spatially resolved 3D model of water content in a core sample of Higher Strength Rock (HSR). Understanding groundwater flow and the transport and retardation of any radionuclides in fractured HSR is a key research aim associated with the geological disposal of radioactive waste. Retardation and incorporation of radionuclides from groundwater into the surrounding rock mass is important for the safety case for a geological disposal facility (GDF) in HSR. For a rock with dual porosity, such retardation and incorporation may be enhanced if the radionuclides are able to diffuse from fractures that support advection into effectively stagnant porewater within the rock matrix. This diffusion is termed Rock Matrix Diffusion (RMD). Improved non-destructive estimation and spatial mapping of water content in HSR under “fresh rock” conditions may offer new insights in RMD research.
-
-
-
Visualising Groundwater Flow Using Time-Lapse Electrical Resistivity Tomography
Authors M. Karaoulis, W. Bakx, P. Doornenbal, P. Kruiver and S. RijpkemaSummaryWe performed Electrical Resistivity Tomography (ERT) measurements around a groundwater extraction well in a field of drinking water extraction wells. Oxygen enriched water is injected in a well during short periods as a purification step to remove iron from the groundwater. The goal of the pilot is testing the performance of ERT as a monitoring tool. Cross-hole ERT measurements were performed in a time-lapse mode to link changes in resistivity to groundwater flow expressed by variations in temperature and possibly oxygen content from the treatment. We show one example of the change in resistivity over a period of 16 hours. The changes in resistivity are small, in the order of 0.5 %, but proven to be above the noise level. When the time-lapse results are visualized in a movie (instead of just one snapshot), the patterns of change are consistent and can be linked to groundwater flow. We conclude that the ERT methods is suitable to be used as a monitoring method for groundwater flow. An additional future dataset will consist of temperature measurements using fibre optics Active Distributed Temperature Sensing. The next step will be to use the information from both methods to optimize well operation.
-