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10th Congress of the Balkan Geophysical Society
- Conference date: September 18-22, 2019
- Location: Albena Resort, Bulgaria
- Published: 18 September 2019
1 - 20 of 64 results
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Preliminary results from analysis of geodetic data for the Northern Black Sea landslide “Momchilov rid”
Authors N. Dimitrov, I. Georgiev, M. Atanasova and A. IvanovSummaryThe study of landslides is of particular importance because these phenomena can lead to great material damage. Northern Black Sea coast is an important economic area and is driven by well-developed tourism. The region is affected by many landslides and it is important to monitor motions of the major landslides in the area. A preliminary study, based on data provided by Ministry of Regional Development and Public Works of the landslide processes in the area of “Momchilov rid” was made. Processed and analyzed are four epochs geodesic coordinates to solve for points velocities of the established geodetic control network.
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Preliminary results of Integrated Geophysical Surveying in an active landslide in Işıklar-Trabzon, Turkey
Authors M. Şenkaya, A.E. Babacan and H. KarslıSummaryIntegrated Geophysical Surveying has gain importance for landslide investigations, deciding the type of landslide, location of the possible sliding and failure zones, the interface between soil and bedrock, determining of water-containing zones, and lithological variation in lateral and vertical direction. This study presents preliminary results of the evaluation of seismic refraction tomography (SRT), multichannel analysis of surface wave (MASW), electrical resistivity tomography (ERT) and microtremor (HVSR) data collected in from an active landslide where is located in Işıklar locality of Maçka district in Trabzon province. From these data, 2D P-wave velocity and ERT sections, 1D S-wave velocity depth profile, and the values of predominant frequency and H/V amplitude of ground were obtained by using regular processes and inversion steps. Based on preliminary results, possible distribution of landslide materials in the horizontal and vertical directions was revealed and it is shown that the landslide materials with a thickness exceeding approximately 12 meters. Dominant materials of study area are composed of large and small blocky rocks and have a very complex structure. Moreover, the SRT and ERT sections show the presence of a valley-shaped structure and that the type of landslide is a combination of collapse-sliding.
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Rainfalls and groundwater influences on landslides in Northeast Bulgaria
Authors Y. Chapanov, M. Atanasova, T. Orehova and H. NikolovSummaryThe main reason of landslide activation is rising of groundwater, saturation by rain, water infiltration and snow melting. One part of landslides in Northeast Bulgaria starts after heavy rainfalls, as was evident during the last 20-year wet period. The interconnection between the landslides in Northeast Bulgaria, rainfalls and groundwater maxima is investigated by variations of discharge for spring near Kotel and groundwater levels in two dug wells near Balchik, precipitation from meteorological stations Sofia, Varna, Veliko Tarnovo and Kazanlak, and Palmer Drought Severity Index (PDSI). The periods of maxima of precipitation, PDSI and groundwater time series are compared with the registered occurrence of landslides. Some part of landslides occurs after groundwater maxima, other part – after intensive short-time rainfalls without significant change of groundwater levels. It is necessary to analyze time series of precipitation and PDSI in order to provide comprehensive landslide forecast. The groundwater levels follow almost exactly the PDSI variations, while the short time intensive rainfalls are presented as significant spikes in precipitation time series. The hazard risk of landslides on the territory of Bulgaria should be estimated by the maxima of PDSI, real meteorological data from stations located near the Black Sea coast and inside the territory.
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Geophysical Surveys for a Quarry Characterization - A Case Study in Konsko, Gevgelija
Authors I. Gjorgjeska and V. SesovSummaryGeophysical surveys by application of seismic refraction and shallow reflection method were carried out on the potential quarry location in Konsko, Gevgelija, R. North Macedonia.
The investigations were performed for defining of the seismo-geological structure, i.e., physical-mechanical characteristics of the rock mass constituting the structure of the terrain in conditions prior to excavation, and exploring the possibility for its use as a construction-technical material for a dam over Konska Reka river.
