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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
41 - 60 of 64 results
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Empirical relations converting seismic intensity to moment magnitude
Authors I. Aleksandrova, D. Solakov, S. Simeonova and P. RaykovaSummaryIntensity is a basic parameter for assessment historical seismicity - realized until the instrumental period. The relation between intensity and seismic moment magnitude allows the creation of a homogeneous catalog. The homogeneous catalog provides compatibility of the input seismological data and allow reliable estimation of the energy distribution of earthquakes - an important stage in seismological research and essential for seismic hazard assessment. In this study are analyzed 92 earthquakes with magnitude above 4.0 (M>4.0), which occurred in space window 37.0° – 45.0° N; 21.0° – 30.0° E, during the time period 1912 – 2018 and the coefficients of the linear regression MW=MW(I0/Imax) are evaluated.
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The april 2017 MS5.2 kurbneshi earthquake and its seismogenic zone
More LessSummaryOn 8 April 2017 (GMT 13:53) a moderate Ms5.2 earthquake sequence burst in the Kurbnesh-Skavica tectonic fault zone. The main shock was located 3 km in north of Kurbnesh town and 54 km NNE of Tirana city and was felt over a larger area from northen to southen Albania. The Kurbnesh-Skavica tectonic fault zone is exposed on the ground at a length of about 35 km, according to the SW-NE direction. This tectonic segment is part of Ulza-Kurbnesh-Kukes-Prizren seismogenic fault zone. For this analysis, the local and regional data concerning the epicentral locations, focal mechanisms, macroseismic data of the April 2017 earthquake were used. The focal mechanisms of the mainshocks, indicate that deformation is taken up by NE-SW trending normal faults with strike-slip elements. Analysis of this earthquake and some other recently moderate earthquakes and also of seismic activity shed light on the seismotectonics of the area and the stress field. The Kurbnesh-Skavica transversal fault zone presents a threat to the nearby urban areas.
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Frictional Strength of Faults: Evidence for Post Seismic Deformation
By A. PinarSummaryFrictional coefficient of faults is investigated using the approach described in Iio (1997) where the orientation of a fault plane relative to the maximum compression direction is related through the equation β = 1/2 arctan (1/μ), where β is the angle between the direction of the maximum compression and the fault plane orientation, and μ is coefficient of friction. The data used are the frequency distribution of azimuth and plunges of P- and T-axes of focal mechanisms. The relation between β and μ is illustrated for different types of faults. Aftershocks of 2011 Lake Van earthquake (Mw=7.2) are utilized to demonstrate the technique. Focal mechanisms for about 400 aftershocks (Mw>3.5) are retrieved showing mostly reverse and strike-slip faulting mechanisms. The frequency distribution of P-axis azimuths of the mechanisms are utilized as an approach to investigate the frictional strength of faults on and around the ruptured fault. The azimuth of predominant frequency of P-axis distribution determined separately for reverse and strike-slip focal mechanism are close to the orientation of the maximum compressive stress axis pointing out low frictional coefficients that is likely due to post-seismic deformation.
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Seismicity of the Shabla-Kaliakra-Balchik region over the period 1986–2014
Authors M. Tsekov, E. Botev, L. Dimova and R. RaykovaSummaryWe study spatial and temporal properties of the seismic activity in the Shabla-Kavarna-Balchik region over the period 1986–2014. This region is located in the NE part of Bulgaria (longitude range between 27.75E and 30.0E, and latitude range between 43.0N and 44.3N). The seismic activity there is related to a multitude of onshore and offshore faults. We use data from the Bulgarian National Seismic Network to identify 204 earthquakes in the region for the considered period. We find that the seismic activity rate increases abruptly after the August 5th 2009 Md=4.7 offshore earthquake. We identify the most active faults in the region for the considered period: (1) the Kaliakra fault; (2) the Batovo fault; (3) the Shabla fault; (4) the Razelm fault, as well as several near-coastal NNE-SSW faults where the aftershocks of the strong quake of August 2009 concentrated. The spatiotemporal behviour of the earthquake activity in the region suggests possible interaction between adjacent or intersecting regional faults.
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Extensive strike-slip faulting to NNW-part of Lake Erçek region by finite source and coulomb modeling (E-Anatolia)
More LessSummaryWe have examined the finite fault source characteristics of the October 23, 2011 Erciş-Van earthquake through modelling the seismic waveforms recorded at local and teleseismc distances. A finite source model has been retrieved using the teleseismic body waveforms constraining the source location by info given in previous studies. The finite source modeling suggests a major moment release on a transpressive fault segment located at the central part of the source region surrounded to the SW and NE by strike-slip faults acting as tear faults with the accretionary prism in Eastern Anatolia. We examine the fault interaction between the fault ruptured by the mainshock and the faults that have been activated by the mainshock. Tremendous strike-slip faulting has been observed to the NE of the source region extending in a depth range from shallow subsurface to the lower crust. A Coulomb stress modeling using the slip model derived indicates a stress increase in the lower crust on the optimally oriented strike-slip faults extending from shallow crust to deeper lower crust.
