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8th Congress of the Balkan Geophysical Society
- Conference date: October 5-8, 2015
- Location: Chania, Greece
- Published: 05 October 2015
1 - 20 of 124 results
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Refraction and Amplitude Tomography Based Methodologies on Evaluation of Engineering Properties of Rocks - A Case Study
Authors A.E. Babacan and K. GelisliSummaryThe main aim of this study was the reveal of internal structures and engineering properties of basalt bedrock aged Eocene-Neocene, north of Eastern Pontides, Turkey. In selected area for this purpose, the seismic data were collected at total 7 profiles. A shallow refraction and amplitude attenuation tomography survey in study area was performed to mapping of Vp velocities and attenuation coefficient for civil engineering plans. In order to determine shear wave velocity (Vs) of study area, multichannel analysis of surface wave (MASW) in was also used. The Evaluation results show that the study area has three layers. The upper layer was interpreted as topsoil having a P velocity range from 400 to 800 m/s. The middle layer was interpreted as weathering basalt having a wave velocity range from 1200 to 1600 m/s. The bedrock was interpreted as massive basalt. P-wave seismic velocities of this bedrock range from 1800 to 2800 m/s. The average Vs 30 velocity was found 730 m/s from MASW. Attenuation coefficient is an important parameter to identification rock mass structure and 1/α value of weathering and massive basalt was changed between 5 and 15. During site selection, it has to determine to engineering properties of foundation rock.
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A Rapid Mapping of Sarıçiçek Pluton from In-situ Gamma Ray Measurements
Authors S. Altundas and H. ÇinarSummaryThe concentrations of equivalent eU, eTh, K% and dose rate values were measured using in-situ gamma-ray survey in order to map rapidly the surface geology of the Sarıçiçek pluton and its surrounding area. Gamma-ray spectrometric data were collected with a 512-channel portable gamma-ray spectrometer (NaI (Tl) cyrstal) at 265 points in which duration for a single point measurement is 5 minutes. The average activity concentrations of 238U, 232Th, 40K and dose rate obtained in this study are 38.97 Bq/kg, 50.56 Bq/kg, 935.267Bq/kg and 88.78 nGy/h, respectively. Although distinct radioactive anomalies were found in the studied area, the radiometric values showed some minor variations with slightly higher values than the normal level. As the result of this study, the average values of the absorbed gamma dose rate in air, radium equivalent activity, annual effective dose rate and the external hazard index were also calculated and examined in terms of radiologic hazard in this area. Consequently, all of the radiometric parameters are in good agreement with the regional surface geology of the Sarıçiçek pluton and its surrounding formation and there is no significant radiologic risk for humans and environment in and around this area.
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The First Steps for a Joint Romanian-Bulgarian Regional Early-Warning System for Marine Geohazards
Authors N.D. Dobrev, O.V. Dimitrov, G.P. Nikolov and K.S. KostovSummaryAn overview on the main hazardous geological processes endangered the Romanian-Bulgarian Black Sea coast with emphasize on hazards related to Bulgarian side, and goals and objectives of the Cross border project MARINGEOHAZARD whose purpose is to create key core components of a joint early warning monitoring system approved on both countries. The basic geohazards concerning Bulgarian part of the coast are presented. This includes historical strong earthquakes with tsunamis. The effects from the catastrophic earthquake with M7.2 occurred on 31 March 1901 near Kaliakra Cape have been described. The area is characteristic with large size landslide affecting strongly the North Bulgarian shoreline. The installed monitoring equipment included network of complex automatic marine measurement equipment, onshore network of online GNSS stations, extensometers, marine seismic monitoring equipment, etc. The first results obtained from 3D extensometric monitoring performed around Kaliakra Cape have been presented.
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Nonlinear Dynamics of Regional Cyclogenesis with Wind Speed Variations
Authors N.S. Erokhin, N.N. Zolnikova, L.A. Mikhailovskaya and R.S. ShkevovSummaryA numerical analysis of a self—consistent small parametric model (SPM) of a regional large scale cyclogenesis (RLSC) has been performed by usage of connected nonlinear equations for mean wind speed and ocean surface temperature in the tropical cyclone (TC) zone. These equations may describe the different scenario of temporal dynamics of a powerful atmospheric vortex during its full life cycle. By means of numerical calculations it is shown that relevant choice of SPM’s incoming parameters allows to obtain the seasonal behavior of regional LLSC with a given number of TC during the active season. In addition, the model allows describe the wind speed variations within the TC. So in the reference frame of the nonlinear small parametric model it is possible to study the features of RLSC’s temporal dynamics during the active season in the region given, to analyze the relationship between regional cyclogenesis characteristics and different external factors like the space weather.
