The study presents and solves the 2-D elastodynamic model for seismic in-plane wave propagation i... more The study presents and solves the 2-D elastodynamic model for seismic in-plane wave propagation in laterally inhomogeneous geological profiles imbedded in a vertically inhomogeneous half-space in which an earthquake source is buried. To this end, an efficient hybrid modal summation-boundary integral equation method (MSM-BIEM) is developed and applied. The MSM is used as a tool for simulating wave propagation from the source position to the multilayered laterally inhomogeneous geological profile where the BIEM is applied. The proposed model and the hybrid tool are used to investigate the phenomena of site effects. In fact, such a methodology has the potential to investigate the combined effects of different physical phenomena like surface topography, lateral inhomogeneity and the existence of water saturation in soils on the estimation of site effects. The model and hybrid computational tool developed are applied to contribute to the seismic risk analysis of the Bulgarian capital Sofia.
A study of the site effects and the microzonation of Sofia region, based on the modeling of seism... more A study of the site effects and the microzonation of Sofia region, based on the modeling of seismic ground motion along three cross sections were carried out. Realistic synthetic strong motion waveforms have been computed for an earthquake scenario applying a hybrid modeling method, based on the modal summation technique, finite differences scheme and neural modeling. Realistic synthetic seismic signals have been generated for all sites of interest. Two groups of experiments have been performed, where in first group the ground motion is modeled for one-dimensional layered anelastic media, applying an algorithm based on the modal summation method. In second group of experiments the ground motion is modeled for two-dimensional laterally heterogeneous media and with implementation of neural network, learned and trained with real earthquake seismic records. The aim of suggested deterministic modeling is to provide site response estimates at Sofia due to the chosen earthquake scenarios a...
The intermediate-depth earthquakes in Vrancea (Romania) are particularly notable in the group of ... more The intermediate-depth earthquakes in Vrancea (Romania) are particularly notable in the group of the European earthquakes. The scope of this work is to study the seismic effects of the Vrancea seismogenic zone in NE Bulgaria, with particular attention to the towns of Russe, Varna, Sofia capital.This study is limited to the question about the level of the ground motions at North East Bulgaria in terms of recorded spectral amplitudes during the 1986 and 1990 Vrancea strong earthquakes. For this purpose we discuses: (1) a schematic geological-geotechnical outline; (2) the strong ground motion records in NE Bulgaria, due to Vrancea strong earthquakes; (3) the description of the regional seismicity and a review of the available recurrence and attenuation relationships; (4) the results from the strong motion records analysis. The results of this study confirm the significant influence of the Vrancea intermediate-depth seismogenic zone on the sites of Russe, Varna, Sofia and vicinity and t...
NATO Science for Peace and Security Series C: Environmental Security, 2009
The study presents and solves the 2-D elastodynamic model for seismic in-plane wave propagation i... more The study presents and solves the 2-D elastodynamic model for seismic in-plane wave propagation in laterally inhomogeneous geological profiles imbedded in a vertically inhomogeneous half-space in which an earthquake source is buried. To this end, an efficient hybrid modal summation-boundary integral equation method (MSM-BIEM) is developed and applied. The MSM is used as a tool for simulating wave propagation from the source position to the multilayered laterally inhomogeneous geological profile where the BIEM is applied. The proposed model and the hybrid tool are used to investigate the phenomena of site effects. In fact, such a methodology has the potential to investigate the combined effects of different physical phenomena like surface topography, lateral inhomogeneity and the existence of water saturation in soils on the estimation of site effects. The model and hybrid computational tool developed are applied to contribute to the seismic risk analysis of the Bulgarian capital Sofia.
NATO Science for Peace and Security Series C: Environmental Security, 2009
The earthquake record and the code for designing and constructing buildings in seismic regions in... more The earthquake record and the code for designing and constructing buildings in seismic regions in Bulgaria have shown that the country is exposed to a high seismic risk due to local shallow and regional strong intermediate-depth seismic sources and that the available strong-motion database is quite limited and therefore not at all representative of the real hazard. The problem of seismic microzonation is of crucial importance for Sofia due to rapid urbanization at the national level and to the significant growth of the city that has led to the construction of a large volume of new residential and high-rise administrative and business buildings. Sofia is exposed to a high seismic risk. Macroseismic intensities in the range of VIII–X (MSK) can be expected in the city. The earthquakes that influence the hazard in Sofia originate either beneath the city or are caused by seismic sources located in a radius of 40–300 km. The city is also affected by remote seismic zones located in Turkey, Greece and Romania. The built environment is particularly vulnerable to the long-period elements of the Vrancea seismic zone in Romania. The high seismic risk and the lack of instrument records of regional seismicity require the development of a viable seismic microzonation procedure that supplies seismic input consistent with current codes (norms) and considers local site geology in detail as well. In this study, the results of applying a seismic microzonation procedure for designing and constructing a 34-storey administrative building in Sofia are shown. Both regional (20–300 km zone) and far-distant seismicity (zone with radius larger than 300 km) were analyzed in order to define characteristic parameters for probable earthquake scenarios. Both deterministic and probabilistic seismic hazard estimates were made. On the basis of the analyses, accelerograms were generated considering one-dimensional linear models and making use of the geomechanical and geophysical characteristics of the soil at the construction site that were obtained by in situ ?measurements. Using the results obtained, seismic risk estimates and seismic monitoring prescriptions for the planned building are provided.
