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6th Congress of the Balkan Geophysical Society
- Conference date: 03 Oct 2011 - 06 Oct 2011
- Location: Budapest, Hungary
- Published: 03 October 2011
81 - 100 of 158 results
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Determination of Site Response Functions in Yalova City with Microtremor Data
Authors S. Tekebaş and E. YalçinkayaIn recent years, at the determination of the soil response function, microtremor method is a most-preferred one which offers properties such as recording at short time and having no requirement of using any source. While microtremor method is considerably successful at the determination of resonance frequency, it is not successful at the assessment of soil amplification. Within the context of study, the microtremor measurements were taken at 81 total stations at Yalova and around (Altınova, Çiftlikköy and Çınarcık). Measurements were collected with CMG 6-TD seismometer at four different times in October, January, April and July. The horizontal/vertical spectral raitos were computed by using Nakamura (1989) method from these data and HVSR curves were derived. The obtained curves are evaluated with the geology and Yalova’s soil properties are tried to be determined. Few of the measurement points which have a clear peak and complex characteristics of H/V curves in Yalova point out the sediment discontinuties in lateral and vertical direction, resulting in 2D or 3D site effects. No soil-structure resonance were determined in Çınarcık, Hacımehmet, Çiftlikköy where the worst damage occured during the 17 August 1999.
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What is the Information Content of the Near Surface Debris Distribution?
More LessFormation of surface depressions is a significant geological hazard. Prediction of future sinkholes in buried karstic areas needs knowledge about the subsurface. In order to determine the varying topography of the karstifiable bedrock (in Bakony Mts, Hungary), we carried out multielectrode measurements. Due to the hard field conditions, the bedrock depth could not be detected. The resistivity anomalies in some places had a seasonal variation (low-resistivity in springtime, high-resistivity in the end of summer); therefore we interpreted the springtime resistivity lows as indicators of locations with high water content, that is as high porosity, saturated with water. At the same time, when pushing the current- and potential electrodes into the ground, we discovered a regularity in the areal distribution of the soil's rock debris content. Therefore we carried out a systematic electrode-pricking experiment, and categorized the soil's "toughness" corresponding to soft penetration, or blockage within the upper 30 cm. We have found a close relationship between the locations of resistivity- and the soil's toughness extremes. From some epikarstic features we think that high "pricking probe" values indicate smaller depths of the bedrock.
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Different Alternatives of Surface Waves Data Inversion. Applications on Environmental and Geotechnical Case Studies
Authors G.S. Kritikakis and A. VafidisThe inversion of Rayleigh surface waves dispersion curves exhibits the last few years rapid development in geotechnical and environmental geophysics. This study stresses on the demonstration of different alternatives of surface waves data inversion. The implemented algorithms (kriSIS) consist of several inversion techniques such as the usage of Quasi-Newton methods, the minimization of L1 or L2 norms, the application of smoothing, damping and blocky constraints and their combinations, as well as weighting inversion using data errors and/or the values of Jacobian matrix. Furthermore, any a-priori geophysical or/and geotechnical information can be taken in to account during the inversion. Two selected inversion techniques (damping and combination of blocky constraint with L1 norm minimization), were applied at two areas of environmental and geotechnical interest. This study indicates that the choice of the most appropriate inversion technique is crucial for any high resolution study.
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Seismic Geotechnical Site Characterization by MASW-REMI Method: Importance of Higher Modes of Rayleigh Waves
More LessIn the ’90 several researchers have realized that, when dealing with inversely dispersive sites, the MASW method based only on the fundamental mode can really cause erroneous Vs profiles, hence an erroneous seismic site characterization. When dealing with inversely dispersive sites ( i.e. sites where stiffness discontinuities exist, soft layers trapped between stiffer layers or viceversa stiff layers trapped between softer layers) higher modes of Rayleigh waves must be combined together with the fundamental mode to calculate the effective or apparent dispersion curve (Lai 1998, Roma 2001-2002-2006), in order to achieve a reliable Vs profile and a reliable seismic site characterization. It is not sufficient to calculate the numerical higher modes and use them separately for the inversion process, because it is practically impossible to distinguish the experimental higher modes from the field data in the geotechnical scale. It is well known that the apparent experimental dispersion curve that is determined from the field data is the result of a superposition of the several higher modes. In this article the potentialities of a new algorithm (www.masw.it, Roma 2001) that calculates the apparent dispersion curve using all higher modes are shown into an application to a real case.
