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8th Congress of the Balkan Geophysical Society
- Conference date: October 5-8, 2015
- Location: Chania, Greece
- Published: 05 October 2015
101 - 120 of 124 results
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How Many Iterations Are Necessary for Obtaining Proper Depth Velocity Model?
Authors M.L. Grigorova and D.H. DabovskiSummaryPrestack Kirchhoff Depth Migration (PSDM) is a robust method for obtaining proper image of complex subsurface. In areas of rapid velocity changes, energy is dispersed in such a way that conventional stacking velocities can not provide desired resolution of the data.
Building a proper velocity model for PSDM, 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 depth imaging.
Construction of a velocity model for PSDM was conducted in two phases: preparation of initial model and its updating. The initial velocity model was derived by RMS stacking velocities. A good initial model limits ambiguity and increases convergence of tomographic solutions. Therefore, an initial model plays key role in a process of migration velocity analysis for complex structures. In the case of tomographic inversion, a wrong provisional velocity distribution makes it impossible to obtain convergent results.
Usually two to five iterations of tomographic inversion are necessary to obtain the final result. Relatively small number of iterations is needed, mainly due to definition of proper velocity gradients. During iterative tomographic updates, the resolution and plausibility of the model increase and small velocity changes can be defined.
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Examples of Multiple Suppression of Land Seismic Data
Authors M.H. Toshev and D.H. DabovskiSummaryThe attenuation of multiple reflections in land seismic data has been a low priority in seismic industry. There is however no method or group of methods that work in all area. lgorithms to removal multiples have been based on two differentiating properties i.e. moveout and predictability. Radon transform seismic data into a domain where multiples and primaries are readily distinguishable and can be separated. This separation allows multiples energy to be easily removed prior to transforming the data back into T–X domain. Algorithms of radon filter relay on residual moveout to discriminate multiples from primaries. Velocities must be picked with sufficient accuracy to distinguish primary energy from slightly slower multiple energy. Radon filter is effective when primaries and multiples are co-incident at near offsets in T–X domain. A minimum moveout of 30ms from near trace to far trace is required for this algorithm to be effective on real data. The greater moveout differential increases its effectiveness.
The study shows the importance of velocity in the effectiveness of the radon filter on multiples attenuation. The radon filter has been applied on a land dataset to attenuate the multiples to get the meaningful image of the subsurface.
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Colored Inversion and Acoustic Model-based Inversion Techniques.
More LessSummaryIn this study was used Colored and Acoustic post-stack seismic inversion techniques. Five horizons from the reservoir zone were interpreted to determine geological inputs for the model. Well-log data was used to build synthetic traces which were then tied to the real seismic data. Two different inversion algorithms were applied to invert the seismic data and their results were estimate. The inverted models showed high vertical resolution, giving an excellent visualization in the area of research.
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High Resolution Diffraction Imaging of Small Scale Fractures in Shale and Carbonate Reservoirs
Authors A.M. Popovici, I. Sturzu, T.J. Moser and C. TsingasSummaryCurrent research in the field of seismic depth imaging has identified a new approach to image with super-resolution fractured zones, fault edges, small scale faults, pinch-outs, reef edges, channel edges, salt flanks, reflector unconformities, near surface scattering objects and in general any small scattering objects, by using Diffraction Imaging as a complement to the structural images produced by reflection imaging. Diffraction Imaging is the imaging of discontinuities in the earth. Diffractions are the seismic response of small elements (or diffractors) in the subsurface of the earth, such as small scale faults, fractures, near surface scattering objects and in general all objects which are small compared to the wavelength of seismic waves. We show results in different areas of the world, in fractured carbonate and unconventional shale reservoirs. Using Diffraction Imaging to identify areas with increased natural fracture density, which correlate with increased production, the reservoir engineers can design an optimal well placement program that targets the sweet spots and minimizes the total number of wells used for a prospective area.
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The Challenge of Static Corrections in High Dune Areas / Area 201 Kufra Basin, Libya
By W. ElboaishiSummaryThis study describes the processing of the 2D seismic survey acquired in the Kufra Basin, Area 201, which is situated in the Southeast of Libya. The terrain in Area 201 falls into four distinct categories, gravel plain, sand dunes, rocky ground/jebels and rolling sand. The sand dunes tend to occur in long ‘fingers’ running from the NE to the SW direction and covering approx 5–10%, which are predominantly in the centre of Area 201.
