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23rd European Meeting of Environmental and Engineering Geophysics
- Conference date: September 3-7, 2017
- Location: Malmö, Sweden
- Published: 03 September 2017
141 - 157 of 157 results
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3D Modeling and Bedrock Determination Using Electrical Resistivity Inversion
Authors A. Najafabadipour and G.R. KamaliSummaryElectrical tomography method is an optimized network acquisition method which uses appropriate array to detect subsurface targets. Acquired data gathered from acquisition through the application of various methods of optimization such Gaussian- Newton, Semi-Newton are used for modeling and interpretations. Tikhonov regularization terms have been used here to minimize the objective function. In this study, the bedrock has been selected for modeling the electrical tomography as it had special and sufficient resistivity contrast with the surrounding environment. Acquisitions were gathered using Schlumberger array in an orderly network. For the inversion of the data, IPI2WIN software was used and for 3D modeling VOXLER software was applied. Results showed that the bedrock was recognized for its high electrical resistivity against its surrounding area. The relative particle condition and the existence of clay can also be estimated in the obtained levels qualitatively.
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Seismostratigraphic Modeling Using Constrained HVSR Data
Authors R. Martorana, M. Agate, P. Capizzi, F. Cavera and A. D’AlessandroSummaryAn application of HVSR inversion is presented in order to verify the effectiveness of this technique for purposes of reconstruction of the buried geological setting where stratigraphic constraints are available. Specifically, the reconstruction of the stratigraphy in the studied area has been obtained by a seismic-stratigraphic three-dimensional modeling. This allowed for geophysical and geognostic data derived from surveys carried out during this study, as well as previously by the municipality of Palermo.
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An MASW Survey for Landslide Risk Assessment in Novi Seher, Bosnia and Herzegovina - A Case History
Authors K. Suto, M. Urosevic and S. KomatinaSummaryA heavy rainfall caused an extensive damage in the catchment area of River Sava in May 2014. In response, the Association of Geoscientists and Environmentalists of Serbia organized a Geoscientists without Borders project for 2015–2016 to assess landslide potential at six locations of Serbia and Bosnia and Herzegovina. Geophysicists from many parts of the world, local students, local government staff and local residents participated in the surveys carried out in three phases. Among these surveys, this paper presents one in Novi Seher in Bosnia and Herzegovina. The data were primarily collected for reflection survey and the MASW processing used a subset of the data by extracting appropriate traces. The analysis resulted in S-wave velocity sections which are geologically plausible, with a potential slip surface between 0 and 10m deep. This result will be integrated with seismic reflection and refraction analyses to contribute to designing disaster mitigation plan.
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Morphometric Analysis for Landslide Susceptibility in Sukasari and Surrounding Area, Tanjungsari, West Java, Indonesia
Authors M.L. Dwiyoga, M.F. Mawaridi and M.A.J. AnandiSummaryThe general prevalence of landslides and mass wasting in West Java region shows interrelation to heavy weathering and slope condition. Alerting issue of geological hazard should be considered and inspected thoroughly by the researchers because of the danger it holds with human lives and infrastructure losses. This research was conducted in the administrative area of Sukarasa and the surrounding vicinity, Tanjungsari District, Bogor Regency, West Java, Indonesia. Three methods were used in the research, i.e; (1) Geological map and slope steepness, (2) Morphometry analysis, (3) GIS data using LiDAR satellite images. Area consisted of lithological properties, i.e; (1) Claystone, (2) Volcanic intrusion. Morphometry analysis includes the supporting aspects such as; morphography or morphogenetic that later will be applied for quantitative evaluation in landform. It also gives direct separation in dividing the research area with two classes of weathering and erosion, i.e; high, medium, and low level. Integrating the results with each method rendered, should give insight into final outcome in mapping landslide potential. Therefore, based on Landslide Risk Potential Map, it can be concluded as a percentage which resides of high risk by 60%, 30% medium risk, and 10% low risk of the total area of the research.