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The present geodynamics and kinematics of albanides
More LessSummaryIn the present work, an introductive summary of the Albanian geological position within the framework of the regional geology is briefly given. Additionally, the neotectonic structure of the Albanian territory is comprehensively described, analyzing the geological formations which build it up. The geological structure of Albania appears folded and complicated by various tectonic faults of different type and age.
Treatment from the regional geological standpoint is ascribed to the relationship between the Albanian orogens and the Adria microplate, as a reference tectonic unit, continuously playing an important role in the geodynamics, kinematics and tectonic modeling of the Mediterranean basin, and consequently on the Albanian territory.
Herein, results on the Albanian territory geodynamics and its relation to the Apulian block and Eurasia are discussed referring to the GPS data obtained from the Albanian GNSS and neighboring analog networks. Special attention is dedicated to the correlation of these data with the tectonic pattern of the Albanian territory. Based on the instrumental observations, the movements and the strain pattern of the external and internal Albanides, referred to the up-mentioned tectonic blocs, are correspondingly discussed.
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Azimuthal rotation-dependent spatial distributional patterns of small repeaters estimated from microseismic data-set of Gokova Gulf (SW-Turkey)
By M. TokerSummarySmall repeating earthquakes reveal properties such as the temporal and spatial clustering of events, which serve as a key tool to constrain the rate/state stress transfer and seismogenetic properties of active seismic areas. In our case, azimuthal rotation-dependent spatial patterns of the small repeaters were estimated from the four years-microseismic data set (∼10.000 events) of Gokova Gulf (GG) (SW-Turkey). The process of microseismicity taking place in Gokova Gulf in 2010–2014 was relocated in an attempt to quantify the prominent seismogeneity in the GG and to unveil properties of the associated current stress state of the GG and its projected surroundings at crustal depths. In the present study, we evaluated the 26th November 2012 Bozburun mainshock (Mw 4.4, 4.8) with its accompanying small repeating events and its accompanying multiple aftershock series; the 16th May 2013 Ula aftershock (Mw 4.6), the 25th March 2014 Bozburun aftershock (Mw 4.0), the 1th May 2014 Bodrum aftershock (Mw 4.0) with their accompanying small repeating events, symptomatically occurring in the Bozburun, Ula, and Bodrum areas of the GG by using the microseismic data set. Then, we produced azimuth-dependent, rotational and cross sectional distributional patterns of all microearthquake clusters at depth, up to ∼ 160 km.
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Unipolar Magnetic Pulses – A Manifestation of Stress Induced Impulse Modes (A Petroplasma Viewpoint)
By P. NenovskiSummaryUnipolar magnetic pulses (UMPs) are recorded prior to strong earthquakes at different points: California, Italy, Peru. Their basic characteristics are considered and analyzed. Supposed mechanism of UMPs are underground electric currents of impulse type. Laboratory experiments have evidenced the phenomenon that igneous rocks under stress/strain change conditions turn into semiconductor plasma. Stress induced (current-carrying) impulse modes of rock plasma (petroplasma) are suggested. The emerging diffusion processes inside and outside the current-carrying channel are discussed to explain the pre-seismic UMPs ⌝ their appearance, with one polarity, pulse width, etc. A possible cause of pre-seismic UMPs is proposed.
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Pre-earthquake changes of atmospheric ozone and temperature over the wide Balkan region
More LessSummaryIncreased long-wave thermal emissions is found out prior to many strong earthquakes. Within the wide Balkans, however, there are a few recent strong earthquakes (EQs), so our analysis is aimed to test the hypothesis for the pre-EQ generation of near surface thermal anomalies, for EQs with magnitude 4 or greater. 1872 events have been selected from the EMSC catalogue of earthquakes, occurred in magnetically quiet periods, during the time interval 2004–2014. The selected area for investigations covers the region with coordinates: 80–300E longitude and 350–530N latitude. Besides temperature, the near tropopause ozone and water vapour are also analysed.
Statistical analyses, based on the ANOVA F-test of variances, and the t-test of mean values, reveals that the suggested pre-EQ influence of the tectonic processes is stronger and most significant on the near tropopause ozone density. This influence is still traceable in the air temperature at 2m above the surface, and notably reduced in the soil temperature at ~3m beneath the surface. This result is suggestive that the pre-EQ anomalies in the lower stratospheric ozone density are projected on the surface temperature, due to modulation of the upper tropospheric water vapour greenhouse power.