The main objective of this study is to compare and describe the techniques that were done to solve static problem within the dune areas. Three static scenario models from three different processing contractors were offered and applied on the data to compare the best solution over the dune area. First contractor applied static model with Up-hole model and Residual refraction statics, second contractor applied only Residual refraction statics, where the third contractor applied a static model comprises of Up-hole model, Residual refraction statics and Horizon base static (HBS) correction, which gives the optimum solution to solve the static issues on the seismic lines over the dune area.
A combination of the following successively three steps was applied (Up-hole model, Residual refraction statics and Horizon base static (HBS) correction). The up-hole model statics followed by the residual refraction statics lead to good results, whereas a local anomaly in some lines was still affected by statics. These anomalies, resulted from the presence of dunes, were not solved by the up-holes model and residual refraction statics properly. To correct those, the static was locally updated with a third technique; the horizon base static (HBS) correction was applied. For the lines where the HBS corrections were done, the process gave better result. The new processed test was compared to the other two processing tests and a large improvement was noticed in terms of static issues.
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Spectral Domain Local Cancellation Procedure of Harmonic Noise in Seismic Data
Authors H. Karsli and D. DondururSummaryWe describe a simple and fast filtering procedure which is locally applied in spectral domain and uses iterative trimmed and truncated mean filter method (LITTM), to cancel harmonic noise with 50 or 60Hz and its multiples caused by power line during the seismic data acquisition in land and marine. The procedure doesn’t require any reference signal or an estimate accurately the fundamental frequency of the harmonic noise, but only it should be determined the approximate frequencies of the noise on the amplitude spectra. Real land and marine data examples show that the harmonic noise is filtered well without damaging the available frequencies around the fundamental frequency and provide clean outputs for later processes. We expect this procedure may be a useful tool to recover the signal masked by power line noise in other geophysical data.
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Long Term Earthquake Prediction in Turkey
More LessSummaryIn order to estimate the recurrence intervals for large earthquakes that occurred in Turkey, this region has been separated into thirty three seismogenic sources on the basis of certain seismological criteria, and regional time and magnitude-predictable model has been applied for these sources. Considering the inter event time between successive mainshocks, the following two predictive relations were computed: log Tt = 0.37 Mmin +0.19 Mp − 0.14 log M0 + 1.39 and Mf = 0.72 Mmin − 0.01 Mp +0.31 log M0 − 5.44. Multiple correlation coefficient and standard deviation have been computed as 0.69 and 0.30 for the first relation and 0.63 and 0.43 for the second relation, respectively. On the basis of these relations and using the occurrence time and magnitude of the last mainshocks in each seismogenic source, the probabilities of occurrence P (∆t) of the next strong and large mainshocks during the next five decades and the magnitude of the expected mainshocks were determined.
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Basic Aspects of Albanian Seismic Activity during 2014
By R. OrmeniSummaryThe main cause of Albanian seismicity is the collision of Adria microplate with the Albanian orogeny. Seismic phases recorded by the Albanian network, integrated with data of Thessalonicy (Greece), Montenegro and INGV (Italy) networks, are used to prepare the database. We present here the results of the analysis in parameters of events and some features of seismicity that have occurred in the Albania and its surrounding area during 2014. The earthquake foci are concentrated mostly along the some active faults. In the Fieri-Elbasani-Dibra occurred a moderate earthquake (ML = 5.2 Richter). This transversal fault zone belongs to a complex faulting environment. In the vicinity of Fieri was registered a small series of earthquakes that supposed to be an inducted seismicity.
Thr Durres- Gjiri i Lazlit -Ulqini fault zone is located near the Albanian orogen front, in convergence with Adria micro plate, and for this reason compress movements here are strongest ones. Increased seismic activity was registered nearby of southern Albania on the Greece territory and in easthern Albania on Macedonia territory.
