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11th Congress of the Balkan Geophysical Society
- Conference date: October 10-14, 2021
- Location: Online
- Published: 10 October 2021
1 - 20 of 86 results
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Geotechnical Investigations in Lignite Open pit Mine Using Electrical Tomography (2D&3D) and Seismic Reflection Methods
Authors N. Andronikidis, G. Kritikakis, A. Vafidis, H. Hamdan, Z. Agioutantis, C. Steiakakis and N. EconomouSummaryThe application of seismic reflection and electrical resistivity methods (2D and 3D) in geotechnical investigations is explored through a case study in Northern Greece. These methods were employed to Mavropigi lignite open pit mine and the surveyed area is the next step in mining expansion. The main aim of the geophysical survey was to map the bedrock, the contact between the Neogene and Schist/Carbonate formations as well as to estimate the thickness of the carbonate rocks on top of the Schist formations in order to study the stability of the final mine slopes. These geophysical data provides a geotechnical model which will be used in mine planning from Greek Public Power Corporation.
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Multidisciplinary Approach for Fluvial Architecture Modelling and Reservoir Properties Estimation
Authors G. Georgieva and A. KisyovSummaryA multidisciplinary study conducted as practical training for students is presented. It combines detailed lithofacial profiling and 2D mapping of the surface outcrop. In addition to the classical geological methods that were represented, the possibilities of different geophysical methods (2D electrical resistivity, seismic, seismology (H/V spectral ratio), gravimetry, magnetometry, georadar, and aero photogrammetry) were also demonstrated in the study. Based on the conducted geophysical and geological measurements main sedimentary sequences were delineated and an attempt was made to track them spatially within the studied area.
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Use of Magnetic Susceptibility, Sedimentary, Geochemical and Mineralogical Determinations, in Research on Danube Delta Paleogeographic Changes
Authors I. Stanciu, R.G. Dimitriu, I. Stănescu, M. Barbu, D. Vasiliu, C. Gheablău and I. PojarSummaryThe data presented in this paper are the result of field and laboratory investigations carried out south of Sulina branch of Danube, close to its discharge into the Black Sea at Sulina city (Romania), as part of a multidisciplinary study on paleogeographic changes in the Danube delta, and the Romanian Black Sea coastal area. The results are presented in the form of a W-E longitudinal cross section built on detailed litho-stratigraphic columns of cores extracted from three boreholes (3 - 5 m deep) drilled in 2019 by a GeoEcoMar research team, correlated with volume magnetic susceptibility measurements and interpreted based on geochemical and mineralogical determinations.
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Evaluation of the Landslide Hazard and Risk Assessment Using GIS and Remote Sensing –Dambovita County
Authors M. Gheorghe, I. Voda-Marc and F. ChiteaSummaryWe focused our research on a north part of the central region of Dambovita County, part of the relief unit known as Subcarpathians of Ialomiţa as severe events of the mass movement were reported during time, but have never been the subject of a detailed investigation with modern techniques.
According to the GIS-based risk analysis, the areas that are most prone to landslides are found in the eastern and south-eastern parts of the study area, in the Mercani and Baloiu Hills, where steep slopes are predominant and geology includes schist, flysch, and sandstones.
However, the landslide susceptibility model is theoretical, being an approximate prediction of the real dynamic of the actual situation in the study area, given in terms of probability. On the other side, InSAR techniques depict the real past and present dynamics of the surface, by measuring surface displacement. These two techniques can be cross-correlated in a future study for validating the results of the susceptibility model.
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Applying the DInSAR Method for Surface Deformations Detection in Pernik Valley
Authors M. Atanasova-Zlatareva and H. NikolovSummaryThe need for regular monitoring of the ongoing surface displacements is highly recognized by local, national, and international authorities since they are responsible for losses of human lives and cause significant damages to homes, infrastructure, and industrial objects. In this research, the DInSAR method was applied to investigate the ground deformations in a highly populated and industrialized area of the Pernik valley. Outlined in it are the advantages of the technique used and the possibilities offered by processing freely available SAR data to produce reliable results concerning the Earth’s motions in the researched area.
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Gpr Data Migration Velocity Estimation Using a Local Diffraction Multi-focusing Criterion
Authors N. Economou, J. Brintakis, N. Andronikidis, G. Kritikakis, E. Kokkinou, N. Papadopoulos, N. Kourgialas and A. VafidisSummaryWe use constant velocity migration of Ground Penetrating Radar (GPR) sections over a predefined range of migration velocities for the validation of diffraction focusing, using local slopes distribution, with the scope to estimate a migration velocity model. We avoid the user dependent diffraction analysis to circumvent subjectivity and use overlapping x-t windows to retrieve diffraction focusing validation for the entire dataset. The estimated migration velocity is utilized as an attribute whose sensitivity in water variation saturation is tested as a complementary method to the Electrical Resistivity Tomography (ERT) method for the assessment of soil moisture.