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Determination of the Amplitude Values with Nakamura (H/V) Method and Standard Spectral Ratio (Ssr) Method at Ktu Campus
Authors Y.B. Beker, N. Sayil and Ö. AkinSummaryMicrotremor method used for engineering seismology is very important for determining of dynamic ground parameters and its variations. Method based on frequency of horizontal and vertical component microtremor records provides to quick and economical estimation of dynamic ground parameters. In this study, Nakamura (H/V) method and Standard Spectral Ratio (SSR) method have been applied to microtremor records taken with CMG-6TD three component broad band velocity seismometers in six profile with the aim of determining ground amplification of Karadeniz Technical University Campus area. The amplification maps of the study area are generated to the results of Nakamura (H/V) method and Standard Spectral Ratio (SSR) method and the results have been compared.
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Measuring Natural Radiation Backgrounds for Natural Hazard Evaluation in the Aspiring Buzău Land Geopark, Romania
Authors R.G. Popa and R. StochiciSummaryBuzău Land aspiring Geopark is a 1036km2 territory located in Romania, at the Carpathians Bend, in the close proximity of the Vrancea seismogenic area. Our work deals with natural hazards and risk in the aspiring Geopark territory. One of the hazards approached, which is the subject of this paper, refers to the exposure to natural radiation of inhabitants and visitors alike. Our work is still in progress, and we shall present its development so far. The measured values for radioactivity dose vary between 7.82 nSv/h and 56.83 nSv/h. Th levels vary between 1.38 ppm and 11.69 ppm, U levels vary between 0.31 ppm and 4.5 ppm and K levels vary between 0.32% and 2.12%. So far it seems that the natural radioactivity dose does not pose risk towards the inhabitants of Buzău Land Geopark or to its visitors, as the dose values are about 10 times smaller than the world average. We shall continue our measurements in order to optimally cover the entire territory and all lithological units, to have a comprehensive overview of the distribution of background radioactivity levels.
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Remote Sensing Observations of the Total Solar Eclipse and Incident Solar Radiation
Authors D. Krezhova, A. Krumov and K. KrezhovSummaryThe results from ground-based remote sensing investigations of changes of the environmental conditions (dramatic brightness reduction, local cloudiness, behaviour of the incident solar radiation) during the total solar eclipse on 29 March 2006 are presented. Series of digital images of the solar disk and corona as well as of a near-sun sky area were obtained during the all eclipse phases using a photometric CCD camera. Synchronous data for the dramatic changes and spectral behaviour of the incident solar radiation were collected by means of a portable fiber-optic spectrometer in the spectral range 350–1100 nm. The images were used to trace back the atmospheric conditions during the spectrometric measurements and to match the spectral data to the eclipse phases. The appeared fluctuations in the spectral behaviour of the solar radiation within several time intervals after the eclipse totality were caused by appearance of fine cloudy structures in front of the solar disk. We have found also changes in the spectral distribution of the solar radiation before and after the eclipse totality expressed in decrease of the solar radiation at the lower wavelengths and an increase in the spectral range after the spectra maximum due to the limb darkening effect.
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Imaging of Alpine and Post-Alpine Formations Using ERT at Loutsa- Remeri Open Pit Mine, Scourta, Viotia, Greece
Authors A. Vafidis, N. Andronikidis, H. Hamdan, I. Pyliotis, G. Panagopoulos, E. Manoutsoglou, L. Kikidis and N. BotosSummaryA geophysical survey carried out at Scourta plateau in Central Greece employed the electrical tomography method in order to image the interface between Alpine and Post-Alpine formations and estimate the thickness of Terra Rossa deposits. The later are crucial for TITAN-SA cement company open pit mine. This mine provides row materials for cement production. This survey is related with future extension plan of the existing Loutsa-Remeri open pit mine. Scourta is an active polje and is filled with a thick Terra Rossa deposit which is a row material for cement industry. The geophysical survey revealed two distinct layers, the upper is characterized by lower resistivity values (less than 20 Ωm), minimum thickness to the east (25 m) and maximum thickness at least 50 m and is attributed to Terra Rossa deposits. The underlying layer exhibits higher resistivity values (more than 70 Ωm) and is attributed to karstified carbonate relief. The variation of the polje depth is accosiated with tectonokarstic processes. The E-W direction fault system delineates the karstic structure and the N-S ridge in the east part of the survey area is delineated by N-S direction faults.