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Application of Finite Elements Method in Space for Deformation Analysis of the Territory of Bulgaria
Authors K. Vassileva and G. ValevSummaryThe paper presents a study of the earth crust movements for the territory of Bulgaria by applying the Finite Elements Method on the base of results from GPS data processing. The theoretical base of the developed by the authors FEM for the space is presented shortly. As an appropriate method for deformation analysis of large territories the proposed finite elements model is applied for the territory of Bulgaria using estimated Cartesian coordinates of BULiPOS GNSS network stations. One week GPS data from each of the five years 2009 – 2013 of BULiPOS network stations have been processed with Bernese software, version 5.0. The estimated Cartesian coordinates of the stations have been transformed into the system ETRF2000. These relative to the Eurasia stable plate station coordinates have been used in the finite elements model. On the base of the obtained results several areas of compressions and extensions could be distinguished but not quite clear. Generally it can be suggested that deformations in part of central, central-east and south-east Bulgaria are of compression, in north-west, south-west and in part of central Bulgaria —of extension. More stations over the territory of the country will contribute to better clarification of deformation processes.
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P Wave Tomography of the Western Mediterranean Region and the Gulf of Cadiz. Constraints on Regional Geodynamic Models
By M.N. BeghoulSummarySelected Pn arrival times extracted from the ISC data, covering the time period from 1964 to present, are used in a non classical tomography scheme, to map with an improved resolution, the lateral velocity variations of the mantle lid in the Western Mediterranean region and the Gulf of Cadiz. This tomography reveals that all the recent shallow large instrumental earthquakes (Mag ≥ 6.5) in the Maghreb region and in the Gulf of Cadiz, have all occurred in areas where (a) the mantle lid is cold with velocities larger than 7.95 km/sec, (b) significant lateral mantle lid velocity variations occur around these areas, in particular in the region where has occurred the 1755 Lisbon earthquake (Mag = 8.5–9.0). A vey hot mantle lid is observed in the Alboran Sea; consistent with a delamination of the westward underthrusted oceanic plate in the Gulf of Cadiz; whose cold shadow edge, is well outlined by the tomography. The thermal effect associated to the Calabrian Arc wedge, extends westward in the Mediterranean sea, on wavelength of at least 700 km. It contributes to warm the continental lithosphere of the northern edge of the eastern part of the Tellian Atlas, preventing it to nucleate large earthquakes.
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Source Effects of Vrancea Earthquakes vs. Site Effects Recorded in Bucharest City, Romania
More LessSummaryDifferent studies focused on the Vrancea subcrustal source of earthquakes pointed out the strong lateral inhomogeneous distribution of the seismic radiation. This implies characteristic macroseismic distributions, extremely elongated along NE-SW direction, and sharply restraint toward NW and SE. The fault plane solutions of most Vrancea earthquakes indicate a nearly pure thrust mechanism with the B-axis striking NE, which is typical for the strongest events. We analyze the influence of focal mechanism radiation on the ground motion parameters in Bucharest area.
The analysis of a recent set of intermediate depth earthquakes with Mw > 4.5, for which the focal mechanism have been computed, show the significant role played by the variation of these parameters in respect to the seismic motion recorded. These parameters might be as important as the site effects in establishing the local seismic hazard for the Bucharest City.
The role of the focal mechanism of the earthquakes and of the depth at which the earthquakes occur determine the path on which seismic waves are propagating to the surface. A significant role is played by the variation of the lithosphere structure between the depth of earthquakes and the surface, for the seismic motion recorded in the Bucharest area.
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Initial Stage of the Project for Research Seismicity of Livingston Island
Authors L. Dimitrova, G. Georgieva, R. Raykova, V. Gurev, P. Raykova, V. Protopopova and M. PopovaSummaryThe paper presents the assessment of the hardware and software equipment as the initial stage of the implementation of the project DFNI I02/11 “Creating an information base for exploration of seismicity and Earth structure of Livingston Island and surroundings by complex research in the Bulgarian Antarctic Base area”. Broad Band seismometer Guralp CMG40T with flat frequency response from 30s to 50Hz and digitizer Reftek DAS130 were installed in the yard of Vitosha Geophysics Observatory (1400m). The equipment was working in extreme weather conditions during February, 2015. The distribution of Power Spectral Density of the ambient noise was estimated and the performance of the tested equipment and the seismological equipment working in the Observatory was compared. Software developed on the base of Golitzynin method and the receiver function techniques were applied over several earthquakes. The assessment of the efficiency of the hardware equipment and the methods applied proved that they are suitable to explore the seismicity of Livingston Island and surroundings.