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GNSS and InSAR Monitoring of Landslides and Troposphere in Bulgaria: State-of-the-art
Authors K. Vassileva and G. GuerovaSummaryHigh precision Global Navigation Satellite System (GNSS) and Synthetic Aperture Radar Interferometry (InSAR) are widely used today for various applications ranging from ground deformation to weather prediction. For both InSAR and GNSS products require correction of the atmospheric disturbances. In this work, a brief review of the state-of-the-art of both techniques and their application for monitoring of landslides and troposphere in Bulgaria is presented and future synergy is discussed. In particular, exploiting the combined GNSS and InSAR tropospheric products for severe weather monitoring.
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Application of ert in the Study of Debris-flow Source Area: Case Study Selanac Debris Flow
Authors D. Đurić, J. Krušić and B. AbolmasovSummaryDuring the extreme and extensive rainfall period in Serbia during May 2014, the western part of Serbia was the most affected area with landslides, flash floods, etc. In a period of 72 hours, a maximum of 200mm rainfall was recorded in the Loznica region. As a consequence, numerous landslides and floods occurred within the area. The largest debris flow ever observed in Serbia, named Selanac, was among them. This work aims to investigate whether is the upper part of the Selanac debris flow conditionally stable area by applying the 2D ERT technique.
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Some new Insights on the Correlation of Isoseismal Maps With Terrestrial and Satellite Gravity Data
Authors S. Dilalos and J.D. AlexopoulosSummaryBased on the results of a previous terrestrial gravity survey that was carried out in Athens basin (Greece) some indications of correlation between terrestrial gravity data and isoseismal maps of Athens earthquake (7/9/1999) had been revealed. In this paper, we will present a research for the same area based on a new approach, which investigates the possible correlation of the same isoseismal maps with only satellite gravity data from GOCE and GRACE but also with a combined gravity model of updated terrestrial, marine and satellite data. The combined gravity model of Greece was constructed based on the least-squares collocation.
The previous correlation of isoseismal maps with the older terrestrial gravity data was quite obvious and clear since the areas with the lower gravity values were simultaneously the ones with the greatest damage distribution. On the other hand, from the satellite gravity data and the combined gravity model we could not identify a clear and obvious correlation, as was expected, due to the smaller resolution spacing of the satellite data.
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3D Modeling of Water-saturated Layers by Using the HVSR Method of Poisson
Authors E. Oynakov, D. Solakov, I. Aleksandrova, M. Popova and D. DragomirovSummaryWaters under Earth’s surface are difficult for direct observation, and so the monitoring, mapping and modeling are needed to determine the presence of subsurface waters. Usually, the geoelectrical method is used to determine the presence of underground waters. The present study shows that the HVSR method can be used in the research of underground waters.
The present study is aimed at researching the underground aquifer and the local geology of a landfill which spreads under three institutes of the Bulgarian Academy of Sciences (Institute of information and communication technologies, National institute of geophysics, geodesy and geography and Institute of Mechanics) with the use of HVSR method (Horizontal to Vertical Spectral Ratio).
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Earthquake Scenario for the City of Veliko Tarnovo
Authors D. Solakov, S. Simeonova and P. RaykovaSummaryEarthquakes adversely affect large parts of the Earth. Global seismic risk and vulnerability to earthquakes are increasing steadily as urbanization and development occupy more areas that a prone to the effects of strong earthquakes.
The territory of Bulgaria represents a typical example of a high seismic risk area in the eastern part of the Balkan Peninsula. Over the centuries, Bulgaria has experienced strong earthquakes. Some of Europe`s strongest earthquakes in the 20th century occurred in the territory of Bulgaria.
The present study is a comprehensive earthquake scenario study. A deterministic earthquake scenario for the city of Veliko Tarnovo is generated. The study is guided by the perception that usable and realistic ground motion maps have to be produced for urban area. The local ground shaking levels are computed using six ground motion prediction equations (GMPE’s). The scenario maps account for soil amplification effects using the geotechnical zonation of the considered urban area. The results show that macroseismic intensity varies between 8.3 and 8.6 MSK, the peak ground acceleration and velocity vary between 0.30 and 0.37 g, and 26.9 and 38.5 cm/s, respectively.