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GMPEs used in seismic hazard assessment for Bulgaria-selection and testing in Bulgaria
Authors D.E. Solakov, S. Simeonova, P. Raykova, E. Oynakov and I. AleksandrovaSummaryGround Motion Prediction Equations-GMPEs define the values of a ground motion parameter as a function of earthquake size and the distance in terms of both expected values and their dispersion. GMPEs are essential in probabilistic seismic hazard studies, which are a key step for the evaluation of seismic risk and loss estimation for a region. In the present study, six attenuation relationships were selected for shallow and three for intermediate depth earthquakes on the base of general criteria. The Nakamura method was applied to classify the soil conditions of Bulgarian stations. The LLH and LH approaches were used for quantifying the goodness of fit of these relations to a large dataset of ground motion data from Balkan region.
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Population exposure index – an element of seismic risk assessment
Authors D. Solakov, M. Metodiev, S. Simeonova and P. TrifonovaSummaryThis paper presents assessment of one of the main elements of the seismic risk – human exposure at the territory of Bulgaria. Seismic hazard in terms of Peak Ground Acceleration map is modelled using GIS and overlaid with a model of population distribution in order to extract a population exposure index (PEI). We use as indicator the population density to allow comparison between less populated and more populated regions. Analysis is performed on a gridded network with a single element of 1×1 kilometer. Information about the population cover the period 2011–2018 using data from the last census performed in 2011 and the updated information for the towns provided by the National Statistical Institute for 2018. As a result, a classification of region is provided based on the results obtained for PEI.
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Relief resolution effect on the tsunami numerical modelling
Authors L. Dimova and R. RaykovaSummaryThe relief resolution effect on the tsunami numerical modelling was evaluated in this study. One hypothetical tsunamigenic source with earthquake magnitude 7.5 was modelled in the area of the Shabla-Kaliakra seismic zone in the northeastern Bulgarian Black Sea coast. The resolution of computational grids on which the numerical simulations were made are 50 m, 250 m and 500 m. Synthetic mareograms were calculated at a number of points near the coastline and the results obtained by different grids, were compared. The vertical water column on the coastline generated by the modelled event is evaluated, indicating that higher resolution in the finer grid leads to more realistic results. Radiation pattern of the tsunami waves has insignificant changes using relief grids with different steps. In general the extreme amplitudes of the modelled tsunami vary with different relief resolution. The phase shift in the wave trains is more significant for a specific location that causes important changes in the estimation of vertical water column on the shore at this point. Further that it is a basis of over or underestimation of the local tsunami hazard.
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Ice generated events in Perunika Glacier, recorded by LIVV station
Authors G. Georgieva, L. Dimitrova and V. GourevSummaryIn this paper we present the initial results from our study of the seismicity generated by the processes in the Perunika glacier, Livingston Island, Antarctica recorded from Bulgarian broad band seismic station LIVV and its relationship with measured GNSS displacements on the glacier surface. Seismic and GNSS data from January 2018 were used. Different types of ice-generated events were observed. About 90 events with identical waveforms, very short duration (up to 1–2 s) and clear P and S onset were localized. GNSS measurements were carried out in five points on glacier and later the velocity in cm/day was computed.
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Evaluation of geophysical methods for studying snowfields in Pirin Mountain, Bulgaria
Authors G. Georgieva, A. Kisyov, C. Tzankov, B. Chtirkova, V. Gourev and Y. IvanovSummaryThe article stages the results of surveys conducted in 2018 in the Pirin Mountain in order to evaluate geophysical methods for studying glacier thickness and structure. Two perennial snowfields are known in Pirin and the test investigations were carried out on one of them, situated in the area of Golyam Kazan. Ground penetrating radar (GPR) and 2D electrical resistivity tomography (ERT) were selected for the survey.
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Marine (Sonar and Shallowe Seismic) Investigations in Izmir Gulf-New Results
By M. SenozSummaryİzmir Gulf is an actively growing shallow marine basin controlled by active faults trending NE, NW, N–S and E–W in the West Anatolian Extensional Province. The bay is topographically divided into an E–W-trending inner bay and a NW-trending outer bay. In the bathymetric maps was the gulf according to the shoreline into three regions divided. These regions are:the eastern (inner) part, the central part (outer part) and the western part Geologicaly is the the inner bay of İzmir an asymmetric graben structure containing upper cretaceous–Palaeocene basement, an older succession of lower to upper Miocene basin fill, overlain with angular unconformity by a younger Plio–Quaternary basin fill. The older succession contain a thick, folded and coal-bearing continental volcano-sedimentary sequence. The younger succession includes the upper Pliocene–Pleistocene Görece formation and Holocene to recent alluvial fan, fan delta to shallow marine deposits.This shallowe marine deposites will be investigated today systematicaly using modern shallowe marine geophysical instruments. This investigations reveals everyday more features of the sea bottom related bathymetry (topographie,), structures on the sea bottom (geothermal site, naturell gas site, gas seeps site, mud volcanouse site, pockmark-pockmark field site and man made object site (wreck site) in the regions of İzmir bay.