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Applying Bat Metaheuristic Algorithm for Building Shear Wave Velocity Models from Surface Wave Dispersion Curves
More LessSummarySurface wave dispersion analysis is a suitable tool for near-surface seismic characterization; however, the main problem arises from the non-unique nature of the dispersion curve inversion. For inversion of surface wave datasets different nonlinear inversion algorithms are proposed. These algorithms efficiency were proved by different case studies. Recently, the bat algorithm (BA) as a nature-inspired algorithm is introduced for optimization problems in engineering. The bat algorithm is a very promising alternative for inversion of dispersion curve. In this study, capability of the bat algorithm investigated to estimate of Vs profile. First the bat algorithm was written and processed in Matlab and then the efficiency of the algorithm evaluated by inversion of broadband synthetic dispersion curves from a simple model. Also for more investigation the ability of proposed algorithm, the search space extended and also noise was added to synthetic data. Moreover finally a limited frequency (2–8Hz) synthetic dataset was inverted. Results demonstrated that the bat algorithm is a new metaheuristic technique in analysis of surface wave data.
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Addressing the Non-linearity of Full-waveform Inversion with a Probabilistic Approach
Authors J. Hunziker, E. Laloy and N. LindeSummaryDeterministic full-waveform inversion will converge towards a local minimum if the forward-simulated data based on the starting model differ from the observed data by more than half a wavelength. In order to include prior information and derive posterior probability density functions that are independent of the starting model, we use a global sampling method. We consider a synthetic multi-Gaussian test case and use an efficient adaptive Markov chain Monte Carlo (MCMC) method in combination with dimensionality reduction through circulant embedding to invert the noise-contaminated data. By considering multiple MCMC runs with different starting models, we find that we always recover model realizations with appropriate data misfits, but that different runs lead to different estimated posterior distributions. This is a consequence of the severe non-linearity of the full-waveform inversion problem and the finite length of our MCMC chains. Nevertheless, the different runs give a good idea of the types of subsurface models that are consistent with the data.
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Imaging Aji Chai Salt Dome through 3D Binary Inversion
Authors S.Y. Sayyadi and H.V. Vali GhazviniSummaryIn order to avoide facing problems of both methods, we used binary formulate. In this way, we are able to use advantages of both methods for gaining our goal. We limited the density contrast distribution into two value which is zero or a constant value. Finally, by using Tikhonov regularization, the inverse problem was formulated for imaging salt body. For clarifying the accuracy of this method, we used it for synthetic data and real data. Our studying region was a salt body which is located in south of Miane, east Azarbaijan Province at center zone of Iran.
These results show that our inversion method is a good way for interpreting the gravity data for imaging salt bodies.
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2D Joint Inversion of MT and Full-waveform Seismic Data
More LessSummaryRecently, the interest in joint inversion of different geophysical data has been significantly increased. Not only the model constraint but also the constraint between different physical parameters should be taken into consideration in the inversion. Using a four-point difference cross-gradient constraint, a 2D joint inversion algorithm of MT and full-waveform seismic data has been developed. The synthetic experiments show promising results. The joint inversion is more valid than the separate inversion, significantly improving the accuracy of resistivity image and somewhat promoting the quality of velocity image.
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Numerical Investigation on DC Resistivity Anisotropy Modelling and Imaging for Near-surface Structures
More LessSummaryThe present DC electric resistivity tomography cannot incorporate anisotropic media. The research on the resistivity anisotropy modelling and imaging is rather sparse. So, this study focuses on the resistivity anisotropic modelling and the Fréchet derivative computations, which are the pivotal components of nonlinear resistivity anisotropy inversion. We adopt the Gaussian quadrature grid method to design the new anisotropic modelling and apply the perturbation analysis to compute the sensitivities (Fréchet derivative) for six 2D anisotropic cases. With the designed synthetic models, we carry out the numerical experiments with three multi-electrode surveying configurations, which are DD, GD and SC array. What’s more, we present six resistivity cases to discuss the anisotropic modelling and show the sensitivity patterns of the three arrays with the Fréchet derivatives. In a conclusion, the DD array can characterize the anisotropic structures better and the sensitivities can reflect the changes from the dip angle and the strike of the plane the stratification.