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Geomagnetic Events Recorded in PAG Observatory During the First Year of Solar Cycle 25
Authors M. Metodiev and P. TrifonovaSummaryGeomagnetic observatories placed all over the globe determine some parameters which show the geomagnetic activity as a signature of the response of the Earth magnetosphere and ionosphere to solar forcing. Indices might be local, which are calculated from data of a single geomagnetic observatory, or planetary, which characterize the planetary disturbances of the geomagnetic field as a whole. We use the (local) K-index which is a 3-hour quasilogarithmic scale developed to measure magnetic activity ranging from 0 to 9, with 0 indicating completely quiet conditions and 9, representing extreme magnetic activity. The Solar Cycle24 finished in December 2019 and started the Solar Cycle 25. There are prediction that SC25 will be similar in size to SC24 with a maximum expected to be in 2025. A different hypothesis is also published suggesting that SC25 could be among the strongest sunspot cycles ever observed. We examine the geomagnetic activity events during the first year of the new cycle. Our data show that 2020 had calm geomagnetic conditions. Only 12 days have reached the levels of a minor storm in the records of PAG observatory. Two autumn periods are chosen to display the local geomagnetic response of the observed solar impacts.
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Importance of Using a Reference Base Station in Geomagnetic Surveys - Case Studies from Bulgaria
Authors P. Trifonova, C. Tzankov and M. MetodievSummaryDuring ground magnetic surveys are recorded signals from a wide variety of sources – from terrain, natural and man-made surface features, as well as instrumental, geological, and planetary sources. Such signals directly disturb the subsurface effects over the Earth’s surface causing errors in the measurements. External variations which are due to the Solar-Earth interaction are one of the “noise” signals which are always removed as a preprocessing procedure. This could be done by using a locally installed base station or using the data from the nearest geomagnetic observatory.
We analyze records from six ground surveys accomplished on the territory of Bulgaria using a reference base station to see what would be the errors if such station was not available and Panagjurishte observatory data were used instead. Our results show that the differences in the recorded daily variations are limited to ± 5 nT and the frequency interval is large enough to prevent the misinterpretation of signals from the real sources.
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Izmir and Uzunada Faults (Chirp Profiles)
By M. SenozSummaryTurkey is expressed between Arabian and Eurasian plates and this pressure cause extension towards westward and this movement creates an N-S extension regime. As a result, we observe active faults at a range in scales in different directions in the extensional tectonic regime at the Aegean region, western Turkey. The Gulf of Izmir is located in this tectonic region. Recently, high-resolution reflection seismic data were acquired and processed in the region. Data interpretation gives detailed information about various faults and complex morphology of the Izmir Gulf region. Multibeam echosounder and CHIRP seismic data enable the identification of offshore faults. In the southern offshore only E-W directional normal fault (Izmir Fault) is observable. In the west of the Gulf of Izmir, SE-NW directional - Uzunada Fault is observable. Uzunada Fault splits into many segments, controlled by the tear fault. An active graben in the Gulf was observed parallel to the Uzunada Fault Zone. Seismic data showing that tectonic activity in Uzunada Fault Zone has a great influence on the deformation of the sea bottom of the inner, central, and outer Gulf of Izmir. New seismic data enable to the identification of another offshore fault named Foça-Suzbeyli Fault.
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The Serie of Korca Earthquakes 2019 to 2020 (Mmax=5.3) and its Seismogenic Zone
Authors R. Ormëni, N. Frasheri, I. Hoxha, A. Berberi and E. SilloSummaryA series of earthquakes of maximal magnitude (Mmax=5.3) started on June 01, 2019, at 04:26 (UTC), in Flloq village about 15 km southwest of Korca town, epicenter coordinates 40.47°N dhe 20.71°E and the focal depth 14 km. This earthquake expresses the increased seismic activity of the Korca-Erseka seismogenic zone. We present results from an analysis of local and regional data concerning epicenter location, focal mechanism of main shock, and its aftershock activity. Composite focal mechanism of the main shock according to GFZ shows a normal fault: Strike=216°, Dip=52°, and Rake (Slip)= -90°. The larger aftershocks occurred southeastern of the main shock epicenter. In this fault zone were located 947 earthquakes with ranging magnitude 0.6 to 5.3 Richter with an average depth of 11km and maximum depth of 63 km. The main shock was generated by the activation of a NNEStriking normal fault. The region affected by this series of earthquakes together with the strongest earthquake of May 1960, forms a roughly NNE trending active seismotectonic zone in southeastern Albania presents a threat to nearby urban areas in Albania.