As a result of the investigations performed by application of seismic reflection, there were defined local disturbances and discontinuities that point to loose, cracked zones in the shallower as well as in the deeper layers of the terrain structure of the investigated location.
The seismic refraction method was used to define the variation of the Vp and Vs velocities of seismic waves down to a maximum depth of 30–50 meters. Defined with these investigations was the thickness of the surface layers composed of highly weathered and crushed rocks under the influence of external atmospheric conditions and also as a result of tectonic processes.
According to the generated 2D isopach map, the most critical zone belongs to the upper North-eastern part of the location
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Heavy rainfalls in Bulgaria due to solar activity and their possible influence on landslides
Authors Y. Chapanov, M. Atanasova and H. NikolovSummaryThe solar activity cycles affect various parameters of surface areas, including rains, snow covers, river streamflows and other hydrological cycles. These processes are due mainly to the total solar irradiance variations, followed by weather and climate changes. The interconnection between the solar cycles and decadal changes of rainfalls over Bulgaria is investigated by means of reconstructed Total Solar Irradiance TSI, precipitation from meteorological stations Sofia, Varna, and Palmer Drought Severity Index (PDSI) for the period 1899–2015. The decadal oscillations of precipitation and TSI with periods corresponding to the sunspots (11 years), solar magnetic cycle (22 years), equatorial solar asymmetry (45 years), Gleissberg cycle (70–100 years) and their harmonics are compared and analyzed. Models of decadal variations of PDSI and precipitation, based on solar cycles and harmonics, are created. The periods with rainfall and PDSI maxima are calculated on a century time span and a forecast of landslides is determined.
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Application of Electrical Resistivity Tomography and Induced Polarization for Identification of Underground Reinforced Concrete Structures
Authors I. Taleski and A. VelevskiSummaryApplicability of the Electrical Resistivity Tomography and Induced Polarization methods for detecting and identification of underground reinforced concrete structures was tested on an overpass foundation with three piers. Prime targets for this survey was detection and delineation of low resistivity and high phase angle difference zones, created by reinforced bars embeded in concrete structure. For the purposes of these investigations, 2 profiles laid along the piers were set up and joint resistivity and IP data was recorded and than processed. Interpreted sections give a very good results in detection and delineation on selected structure, which may provide valuable information that can be used in various engineerical applications.
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Detection of buried foundations in urban environment by Electrical Resistivity Tomography
Authors F. Chitea, D. Ioane, C. Tolbes, M.C. Calin and A. DiaconuSummaryDetection of buried remains of old structures is not always an easy target for electrical or electromagnetical methods as sometimes there is a low contrast between buried remains and embedded rocks or due the interference of modern infrastructure which makes difficult to isolate the buried remains signal or limits the deployment of geophysical profiles. In this paper, we present a successful case study, where local geophysical noise sources were overpassed by using ERT method. High-resolution 2D models allowed to locate buried remains of old facilities and even to reconstruct the footprint of an old building which displayed a complex “L” shape. The 3D ERT resulted model allowed to compare different sectors of the building, to extract the most probable foundation structure (different on two wings) and to analyze the construction rubble filling material.
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SEISMIC LOCATION OF COAL SEAM FAULTS IN UNDERGROUND COAL MINING
By O. SukhininaSummaryTo aid in coal seam faults exploration in the underground coal mines, a seismic location method based on multidirectional summation of reflected seam waves was developed. In contrast to the known method of controlled directional reception (CDR), it is proposed to calculate the time shifts between seismic records using not only the linear component of the hodograph of the reflected waves with a common source (or receiver) point, but also a hyperbolic component. The asymmetry of this hodograph, as well as the specifics of the placement of the seismic observation system in the mine workings, allow for a separate detection of the reflecting boundaries in the four sectors of the outer (relative to the observation system) part of the coal seam. The proposed method can be useful when a single mine working is utilized.