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Integrated Geological-Geophysical Studies on Regionalization of Cities Mamuras, Lac, Milot and Fushe Kruje
More LessIn this paper we have intention to demonstrate the capacity of geophysical methods (electrical resistivity methods) to help in the more accurate way in these studies. In this case, some results achieved through electric resistance tomography method will be demonstrate, completed for the geological-engineering zonation of Milot, Lac, Mamuras and Fush Kruja, cities.
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Aplication of Geophysical Methods in Investigation
More LessKarstic phenomenon of carbonated geological formations is very developed in some parts of Albania. The results taken from the integrated geophysical methods for the study of karst phenomenon show that the most effective methods are: resistivity surveying with profile arrays, resistivity surveying with array profiles in combination with VES method, SP method, IP(Induced Polarization), gravimetric micro method. These methods have made possible the detection of karstic zones, with fresh water content and the cavities that present risk for private and public building.
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Complex Geophysical Investigation (CPT, Seismic Reflection and Tomograpy) of the Sliding Loess Wall along the Danuber River
Authors A. Cs. Kovács, T. Gúthy, E. Hegedűs, T. Bodoky, R. Csabafi and I. TörökA 30 to 35 m wide slice of a 100m height loess wall sank more than 10 m at the bank of the Danube near Dunaszekcső (Hungary) on 12th of February, 2008. Eötvös Lorand Geophysical Institute (ELGI) was requested a geophysical investigation of the area. ELGI installed a system of six continuously operating seismic stations to detect the seismic micro-emissions. Two main source areas of seismic micro-emission were allocated after the data analysis. We made four points of CPT a depth of 12 m on the bank of the Danube. We have concluded that the movement of the loess wall was caused not by a sliding phenomenon. We used vibrator as a source and 121 units of RefTek 125 single channel autonomous seismic recorder to make two seismic lines beneath and above the loess wall. Based on the structural image from seismic tomography and reflection sections sedimentary layers of different thicknesses can be found on the old basement up to the level of the river Danube. The anomalies of the two profiles mark out a tectonic zone running in an approximately E-W direction.
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Engineering Geophysical Study of Active Slides in the Mediaeval Castle and Kruja City, Albania
Authors P.L. Leka, F.V. Vinçani, P.K. Kosho and P.N. NaçoThe study region is part of Kruja tectonic zone and represents a syncline structure. City of Kruja has objects with architectural, historical and museum values and is built on Quaternary deposits, on the slopes with inclines 20-100, represented by lithological formations: colluvial, eluvial, deluvial and proluvial. Colluvial deposits represented by slope breccias with values of 30 m thickness are stable in facing of geodynamic phenomena. Deluvial deposits consist of clay and sand combination up to 5 m thickness, unstable and in the presence of groundwaters generate slides, while eluvial ones allow circulation of rainfall waters and weaken the contact of clay basement. Activity of erosion phenomena, neotectonic, tectonic movements in the areas of flisch spreading in this city, has brought the slides, crashes, damage to roads, cracks or demolition of houses as well as detachment of a part of the massive rock, on which lies the museum castle of "George Kastriot Scanderbeg
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Imaging Sand Dunes at Kedrodasos Coastal Area, Crete, Greece
Authors A. Vafidis, S. Zannetidis, N. Economou, H. Hamdan, P. Nyktas, G. Kazakis, D. Ghosn and E. RemoundouIn this work, we present preliminary results from a geophysical survey conducted at Kedrodasos, south Crete, Greece. The scope of this survey is to characterize the subsurface at the Kedrodasos Juniperus trees forest. We used GPR and electrical tomography to map the root system of these trees and to image the sand dunes. We used three methods for the inversion of the resistivity data. We applied deterministic deconvolution on the GPR data and employed a reflected wave from a lab experiment as reference wavelet. The thickness of the sand dunes does not exceed 2 m. Low resistivity regions with abundance of diffracted EM waves are attributed to the juniperous trees root system zones.
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Applied of Electrical Resistivity Method on Concrete Structures
Authors S. Altundaş and N. CoşkunNowadays, non-destructive testing (NDT) methods such as electrical resistivity method plays important role in the evaluation and testing of civil engineering structures. The aim of the study is to give basic principles of electrical resistivity method and their limitations in the structural evaluation programme and provide information about agreed standards that obtained various concrete materials. For this reason, in this study, electrical resistivity method was used to determine that the quality of the concrete and reinforcement within the concrete situation and position. The five different cylindrical concrete models with the same dimension (15x30 cm) are prepared for this study. Iron pieces, sponges and rebar in different size are put into the concrete to determine the resistivity responses of the models. After that, the concrete models are incubated approximately 21 days in a tank filled with water for gaining strength. The resistivity measurements are carried out on each cylinder model in three profiles. On the cylinder models, Wenner and Dipole-Dipole arrays used to obtain data, and interpreted using 2D inversion programme (DC2dTree, developed by Thomas Günther).