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Numerical Study of the Air Quality in the City of Sofia
Authors I. Georgieva, G. Gadzhev, K. Ganev, M. Prodanova, D. Syrakov and N. MiloshevSummarySome extensive numerical simulations of the atmospheric composition fields in the city of Sofia have been recently performed. The simulations were carried out using the following set of models: the model WRF used as meteorological pre-processor; CMAQ - the Community Multiscale Air Quality System — the chemical transport model; SMOKE - the Sparse Matrix Operator Kernel Emissions Modelling System — the emission model. As the NCEP Global Analysis Data with 1 degree resolution was used as meteorological background, the WRF and CMAQ nesting capabilities were applied for downscaling the simulations to a 1 km resolution over Sofia. The national emission inventory was used as an emission input for Bulgaria, while outside the country the emissions were taken from the TNO inventory. Special pre-processing procedures are created for introducing temporal profiles and speciation of the emissions. The biogenic emissions of VOC are estimated by the model SMOKE. Different characteristics of the numerically obtained concentration fields will be demonstrated in the present paper.
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Determination of Buildings Period and Vulnerability Index Using Microtremor Measurements
More LessSummaryMicroremor data has an important role on determining the ground dominant periods. Another way of use of the method is the application on the constructed buildings for investigating the strength and periods of each floor. It is possible to define the period of each floor and calculate the floor spectral ratio (FSR) parameter using microtremor data. This parameter is being used to estimate the transfer function (amplification, natural frequency and vulnerability index) of the buildings. In this study, microtremor data were collected in Folkart Towers which have a length of 200 m. The data were recorded at 14 floors for 40 minutes. The validation of frequencies were determined using FSR in order to obtain damping ratios accurately. The variation range and tendency between damping ratio and frequency of each floor with damping ratios and vulnerability indices, along with the preliminary influence factor, were presented and discussed. In addition, a fitting curve was plotted indicating the relation between the damping ratio and dominant natural frequencies of the floors. Furthermore, evaluation of strength, damping ratio, natural dominant frequency and vulnerability index of the building were estimated by interpreting microtremor data. The dominant frequencies of 44th, 22nd and 7th floors of the buildings were calculated as 0.4 Hz, 0.4 Hz–1Hz and 1.1 Hz respectively. It was determined that the buldings have 2 dominant periods. They are 1.1 Hz from 1st to 22nd floors and 0.4 Hz from 23 to 44th floors.
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Relationship Between Quasi Transfer Spectrums and Dynamic Amplification Factor
More LessSummaryQuasi Transfer Spectrums (QTS) and Dynamic soil amplification factor defining which ratio earthquake acceleration will reach the soil surface by changing is one of the most important factors in seismic risk studies. When computing the value of DAF at a point without a strong motion station, peak horizontal acceleration values at the bedrock and soil transfer function are needed. PGA value at the bedrock can be obtained by using either real seismic records or the earthquake scenario. However, the soil transfer function can be computed observationally and theoretically. Observational soil transfer function is defined by microtremor horizontal/vertical spectral ratio. In case of theoretical computation, the density belonging to the soil layers between the bedrock and the soil surface is used together with the change of P-S wave rates with the depth and the damping factor. In this study, the dynamic amplification factor has been computed for 57 points by using observational QTS obtained by microtremor horizontal/ vertical spectral ratio as well as the earthquake scenario. Also, theoretical soil transfer function at 1 point was obtained through spatial autocorrelation method study and determined to be compatible with observational result.