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Depth Estimation from Gravity Data Using Radial Amplitude Spectrum Method: Application on Dikili (İZMİR) Geothermal Field
More LessSummaryGravity method is a natural potential field method which is frequently used in geophysical investigations. The main principle of the method is to determine the buried structures in the ground by taking advantage of the changes in the vertical direction of gravity acceleration. There are many different methods developed to determine the depth of structures. In this study, the mean depth values of Bouguer gravity data obtained in Dikili district of İzmir province were determined using Radial Amplitude Power Spectrum Method (RAPSM) based on 2D Fourier transform. The greatest advantage of this method over the conventional power spectrum is that it works by determining the mean value of the cross-sections taken in different directions. Thus, it does not matter what direction the user takes the cross section and the depth of the structure can be determined more accurately. As a result of the application, the average depth values of the basement structure of the study area were determined. The topography of the basement structure varies between 320 m and 640 m in the region.
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A hidden caldera revealed from magnetotelluric data in Cappadocia region of central Turkey
Authors A.T. Basokur, N. Meqbel, Ö. Hacioglu, H.I. Arslan and T. EfeçinarSummaryA magnetotelluric survey has been conducted in the Cappadocia region of central Turkey in order to find new geothermal resources. The survey area has formerly been postulated as the location of a buried caldera that was one of the main eruptive centres of Cappadocian Volcanic Province. Three-dimensional non-linear conjugate gradient inversion of magnetotelluric data by using the full impedance tensor helps to delineate the subsurface resistivity distribution. The derived resistivity model reveals the possibility of a buried caldera. The low resistivity anomalies are interpreted as the clay alteration zones caused by hydrothermal activities.
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Processing and interpretation of geological and geophysical data for establishing the geothermal resources
Authors N. Asimopolos and L. AsimopolosSummaryA geothermal system can be described as a system in which water is used as a transport agent, through which the heat is taken from the sources from basement and transmitted to the consumer. The main elements of a geothermal system are a source of heat, tank and transport fluid, represented by water. The geothermal prospecting for the entire territory of Romania, carried out by temperature measurements allowed the development of geothermal maps, highlighting the temperature distribution at different depths and heat flow. For a good image of the Romania’s geothermal potential, we present, in our paper these maps, that made with the Surfer program, based on the data obtained through digitalizing geothermal maps of Romania (scale 1: 1000000) using Surfer software, kriging method for interpolation. Also, we made maps with other geophysical parameters after smoothed and filtrated of geophysical data (Bouguer anomaly, Free Air anomaly, geoid) and correlations between them.
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Investigation of Geothermal Potential of Balıkesir-Sındırgı-Düvertepe Area with Magnetotelluric Methods
Authors C. Sari, E. Icoz and E.G. YurtkalSummaryIt is aimed to investigate the potential of geothermal fluids to be used in the power plant. The purpose is to determine the total thickness of the sedimentary units and the basement topography, to clarify the underground structure, to identify the regions that can operate in terms of geothermal energy and the lateral discontinuities of the sedimentary units. The study was carried out in the eastern part of Sındırgı/Balıkesir Province (Turkey). 60 MT and AMT measurements were made in the area and the deep geological structure was tried to be clarified. Paleozoic metamorphic rocks and the Upper Cretaceous age series which are incompatible with them were found in the study area. Upper Miocene volcanics unconformably overlie the complex sequence. These units cover alluviums unconformably, especially in stream beds. According to the results, it was found that there were many lateral discontinuities in which the throws and directions were very different from each other. When the cross-sections were examined in terms of the resistivity distributions, it was observed that low resistivities, high-very high resistivities dominated deep in the regions near the surface. The low resistivity zones between very high resistivity blocks were interpreted as a possible volcanic activity in the area.