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Seismoacoustics in Geotechnical Boreholes for Estimation of Adjoining Soil Properties
By V.P. LisinThe possibilities of seismoacoustic investigations data in geotechnical boreholes using as parametrical for interpretation and increasing of reliability on-land 2D shallow seismic are considered. For these goals the results of a vertical seismoacoustic profiling, obtaining by essentially simple technique in comparison with crosshole investigation, are more preferable.
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Assessment of the Site Effects Based on Earthquake Recordings and in Situ Measurements in Bucharest, Romania
Authors A. Bala, A. Aldea, S.F. Balan and C. ArionWithin the NATO Science for Peace Project 981882 “Site-effect analyses for the earthquake-endangered metropolis Bucharest, Romania” we obtain a unique, homogeneous dataset of seismic, soil-mechanic and elasto-dynamic parameters. Ten 50 m deep boreholes are drilled in the metropolitan area of Bucharest in order to obtain cores for dynamic tests and vertical seismic profiles for an updated microzonation map related to earthquake wave amplification. The boreholes are placed near former or existing seismic station sites to allow a direct comparison and calibration of the borehole data with actual seismological measurements. A database is assembled which contains P- and S-wave velocity, density, geotechnical parameters measured at rock samples and geological characteristics for each sedimentary layer.
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Investigation of the Geological Structures of Kozlupinar and Bentpinar (Bağbaşi-Denizli) Water Source System by Using the
Authors A. Aydin, S. Tasdelen and D. Tanik DenisVery important water sources of Denizli city which are Kozlupınar and Bentpınar springs where take place between Pamukkale University and the Bağbaşı village have been investigated to find the feeding directions of groundwater and to obtain the fresh water for near counties. Those springs are the East part of the Aegean horst and graben systems. In the drainage systems of Gökpınar dams, those springs altitude of topography is high and the Sothern site and along the North Slope of the Bağbaşı village, they take place on the top of the slope debris and some deposited cones. Geoelectric and electromagnetic methods have been used to investigate the affect of drainage and urban area on the fresh water in the county of Sarayköy. Vertical electrical sounding has been performed on 48 points and GPR method was carried out about 6.4 km horizontally using georadar. As a result of hydro-geological and geophysical studies, affective feeding area of the springs is investigated in the area. This study may be the good example to investigate the feeding direction and the location of the springs for similar type of projects.
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Physical - Mechanical and Sanitary Indicators in Drinking Waters and in two Mineral Waters of Lushnja District
By A. DodonaThe study results presented in the paper aimed to deal with drinking water quality of the city and of the district and highlight the characteristics of two mineral water of Lushnja district in the Western Central Albania, according to the “International standards of drinking water” (WHO). The study covering 25 district waterworks, supplying more than 50% of the population. In their waters are determined a large number of indicators, divided into separate groups which are: the odour, taste, colour, temperature, pH, radioactivity and natural radio elements, free carbonic gas, sulphur hydrogen, free chlorine, dissolved oxygen, the total and mineral acidity, total alkalinity, ammonium, biochemical oxygen demand, nitrites, oxidation, nitrates, pesticides, phenols, cyanides, hardness, carbonates, bicarbonates, phosphates, metasilicilic acid, total dissolved solids TDS, anion-cationic composition, fluoride, iodide, iron, zinc, lead, manganese, copper, arsenic and boron. Spectral control have been made for Co, Cd, Hg, Cr, Ni, V, Mo, Se, etc., radiometric and gamma-spectrometric control is made for natural water radio-elements U, Ra, Rn, Th, and bacteriological analyses. Has been observed also the relationship between the chemical composition of groundwater and geological setting of the aquifers.