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Evaluation of Macroseismic Field of June 1, 2019, Korca Earthquake in Albania
Authors R. Ormëni, A. Berberi, N. Frasheri and O. GjuziSummaryA macroseismic investigation of a moderate earthquake with ML=5.3 at the depth of 14 km occurred on June 1st, 2019 near Floq village about 13 km S-SW of Korça town were carried out. Macroseismic investigation based on online web survey, the degree of damage to structures of human origin. The macroseismic data has been collected through the Institute of Geosciences, Energy, Water and Environment web and Emsc-csem web. This moderate shock was felt throughout southern and middle Albania, in neighboring countries, Greece and North-Macedonia, and in the epicentral area, EMS intensity reached VII-VIII degree. The maximum reported damage was in villages in the epicentral area of Korca district. Statistical analysis was applied to the macroseismic data collected in order to investigate the spatial distribution of intensity of the main-shock. Drawing of the isoseismic map consist of the geographical distribution of intensities averaged value for each town or village. The intensity map indicates areas of amplification and de-amplification of earthquake intensity. This paper gives an assessment of intensity, of attenuation function for the intensity of this earthquakes and intensity isoseismal map.
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Experimental Evaluation of the Dynamical Parameters f0 and A0 Using the Method HVSR
Authors M. Popova, E. Oynakov, D. Solakov, I. Aleksandrova, D. Dragomirov and R. IvanovSummaryMicrozonation is one of the main tasks in the analysis of the seismic hazard, seismic risk and the following political planning to lower damage from earthquakes. For the purposes of microzonation first the dynamical capabilities of the soil have to be determined. This information can be attained by invasive and time-consuming methods. Extra problems arise in a city area where the measurements are affected by industrial noise and traffic. It is necessary the development of quick, effective and non-invasive methods aimed at the evaluation of the seismic characteristic of the upper layers of Earth`s crust. Passive seismic methods depend on the registration and analysis of microseismic noise from a natural, as well as from anthropogenic origin, the latter being very common in cities.
In this research for the purpose of evaluating the resonance effects by seismic waves is used the method of Horizontal to Vertical Spectral Ratio (HVSR) of microseismic noise, which can evaluate the relation between soil/construction. For areas with potentially high seismic risk, like the one that is observed in the area of Sofia, this method is suitable. This method is suitable for a city area because it does not need sources of artificial origin.
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Magnetotelluric Studies and Regional Seismic Activity in the Central Part of Balkans
Authors B. Srebrov, I. Logvinov and E. BotevSummaryThe geomagnetic transfer function for periods of variations duration from 5 to 8000 seconds and some quasi-1, 2 and 3D magnetotelluric inverse modeling has been calculated. For these calculations the data for the components of the magnetotelluric field vector, obtained both in the Bulgarian geomagnetic observatories Panagyurishte (PAG) & Plana (PLN) and during the magnetotelluric field survey on the entire territory, have been used. The transfer function over a long period of time and the results of the various kind of inverse modeling have been compared with the regional seismic activity and a correlation has been found between them. This shows that the geomagnetic transfer function could be used to predict the regional seismic activity in the central part of the Balkans.
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Ecological Problems in Forest Funds of Vitosha Mountain
Authors P. Ivanova-Radovanova and G. BelevSummaryRecently climate change and active anthropogenic activity in the region of Vitosha Mountain have generated serious environmental problems in the forest fund. The increase of temperatures within territory of the Sofia Valley caused by several reasons, such as global warming, the active recreational activity of the inhabitants of Sofia and the rapid construction at the Vitosha foothills cause a significant reduction of the areas of natural vegetation. Based on the analysis of climatic data and processing of satellite images, the reduction of the size of the natural habitats of important plant communities had been observed. As an important indicator, the results of the analysis of the moisture index and the normalized vegetation index (NDVI) are used for the purposes of the study, based on data from Sentinel Hub. The analyzes show an critique decrease in the forest fund in the respect of the role and importance of the mountain as an ecological “island” within the territory of Sofia valley.
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Refraction Correction for Connection of the National Leveling Network First Order to Tide Gauge Station Varna
Authors N. Dimitrov, P. Danchev and I. GeorgievSummaryThe paper outlines some problems when applying refraction correction in order to reduce the effect of vertical atmospheric refraction in precise leveling observation. An example for calculating the refraction correction for a leveling line that connects the National Leveling Network first order to tide gauge station Varna is given. The estimation is using the model described in new Instruction № RD-02-20-1 of 15 January 2021 for the Establishment and Maintenance of the National Leveling Network. The results show that that the refraction correction is commensurable with correction for rod scale and must be applied for each set-up, appropriate weather conditions when the air temperature changed slightly throughout the day is better to be chosen. The applying of the refraction correction does not eliminate the requirements related with the maximum length of sight, minimum high of sight, balancing of the length of sights, and the choice of appropriate weather conditions.
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