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Tentative oblique subduction high resolution models, lead to reducing costs of HPCC usage
Authors M. Pomeran, L. Zlăgnean and L. BeşuţiuSummaryThe Computational Fluid Dynamics (CFD), is a method of analysis which scientists and engineers are using to build high complexity models. One of the most important side problems of CFD is the cost of operating the computational infrastructure, that is increasing along with the models.
This work tries to contribute a technique of building high resolution CFD models along with reducing these operational costs. We try to rise the awareness to an understated part of the parallelization process: the mapping phase, when the bulk computing load is distributed towards the individual computing cores of a computing cluster.
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Wireless Mobile Digital Device for Ambient Noise Recording
Authors D.Z. Zlatanski and D. GospodinovSummaryA wireless ambient noise accelerometer (ANA) device for data recording, based on a tri-axial acceleration sensor, has been developed by us. The mobile device has wireless control allowing great mobile convenience. The device is designed to record microseismic ambient noise on the basis of which to analyze the fundamental response frequency at the recording site. It is based on the three component ADXL355z acceleration sensor, featuring a 24bit ADC. The applied method for the data analysis is the H/V spectral ratio technique. We performed simultaneous recordings of ambient noise at two sites with two systems – ANA and a velocimeter GBV-316. The obtained results are similar, which reveals the applicability of ANA for ambient noise recording and site effects analysis.
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Absolute magnetic measurements, methods, and instrumentation
Authors A. Domjan, L. Hegymegi and C. HegymegiSummaryAbsolute geomagnetic measurement is an accurate determination of magnetic declination D and inclination I at a given location and time on the Earth. These quantities are essential to monitor the long-term baseline changes and calibration parameters of variometers in observatories and repeat station surveys.
Methods and the instrumentation are tightly coupled to this kind of measurement. Since all the relevant methods based on the usage of a classical theodolite equipped with one-axis magnetometer known as declination inclination magnetometer (DIM).
DIMs have several difficulties. Measurement process is carried out manually. Difficult to use DIM for I observation in equatorial region because the microscope cannot be read in nearly vertical position even with diagonal eyepiece. The computation of magnetic meridian is calculated by the operator during the measurements.
To overcome this problem at MinGeo company we developed a cable-less, digital, non-magnetic DIM instrument, named as FluxSet Declination Inclination Digital Station (DS), which was designed to facilitate the absolute magnetic measurements.
The aim of this presentation to asses the accuracy and precision of the absolute magnetic measurements, which were measured by some reference DIMs and DS instrument using null and this new proposed method.
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High Resolution Reflectivity Inversion with Cauchy Regularization and Acoustic Impedance Conversion
By H. KarslıSummaryAcoustic impedance (AI) is one of the most effective ways of quantitatively interpreting seismic data and can simply be obtained by converting the reflectivity series of the subsurface layers. Therefore, high resolution seismic reflectivity inversion (HRRI) of the seismic data has been an important step in the seismic data processing. However, when seismic data include noise, traditional damped and undumped least square inversion methods mostly lead to unreliable and low quality results. In addition, estimation of reflectivity from seismic data is generally band-limited and negatively affects impedance producing. For this reasons, in this study, I performed the HRRI with using Cauchy regularization (HRRI-CR). The method is iteratively applied to produce reflectivity with high resolution and has anti-noise ability, which leads to obtain accurate seismic acoustic impedance results. I tested the performance of the HRRI-CR method on synthetic data in obtaining the AI and showed that the method provides more accurate information about the layers when comparing the subsurface layer model with calculated impedance curves.
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Integrated Approach for Pre-drill Pore Pressure Prediction in Data-limited Exploration Area—A Case Study from Offshore Myanmar
SummaryIn Basement-high Area, Gulf of Moattama Basin, Myanmar, the geological setting is complex. A significant change in tectonostratigraphy setting across the area leads to different sedimentation and thermal maturation of the source rock, thereby highly variable subsurface pore pressure with undetermined mechanism occurred. Even though drillability of exploration wells depends crucially on a precise pore pressure prediction, the estimation of such pressure is problematic due to the lack of primary dataset. To ensure reliability, the assessment of pre-drill pore pressure and fracture gradient illustrated herein is performed by an integrated approach. Interval velocity from broadband seismic, borehole geophysical dataset, 3-D heat-flow model, and basin history analysis were taken into account during the course of the model construction. Additionally, to handle the prediction in this complicated geology setting, comprehensive geological interpretation was included and has shown the usefulness for validating the output and quantifying the sensible range of uncertainty.