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A Study of the 2012 Mw5.6 Earthquake Aftershock Sequence
Authors D. Solakov, S. Simeonova, P. Raykova, V. Protopopova, I. Aleksandrova and M. PopovaSummaryAn earthquake of moment magnitude 5.6 hit Sofia seismic zone, on May 22nd, 2012. The earthquake occurred in the central part of western Bulgaria at about 25 km south - west of the city of Sofia (the capital of Bulgaria). It is worth mentioning that the May 2012 Mw5.6 earthquake occurred in the area characterized by a long quiescence (of about 95 years) for moderate events. The results favor the idea that neotectonics of the central-western Bulgaria is similar to that of northern Greece with predominant N-S extension.
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Fluctuations in Plates-coupling Strength Suggested by Episodic Triggering of Shallow Earthquakes at the Carpathians Bend
Authors H. Mitrofan, M.A. Anghelache, M. Visan and F. ChiteaSummaryThere has been analyzed the 1965–2015 time-series of shallow (<60 km) earthquakes recorded next to the SE Carpathians bend, at the contact between the Moesian and East-European tectonic plates. It seems that each of the major (Mw 6.9) Vrancea earthquakes having occurred nearby, at intermediate-depths (>60 km), during the 1977–1990 time interval, succeeded to trigger a subsequent enhancement of that shallow seismicity: presumably, by episodically unblocking channels along which high-pressure/ultra-high-pressure rocks were ascending, in a discontinuous process of exhumation, by the present time. Yet even in periods when only moderate shocks (Mw<6) occurred at intermediate-depth in Vrancea region, focal mechanisms of shallow earthquakes, as well as vertical GPS displacements, were still consistent with an ongoing up-flow of exhuming material; consequently, by taking into account that no waves generated by a strong earthquake could have been then involved in unblocking exhumation channels, it was suggested that in those periods, the exhuming material ascent should have proceeded more unrestricted. Overall considered, since the hypothesized exhuming pathways presumably followed the contacts between the tectonic plates which are juxtaposed in that region, such distinctions noticed in terms of shallow earthquakes generation could be related to the strength of the coupling between the involved plates.
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Mapping b-Value in the Seismogenic Zones of Albania Region
By R. OrmeniSummaryWe map the b value of the frequency magnitude relationship of earthquakes in map views in the seismogenic zones of the Albania from the corrected and declustered background seismicity catalogue based on Md scale, covering the time period between 2001 and 2014. The computed spatial distribution shows strong spatial heterogeneity within the range 0.84±0.04 and 1.33.±0.049 in the seismogenices zones. Anomalously low b-value areas more or less coincide with the spatial distribution of M≥5.0 earthquakes and their known rupture extents. A clear decrease in temporal distribution of b-value is observed before the moderate main shocks. In generally the spatial distributions of b-value reflect the known seismotectonic structures of Albania. Mapping of the b-values provides detailed images of the zones presenting low and high seismic activity and it may be used as a measure of seismic potential sources and relative hazard levels.
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Physically Based Ground Motion Simulation Methodology and Validation with Mid-Sized Marmara Sea Earthquakes
Authors A.M. Mert, Y.F. Fahjan and L.H. HutchingsSummaryIn this paper we have two main purposes. The first one is to simulate midsize earthquake recorded in the Marmara region. The region has a geologically complex and heterogeneous crustal structure and we therefore utilize EGF to constrain high frequency wave propagation. We synthesize ground motion for the full wave train on three components, and applied a ‘physics based’ solution of earthquake rupture. The simulation methodology is based on the studies by Hutchings and Wu (1990) , Hutchings (1991 , 1994 ). We synthesized seismograms using by 500 different rupture scenarios that were generated by Monte Carlo selection of parameters within a range.
The second purpose is to validate synthetic seismogram with real seismogram. To develop credibility of synthetic seismogram in engineering point of view, we follow the methodology presented by Anderson (2003) . This methodology proposes a similarity score based on averages of the quality of fit measuring ground motion characteristics and uses a suite of measurements.