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Single spectrum analysis for monthly sea level data from Varna tide gauge station
Authors A. Ivanov, I. Georgiev and N. DimitrovSummaryClimate changes and global warming are assumed for main reasons of constant sea level rise. Survey methods such as altimetric measurements are essential for determining global processes related to sea level change, but the regional and local changes are also important. In this paper regional sea level changes at tide gauge station Varna at Black sea coast is analyzed. Single spectrum analysis is carried out for monthly sea level data for period 1929–2019. The sea level trend, long term tidal constituents, amplitudes and phases are estimated. The results clearly indicates positive mean sea level trend with value of 1.2 ±0.1mm/yr.
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Digital terrain model of the seafloor of south bulgarian black sea coast
Authors T. Lambev and B. ProdanovSummaryThe paper discuss the creation of a composite seafloor digital terrain model of the south Bulgarian Black Sea coast - broad Burgas Bay from Cape Emine to Cape Maslen nos. It is a result of processing and assembling data from single beam echosounder and multibeam sonar systems derived from the Institute of Oceanology-BAS, bathymetric LiDAR data and data from digitizing water lines from marine navigational charts. Data from single beam echosounder and multibeam sonar systems were acquired during the implementation of various national and international projects of IO-BAS. Areas where no data are available were completed by manually drown isobaths built on the grounds of the surrounding terrain and circular interpolation with step of 55 meters. By combining all the data a comprehensive 3D digital terrain model of the topography of the seafloor with resolution of 1/128 arc minute or cell size of 14 meters was created. The digital terrain model allows detailed understanding of the seafloor morphology and successfully can be used in the compilation of highly accurate, navigational charts. The work is a result of the implementation of a project under the Program for supporting young scientists and PhD students at the Bulgarian Academy of Sciences.
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Is it possible to obtain reliable archaeomagnetic results from baked clays with very weak magnetism?
Authors M. Avramova-Kostadinova and P. DimitrovSummaryThe primary goal of archaeomagnetism is to accumulate information about the behaviour of the local geomagnetic field in the past using well-dated archaeological baked clay materials. Sometimes, however, these materials can possess weak magnetic properties due to an insufficient firing in the antiquity, low amount of ferro-oxides or domination of antiferromagnetic minerals. In such cases, it is not possible applying the complete set of laboratory experiments and requirements, which assure the authenticity of archaeomagnetic data.
A detailed investigation of samples with extremely weak magnetism was performed and the reliability of the obtained data is demonstrated. These results cannot be included in archaeomagnetic database as referent feature because they will not pass all the necessary quality criteria. However, the produced archaeomagnetic determinations can serve as valuable check-up of the calculated secular variation curves (when the structure studied is well archaeologically constrained) or can be used for archaeomagnetic dating.
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Applying archaeomagnetic method to identify the purpose of usage of archaeological furnaces
Authors P. Dimitrov and M. Kostadinova-AvramovaSummaryThe potential of archaeomagnetism as a reliable dating tool (absolute and relative) is beyond any doubt. Magnetism of archaeological baked clays, however, can be used for solving other archaeological problems that are not related to the site’s chronology. In some cases, the discovered archaeological structures are so fragmented and poorly preserved that it is very difficult to establish the purpose of their usage. In this study, magnetic measurements were applied to determine maximum firing temperatures for several structures found at Prehistoric Settlement Damyanitza to find out if they were used for domestic purposes or for ceramic production. The determined firing temperatures with one exception vary from 730 to 770 °C and they are very similar to these observed for Neolithic and Eneolithic ceramic fragments analyzed with thermomagnetic method. Consequently, it can be concluded that the ovens from Damyanitza were used in the past for pottery production.
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Geophysical investigation of hidden wall passages in the historical building of Hungarian Academy of Sciences
Authors G.A. Hutka, P. Nagy, Z. Prónay and E. TörösSummaryThe main building of the Hungarian Academy of Sciences is a neo-Renaissance palace built in 1865 in Budapest, situated on the eastern bank of the Danube River. In October 2018 MinGeo Ltd. was entrusted with the task of the inspection of hidden wall passages and chimneys connected to the ceremonial hall of the Academy in order to improve its ventilation. For this purpose, we used ultra-high resolution GPR inside the building; endoscope camera and cable locator in the chimneys. With this method five wall passages were found on the ground floor of the ceremonial hall and seven on its gallery, while we had an indication of a passage at 8 locations in the Museum hall on the floor above. The GPR measurements also revealed 4 so far unknown passages in the southern wall of the ceremonial hall. With the opening of the outlet of these four passages the ventilation of the hall could easily be improved. If this is not enough, there are several more passages connected to the chimneys, which also could be utilized for this purpose.
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