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2D Gravity Inversion Using Particle Swarm Optimization Method
Authors D. Darisma, U. Said and W. SrigutomoSummaryParticle swarm optimization (PSO) is an optimization technique inspired by the social behavior of individuals in nature (swarms). In this study, we have been developed and applied the technique to the gravity anomaly data. PSO algorithm was tested on syntethic data with 10% and 20% noise, and without noise. The syntethic gravity data was generated with finite rectangular prims that have density contrast with background. The inversion shows that calculated gravity anomaly and observed gravity anomaly are matched well. In fact, the challenge in PSO inversion is to determine the suitable value of the controlling parameters (i.e. inetia weight, cognitive parameter, and social parameter). But trial experiment shows that with the exact controlling parameter value, we could get a good inversion result that close to the model.
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Ambient Noise Tomography beneath the Gotvand-e Olya Reservoir (South-west of Iran)
Authors M.R. Ebrahimi and M. TatarSummaryIn order to define the precise shallow velocity structure beneath the second largest dam reservoir in Iran and to understand the loading effects on the underlying crust, the shear wave velocity of the shallow structure beneath the Gotvand-e Olya reservoir is determined using continuous data from 10 stations of a local network, installed to monitor the induced seismicity in the region surrounding the Gotvand dam for potential hazard. We obtained Rayleigh waves from cross-correlation of waveforms recorded 10 months before and 15 months after impoundment of the Gotvand reservoir and calculated the group velocity from dispersion analysis in the period range 2–8 s. The group velocity dispersion curves are used to produce 2D group velocity tomographic maps. The obtained results at short periods are well correlated with subsurface geological features and delineate distinct low- and high-velocity zones separated mainly by geological boundaries, indicating on capability of the Ambient Noise Tomography (ANT) technique for detailed study of the velocity structure and lithology at the shallow depth using continuous data from dense local seismic network.
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Quick Inversion of Multi-configuration Electromagnetic Induction Data Using Cumulative Response Functions
Authors F.C.M. Andrade and T. FischerSummaryIn this paper we present a quick method for one-dimensional inversion of multi-configuration electromagnetic induction data, obtained by instruments operating at low induction numbers, using cumulative response curves. As it is very fast and easily programmed it can be used when a real-time quick inversion in the field is desired and as a good initial guess model estimation for more sophisticated inversion techniques. In the proposed technique we make use of several measurements of apparent conductivity, performed with different transmitter-receiver dipoles configurations in a same location to estimate a one-dimensional model where the number of layers is equal to the number of measurements. The depths of the bottom of the layers are estimated as the depths of investigation of each configuration measurement. The conductivities of the first two layers are obtained by solving the linear system formed by the forward modelling equations for computing the apparent conductivity using the cumulative response functions for the two first configurations measurements. The conductivities of the remaining layers are obtained recursively using the previous estimated conductivities and the data measured by the following configurations using the same approach.
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Modelling the Influence of Ground Surface Relief on Electrical Sounding Curves and 2D Inversion Results
Authors B. Mukanova, I.N. Modin, T. Mirgalikyzy and K. BaranchukSummaryThe direct problem of electrical sounding of a medium with a ground surface is solved by the Integral Equations Method. The numerical method is based on the triangulation of the computational domain, adapted to the shape of the relief and the measurements line. The numerical algorithm is tested by comparing results with the known solution for horizontally layered media and by checking the fulfillment of the "reciprocity principle". The results of simulations have also been tested in artificial physical models. Then simulations are carried out for a two-layered media with a relief of the surface. Synthetic measured data have been obtained for a 2D relief form with the underlying layer at given depth h and resistivity p2. The quantitative effects of the influence of the relief form and media parameters (depth h, resistivities p1 and p2) to the apparent resistivity curves are established. Then synthetic data are entered into 2D inversion programs. Calculations show that the apparent resistivity anomalies lead to significant distortions of the interpretation results. Modelling on the base of Integral Equations Method allows one to estimate the level of false anomalies that appear due to topography.