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Analysis of Reliability of the Microtremor Method
More LessSummaryMicrotremor method has often been used for determination of the fundamental frequency of the sediments covering the bedrock. Relatively, it is easier to apply than drilling, cost-effective and reliable method and has become widespread recently. There are some important issues that need to be considered during the measurements such as cultural noise level, recording time and terrain conditions. It is possible to obtain reliable results from this method, if both data collection and processing stages were carried out adequately. With respect to the suggestions of SESAME Project, the reliability of H/V curves and the apex on the H/V curve representing a possible ground resonance frequency were investigated. There are 3 main suggestions of SESAME Project in order to determine the predominant period (T0) and investigate the reliability of H/ V curves. These conditions are determining suitable number of windows, number of periods should be more than 200 and according to f0 value, standard deviation (σ) of H/V curve should be less than 3 if f0<0.5 Hz and σ<2 if f0>0.5 Hz. Besides, at least 5 over 6 criteria of SESAME Project should be proved in order to obtain a reliable result from the calculated apex of a H/V curve. Thus, the apex of H/V curve can be accepted as a reliable peak and this proves the observer to determine reliable ground parameters as well. In this study, output file of the H/V curve obtained from the evaluation of the microtremor data using Geopsy software was evaluated by an Excel-based program to examine the criteria determined in the context of the SESAME Project. Also the flowchart of the algorithm is presented. Data were collected from the Bornova district of Izmir. The measurements were analysed and the results were interpreted.
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Geophysical Characterization of the Havuzlu Landslide in Artvin Dam Area, Eastern Turkey
Authors K. Gelisli, S. Goren, H. Ersoy and C. CelikSummaryThe Artvin Dam and hydroelectric power station that has been built on the Çoruh River will have an average of production 1 billion kWH per year. It is far 20 km from south-west of the Artvin Province (Eastern Turkey). Havuzlu Landslide is located in a slope in boundaries of the Havuzlu village on the Artvin dam reservoir. The Havuzlu Landslide which has complex structure and including groundwater is paleo-landslide. The structure of paleo-landslide, potential sliding surface, possible fractures, crushed zones, geotechnical properties of formations and situation of groundwater were investigated by 2D electrical resistivity imaging method, self-potential (SP) measurements, microtremor and boreholes data. To calculation of slope stability possible sliding surface was determined between the landslide material and bedrock. Distribution of landslide materials along vertical and horizontal directions was determined. Structure of landslide mass and bedrock were extremely heterogeneous. Silty-clay and saturated zones were identified in the landslide mass. The crushed zones were estimated on bedrock layer. In the landslide area was calculated slope stability for three selected profile was demonstrated to be unstable.
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Geophysical Investigation for Environmental and Geotechnical Projects in the Lavrion Technological and Cultural Park
Authors G. Apostolopoulos, A. Kallioras, G. Amolochitis and G. MakrisSummaryA tailored geophysical investigation was designed to provide useful information in two of the activities/ priorities of the Lavrion Technological and Cultural Park (LTCP): a) identification of optimal location for the construction of an advanced Soil-Aquifer-System (SAT) which will be used to monitor geo-purification processes within the unsaturated zone; b) detection and mapping of an old (abandoned) mining tunnel that is envisaged to serve the educational purposes of the LTCP. Electromagnetic measurements in a regional and local mode have given useful information as a reconnaissance method in the positioning of the best area for the first activity outlining mainly areas of problematic anthropogenic features. ERT method clarified in a great detail the underground features in order to better design the structures for the two activities/priorities of the LTCP.
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Fracture System Mapping Using Pressure Probe Method
Authors S. Szalai, M. Metwaly, K. Szokoli, Á. Tóth and V. WesztergomSummaryMechanically weak zones may arise e.g. due to rock realignment in the subsurface having an effect to the near surface-, or even to the surface sediments. If they are not directly seen from the surface a new method, the so-called pressure probe (Pre-P) method may be used to detect and characterise them. This method is presented on the example of the investigation of the fracture system of a landslide. Repeatability of the Pre-P measurements, adequate sampling distance, resolution of the method and the possible data processing steps are also investigated. We know from these investigations that: 1. there are consolidated zones on the slope side of the fractures whose broadness correlates with the broadness of the given fracture; 2. both the large and the small fractures follow each other periodically; 3. even the structure inside the blocks which belong to the large fractures can be well seen which refers to the very good resolution of the method. The here presented Pre-P method seems to be the most favourable tool to map the fracture system of such kind of landslides according to its resolution capacity, speed, simplicity of its application, the interpretation of the data and its costs.