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Velocity model building — key issue for seismic migration process
By M. GrigorovaSummaryPrestack Kirchhoff Time Migration (PSTM) is probably the most used method for obtaining proper image of complex subsurface. In areas of rapid lateral and vertical velocity changes, energy is dispersed in such a way that it is very complicated to be provide desired resolution of the data. The PSTM focuses scattered energy by moving it to a proper subsurface position if accurate velocity model is provided for migration. Only when energy is properly focused, stacking improves the quality of signals and eliminates noise. Building such velocity model, can bring significant improvement of seismic data quality (both resolution and continuity) and proper spatial structural positioning. For these reasons, velocity estimation process has great influence in seismic imaging. The process of moving seismic events to their actual location of occurrence in the subsurface is strongly dependant on the velocity model, but also is greatly affected of the whole processing quality. Seismic processing is long and comprehensive process of converting seismic field data into a meaningful seismic section and involves a lot of steps of data manipulations. The result is a high quality time image of the subsurface which better matches to the real geologic structures.
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Geophone array vs single sensor field data case study in Pannonian Basin
Authors M. Vanić, A. Saprygin, S. Milojević, I. Bogatyrev and A. PolivakhoSummaryAim of the research was to examine influence of single sensor interval and application of single sensor vs geophone array on 2D seismic data quality. Seismic data were acquired at two 2D lines with different sensor configuration. Line 1 was acquired with single sensor on 25m separation between sensors and with geophone linear array. Line 2 was acquired with single sensor at 12,5m spacing from which we obtained two data sets: with 12,5m single sensor spacing and with 25m single sensor spacing. All data sets were processed in a same way, with optimal parameters for each data set. Geophone array is giving us better coherency of reflections on stack section, leading to more geological details we can interpret. With geophone array ground roll is suppressed on later times, giving us better resolution and higher dominant frequencies in deeper parts. With 12,5 m useful signal is better preserved and it’s not spatial aliased. Ground roll is more efficiently removed on 12,5 m interval then on 25 m. Recommendation for future surveys with single sensor is to further decrease interval between sensors. This will also lead to better removal of ground roll and preserve more geological information for structural and quantitative interpretation.
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Crosshole seismic tomography for the detection of abandoned underground lignite mine galleries
Authors G. Kritikakis, A. Vafidis, G. Tsilfidis and K. PapakonstantinouSummaryThis work presents the results of crosshole seismic tomography geophysical survey at selected positions along the extension of Athens subway line #2, Ilion-Anthoupolis area (Greece). This geophysical survey aimed at: 1) the detection of abandoned underground lignite mine galleries at selected positions along subway line, 2) the mapping of geological formations and possible faults at the studied sites and 3) providing information for optimal design of tunnel path. Eleven (11) seismic tomograms of 225.3m total length and 520m total depth were generated between twenty (20) boreholes. The borehole source BIS-SH was utilized to produce highly repeatable compressional (P) waves at 2 m intervals and a hydrophone streamer consisted of 12 receivers at 1 meter intervals and a 12-channel seismograph were employed for seismic wave recording. First arrivals picking and travel time tomography were performed using SeisImager2D and ReflexW, respectively. Low velocity anomalies were found at 2 seismic sections, which probably are associated with abandoned underground lignite mine galleries or intact lignite layers. Moreover, indications for an unmapped fault presence revealed and a new tunnel path was proposed in order to avoid crossing the fault zone.
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