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Geophysical Detection of Marine Intrusions in Black Sea
Authors F. Chitea, P. Georgescu and D. IoaneCommunities living in coastal areas depend in a great extent on the fresh water resources exploited from aquifers which are usually in a natural hydrodynamic equilibrium with the sea water. The contamination of fresh water with marine salty water determines a significant increase in the aquifers electric conductivity, allowing an efficient application of resistivity methods in detecting and monitoring the marine intrusions. We present case studies from Romania (Costinesti and Vama Veche areas, southern Dobrogea) based on older vertical electric soundings (VES) and recent electric resistivity tomography (ERT) measurements, relevant for the detection and monitoring of coastal marine intrusions. The results of the geophysical investigations are mostly represented as apparent resistivity but also as inverted cross sections, both illustrating by means of resistivity anomalies the spatial development and evolution in time of the marine intrusions.
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Evaluation of Ground Vibrations Generated by Sheet-pile Driving
Authors M. Lednicka and Z. KalabThe article describes basic principles of vibration generation and propagation through the surroundings when vibratory pile-drivers are used in the construction of a sheet pile wall. These vibrations fall into technical seismicity and contribute to the seismic load of engineering structures situated in the vicinity of such walls under construction. Further, the article presents results of the measurement of effects of these vibrations during the making of the sheet pile wall during the construction of a new building of VŠB – Technical university of Ostrava. A result of the measurement is the assessment of the data in time-frequency domain while using special “Spectra analyzer” software. Evaluation of vibration attenuation in the given earth environment and the values of the oscillation velocity amplitudes depending on the distance from the source of vibration for different frequency ranges are also presented.
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The Pressure Dependence of Acoustic Velocity – a New Petrophysical Model
Authors H. Szegedi, J. Somogyi Molnár and M. DobrókaPressure dependence of acoustic waves is an extensively explored rock physical problem. Knowledge of the phenomena of pressure dependence is an important prerequisite for relating laboratory meas-urements to in-situ rock properties, and for interpreting seismic measurements in terms of subsurface petrophysical parameters. Therefore it’s expedient to develop a petrophysical model based on simple physical assumptions which describes the relationship between acoustic velocity and pressure. The model is based on the idea that microcracks are opened and closed besides different pressure states. The model was applied on own acoustic velocity data sets and also data sets measured by Yu et al. as well as Xu et al. The material parameters of the models are determined by using inversion method and the laboratory measurements were compared to the theoretical data. The theoretical data matched accurately with measured data proving that the petrophysical model applies well in practice.
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Interval Inversion of Wellbore Data for Characterizing Metamorphic Hydrocarbon Reservoirs
Authors É.E. Tolnai and N.P. SzaboIn investigating multi-mineral rocks, the nonlinear well-logging inverse problem becomes an underdetermined or at the best a very narrow type of overdetermined problem, which cannot be treated by conventional local (point-by-point) inversion methods with satisfactory accuracy and reliability. In order to determine the unknown petrophysical model composed of many parameters (i.e. volume of matrix components, water saturation, clay content, primer and secondary porosity) with no ambiguity, it is essential using a joint inversion process. The interval inversion method is a special kind of joint inversion technique, which inverts data of a greater depth interval simultaneously in a highly overdetermined inversion procedure. Having used interval inversion method with success for the case of shaly sand environments, now the efficiency of the global optimization based interval inversion method is demonstrated for the case of hydrocarbon-bearing rocks with complex lithology.
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Rock Body Classification made from Geophysical Measurements
By S. HegedűsA very effective and prompt rock body classification can be served from the resistivity and acoustic wave measurements, which complements and highly helps to evaluate the information from the core investigation and pressure tests.
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On the Correlation of Seismic Noise in Izmir City, Aegean Region of Turkey: Preliminary Results
Authors M. Kececioglu, F.J. Chavez-Garcia, E. Gok, U. Ceken and O. PolatSeismic risk in the Eastern part of Turkey is high due to active tectonics in the region. Recently, a new seismic network was installed in Izmir region. Because the objective was to analyze seismic response, not all stations were installed on firm rock. Rather, the different geologic formation at the surface was sampled by the 16 sites. The stations are high quality, digital accelerographs by Guralp, writing continuously. Preliminary analysis of earthquake data recorded to date has been presented in Gok (2011). The results gave some estimate of transfer functions for the different sites. However, no information is available on the subsoil structure. We need to have the structure to compute response and compare with observed seismic response. For this reason, we have taken advantage of the continuous recording at the array. Seismic noise is analyzed in this paper using correlation to estimate Green's function between station pairs. The preliminary results are encouraging. We are able to estimate group velocities between stations, although signal-to-noise ratios are small and the frequency band of the pulses is restricted. In spite of this, we present a preliminary map of velocity variation as a function of path for the Izmir gulf region.
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