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Geotechnical Characterization of a Tailing Pond Dam
Authors Zs. Pronay, E. Törös, G. Taller and P. TildySummaryThere are about 30 tailing ponds of different size situated in Hungary. One of them was broken in 2010 and about 40 km2 was flooded by red mud causing 10 casualties and 140 injured. Since this incident Mining Authorities are responsible for the regular inspection of the dams. For testing the available geophysical methods intensive field tests were completed by the Geological and Geophysical Institute of Hungary to help the Authorities.
In this presentation the geotechnical and geophysical investigation of a selected tailing dam will be discussed. To investigate the dam 2D and 3D multielectrode DC method together with P- and Rayleigh-wave seismics and CPTu sounding was applied. There were triaxial or direct shear laboratory tests on undisturbed core samples as well. The geotechnical and lab results were compared with the values calculated using the seismic velocities.
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Application of ERT to Map Earth Fissures at the Valtotnera Area (Amyntaion, NW Greece)
Authors P. Tsourlos, G. Vargemezis and I. FikosSummaryIn this work we present the results of the application of the electrical resistivity tomography (ERT) technique into the mapping of the fissures that appeared in the Valtonera area (Amyntaion Munisipality, NW Greece). The results of ERT provide a satisfactory explanation to justify the expression of surface cracks in specific areas and this approach can be used to provide areas that are likely to be associated to fissures in the future.
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Application of Electrical Resistivity Tomography Method to the Mapping of Explored Caves and Detection of Possible New Chambers: Case Studies from Greece
Authors G. Vargemezis, I. Fikos and P. TsourlosSummaryCave detection and mapping is one of the most common targets of the resistivity method since the infinite resistivity of the air filled void of the cave is at a high contrast to the resistivity of any geological structure. In the case studies presented in this work (Maroneia and Andritsa, Greece) the caves are formed in limestone because of the karstification in addition to the local tectonics.
The geophysical method applied in both case studies is the Electrical Resistivity Tomography (ERT). The existing chambers have been observed in the resistivity models and new chambers are detected.
However, resistivity values attributed to the caves are of wide range. In Maroneia values of several thousand of Ohm.m have been measured while in Andritsa the values characterizing the chambers are small (maximum of 1610 Ohm-m).
The different behaviour of resistivities can be explained by the different geological formation hosting the caves and emphasizes the need for calibration measurements. This can be overcome with ERT measurements on the same geological formation but far from the surveyed area in order to measure the resistivity of the formation itself. In this case a forward modelling will suggest the expected values in the presence of a void.
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Sedimenthological Model of Lom Lignite Basin (North Bulgaria) - Integrated Use of Geophysical and Geological Data
Authors M. Yaneva and S.B. ShanovSummaryThe sedimenthological Model of Lom Lignite Basin (North Bulgaria) is represented by a set of maps, elaborated for the principal geological layers (sedimentary complexes) on the base of integrated analysis of data from boreholes, seismic profiling, seismic well logging, and vertical electrical sounding.
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Development of an Earthquake Shake Map Routine with Low Cost Accelerometers: Preliminary Results
Authors G. Tanırcan, H. Alçık and Y. KayaSummaryVast amounts of high quality strong motion data are indispensable inputs of the analyses in the field of geotechnical and earthquake engineering however, high cost of installation of the strong motion systems constitutes the biggest obstacle for worldwide dissemination. Today, for a high quality system, about 10,000 USD budget per instruments is required. In recent years, MEMS based (micro-electro-mechanical systems) accelerometers have been used in seismological research-oriented studies as well as earthquake engineering oriented projects basically due to precision obtained in downsized instruments. In this study two accomplishments were done. In the first phase; MEMS based instruments available in the Institutes’ inventory were modified so as to be used for real time monitoring. In the second phase a Matlab based shake map routine was developed to calculate various ground motion parameters in per-second basis only after triggered by an event. Hence, synchronized real time data transfer from instruments served to create a rapid response network in an affordable way. Functionality of the software has been investigated through shake table tests. The successful realization of this product also allowed us to set up a test network at Tekirdag Province, the closest city to moderate size earthquake activities in central Marmara Sea.
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