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Geophysical and Geotechnical Characteristics of Champlain Sea Sediments in the Ottawa Valley, Canada
Authors H. Crow, G.A. Oldenborger, A.J.-M. Pugin, J.A. Hunter and B. DietikerSummaryThe soft Champlain Sea sediments of the Ottawa Valley, Canada are susceptible to earthquake-triggered ground failure and contribute to significant amplification of earthquake shaking. We investigate the geophysical and geotechnical properties of Champlain Sea sediments and the underlying shape of the bedrock basin. The objective of the multidisciplinary approach is to characterize the geophysical and geotechnical signatures of high sensitivity clay and silt, and to improve understanding of how these sediments respond to earthquake shaking. Geophysical techniques employed in this study include microtremor recordings, high-resolution seismic profiling, electrical resistivity imaging, and downhole geophysical logging. Geophysical and geotechnical data suggest a bedrock basin up to 98 m deep with a soft sediment fill that exhibits localized evidence of leaching and high sensitivity. Results are consistent with the presence of retrogressive landslide scars in the Breckenridge study area.
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The TOPSOIL Project - Integrated Approach of Near Surface Geophysics and Groundwater Modelling
Authors H. Wiederhold, M.A. Rahman, M. Grinat, R. Kirsch and W. ScheerSummaryTo ensure a sustainable freshwater supply good knowledge of the aquifer system is essential. Especially in coastal areas water quality is threatened by seawater intrusion and extensive withdrawals. The aim of our study is an integrated approach of geophysical methods and groundwater modelling to provide the data base for groundwater management strategies. The study area is located in North-Western Germany, where aeroelectromagnetic data are available. Additionally, ground based geophysical measurements for aquifer structure and properties are planned (e.g., 2D electrical resistivity, magnetic resonance soundings, ground-penetrating radar, seismic reflection profiles).
The study is in progress and part of the INTERREG North Sea Programme project TOPSOIL.
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Cluster Analysis for Cavity Detection Using Seismic Refraction and Electrical Resistivity Tomography
Authors P. Capizzi, R. Martorana, A. Carollo and M. VattanoSummaryGeophysical methods (in particular ERT technique) constitute an excellent tool for the detection of buried cavities. However the integration approach of e different geophysical methods could minimize the ambiguity of geophysical interpretation of the buried cavity. The technique of electrical tomography has been joined to the technique of seismic refraction tomography in order to obtain more robust interpretations. Many tests have been carried out using synthetic data and experimental ones. It was finally used a statistical approach based on cluster analysis of the P-wave velocity, the density of the seismic rays and the electrical resistivity of the synthetic and experimental models. Distribution maps of the cluster in multi-space were built, allowing to better define and interpret the anomalies of the subsoil.
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Geophysical Study of a Potential Source of Secondary Raw Materials - The Aijala Mine Tailings Area Southern Finland
Authors T. Valjus, T. Huotari, J. Lerssi, M. Markovaara-Koivisto and T. TarvainenSummaryWe describe here a tailings ponds’ potential to be a source of secondary raw minerals. This tailings pond was targeted as a study site because two mines, Aijala and Metsämonttu, from which the tailings are from, have been closed several decades ago, and therefore the tailings material might contain significant amounts of minerals which could be utilized with the modern processes. Geophysical measurements of gravity, magnetic, electromagnetic and electrical resistivity tomography were made to find out the dimensions and the inner structure of the tailings pond. By combining the results of geophysics and geochemistry sampling we estimated the mineral reserves and the amount of metals (Cu, Zn, Ag and Pb) within the tailings material. The Aijala tailings pond is one of the Finnish pilot areas of EU funded SMART GROUND project with focuses on the secondary raw material.
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