Because the methodology produces source and site specific synthetic ground motion time histories and goodness-of-fit scores is ‘excellent’ based on Anderson’s score, we concluded that it can be used to produce ground motion to develop or improve seismic codes and standards.
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Recognition and Restoration of Shelf in the Bay of Vlora
Authors M. Bonjako, S. Bonjako and S. DhimaSummaryMain objectives: Studying the spread of Quaternary deposits in the region of the Bay of Vlora, which are located in the southeast of Albania, and in the south of Pre Adriatic Depression, is of interest not only because of their thickness, which rise from the sea coast towards its depth, but also for the nature of their spread and formation.
Quaternary deposits in the Bay of Vlora region are represented by marine sediments of Pleistocene and continental Holocene. Seismic profiles carried out in the region, on land and at sea, provide data on their spread. Through the ecological study of micro fauna, such as foraminifera dominated by Ammonia beccarii and Ammonia tepida, and associations with ostracoda dominated by the representatives of Cyprideis genus, found in these deposits, was determined the existence of interior shelf during the Quaternary, which was separated by the exterior shelf of that time in the Bay of Vlora by the Serravallian surface deposits in Zvërnec, which have served as a barrier
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The Tectonic Style of Carbonates in the Kurvelesi Structures Belt according to Seismic Data
Authors K. Jano, I. Gjermani and M. SinaSummaryGeographically, the region treated in this article is located in the south - western Albania and belongs to the Ionian Tectonic zone, located in the western part of the External Albanides. From the tectonics point of view the Kurveleshi Belt structures is included in the central part of the Ionian Tectonic zone and it is characterized by a developed tectonic activity and the presence of continuously generating and storing hydrocarbon rocks in the Mesozoic carbonate section. The interpretation of seismic data and usage of the correct layers velocities, in this tectonic region associated with considerable overthrusts have helped much in the identification of the geological model in order to identify new structures for petroleum exploration. In this article it is shown the interpretation of geological and geophysical data for anticline carbonate oil structures Selenice - Gorisht - Kocul - Amonice related to prospective exploration towards the south.
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Earth Crust Movements of the Territory of Bulgaria and North Greece from the Results of New GPS Data Processing
Authors K. Vassileva and M. AtanasovaSummaryThe work presents a study of the earth crust movements for the territory of Bulgaria and north Greece on the base of new processing of GPS data from 36 GNSS permanent stations on the territory of study. One week data from each year are used from all four years 2011–2014. The estimated station coordinates and station velocity components in system ITRF2008 are transformed in the system ETRF2000 to be obtained the local movements of the stations as more representative of their behaviour. Combinations of the obtained relative velocity vectors of different stations are used for estimation of different relative Euler poles and rotations. Estimated Euler parameters are analyzed to be defined potential microplates of the study territory. The results confirm the motion of Moesia platform in direction and magnitude, determined by other researchers as well. A clear transition boundary between the Moesia platform and the southern Bulgaria zone is not found but it is found a counterclockwise rotation of the central-south part of the Maritsa zone. The behaviour of the stations of north-west and north-central Greece confirm the suggestion that they belongs to the Aegean extensional zone.
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Determination of Earthquake Hazard Parameters Using Different Eartquakes Catalogues in İzmir, Turkey
More LessSummaryThis study aims to determination of earthquake hazard parameters, such as mean activity rate λ, b value of the Gutenberg-Richter relationship and maximum regional magnitude Mmax, of İzmir city and its surroundings (26.00º–29.00º E, 37.00º–39.00ºN). For this purpose, the data obtained from international databases (i.e., International Seismological Centre, ISC and National Earthquake Information Centre, NEIC) and a national database (i.e., Kandilli Observatory and Earthquake Research Institute, KOERI) were used. The b-value in the Gutenberg-Richter relationship was calculated using two classical equations (i.e., Least Squares Method, Maximum Likelihood Method) and a new equation (i.e., Kaltek Method). The values of Mmax were obtained by Tate-Pisarenko and Kijko-Sellevoll (Cramer) methods. According the results average of b=0.74 and Mmax= 6.48 value were determined as.
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