NATO Science for Peace and Security Series C: Environmental Security, 2009
ABSTRACT Recently published data on seismic hazards due to strong, intermediate-depth Vrancea ear... more ABSTRACT Recently published data on seismic hazards due to strong, intermediate-depth Vrancea earthquakes in the area around the city Recently published data on seismic hazards due to strong, intermediate-depth Vrancea earthquakes in the area around the city of Russe is summarized including a review of analyses of available data, both macroseismic and instrument, and of recent theoretical of Russe is summarized including a review of analyses of available data, both macroseismic and instrument, and of recent theoretical seismic hazard estimates. A snapshot of the development of a strong motion registration system is offered, and the benefits seismic hazard estimates. A snapshot of the development of a strong motion registration system is offered, and the benefits of seismic monitoring in the region are discussed. Transforming data produced by seismic monitoring instruments into information of seismic monitoring in the region are discussed. Transforming data produced by seismic monitoring instruments into information for decision makers (e.g. emergency managers, earthquake engineers) are summarized including analytical steps that differ for decision makers (e.g. emergency managers, earthquake engineers) are summarized including analytical steps that differ depending on the type of data and the nature of the decision. depending on the type of data and the nature of the decision.
The intermediate-depth (70-180 km) earthquakes of the Vrancea (Romania) source zone produce the m... more The intermediate-depth (70-180 km) earthquakes of the Vrancea (Romania) source zone produce the most significant seismic hazard to Romania and its neighboring countries, in particular to the Republic of Moldova, Ukraine, and Bulgaria. Analyses of the macroseismic data of these events revealed several peculiar effects, which can be summarized as follows: the earthquakes affect very large areas with predominantly NE-SW
NATO Science for Peace and Security Series C: Environmental Security, 2009
An advanced modeling technique that allows us to compute realistic synthetic seismograms was used... more An advanced modeling technique that allows us to compute realistic synthetic seismograms was used to create a database of realistic synthetic accelerograms in a set of selected sites in the Sofia urban area. The accelerograms can be used to assess the local site response in terms of the response spectra ratio (RSR). The results of this study, i.e. time histories,
The earthquake record and the Code for design and construction in seismic regions in Bulgaria hav... more The earthquake record and the Code for design and construction in seismic regions in Bulgaria have shown that the territory of the Republic of Bulgaria is exposed to a high seismic risk due to local shallow and regional strong intermediate-depth seismic sources. The available strong motion database is quite limited, and therefore not representative at all of the real hazard. The application of the neo-deterministic seismic hazard assessment procedure for two main Bulgarian cities has been capable to supply a significant database of synthetic strong motions for the target sites, applicable for earthquake engineering purposes. The main advantage of the applied deterministic procedure is the possibility to take simultaneously and correctly into consideration the contribution to the earthquake ground motion at the target sites of the seismic source and of the seismic wave propagation in the crossed media. We discuss in this study the result of some recent applications of the neo-determi...
The study presents and solves the 2-D elastodynamic model for seismic in-plane wave propagation i... more The study presents and solves the 2-D elastodynamic model for seismic in-plane wave propagation in laterally inhomogeneous geological profiles imbedded in a vertically inhomogeneous half-space in which an earthquake source is buried. To this end, an efficient hybrid modal summation-boundary integral equation method (MSM-BIEM) is developed and applied. The MSM is used as a tool for simulating wave propagation from the source position to the multilayered laterally inhomogeneous geological profile where the BIEM is applied. The proposed model and the hybrid tool are used to investigate the phenomena of site effects. In fact, such a methodology has the potential to investigate the combined effects of different physical phenomena like surface topography, lateral inhomogeneity and the existence of water saturation in soils on the estimation of site effects. The model and hybrid computational tool developed are applied to contribute to the seismic risk analysis of the Bulgarian capital Sofia.
A study of the site effects and the microzonation of Sofia region, based on the modeling of seism... more A study of the site effects and the microzonation of Sofia region, based on the modeling of seismic ground motion along three cross sections were carried out. Realistic synthetic strong motion waveforms have been computed for an earthquake scenario applying a hybrid modeling method, based on the modal summation technique, finite differences scheme and neural modeling. Realistic synthetic seismic signals have been generated for all sites of interest. Two groups of experiments have been performed, where in first group the ground motion is modeled for one-dimensional layered anelastic media, applying an algorithm based on the modal summation method. In second group of experiments the ground motion is modeled for two-dimensional laterally heterogeneous media and with implementation of neural network, learned and trained with real earthquake seismic records. The aim of suggested deterministic modeling is to provide site response estimates at Sofia due to the chosen earthquake scenarios a...
The intermediate-depth earthquakes in Vrancea (Romania) are particularly notable in the group of ... more The intermediate-depth earthquakes in Vrancea (Romania) are particularly notable in the group of the European earthquakes. The scope of this work is to study the seismic effects of the Vrancea seismogenic zone in NE Bulgaria, with particular attention to the towns of Russe, Varna, Sofia capital.This study is limited to the question about the level of the ground motions at North East Bulgaria in terms of recorded spectral amplitudes during the 1986 and 1990 Vrancea strong earthquakes. For this purpose we discuses: (1) a schematic geological-geotechnical outline; (2) the strong ground motion records in NE Bulgaria, due to Vrancea strong earthquakes; (3) the description of the regional seismicity and a review of the available recurrence and attenuation relationships; (4) the results from the strong motion records analysis. The results of this study confirm the significant influence of the Vrancea intermediate-depth seismogenic zone on the sites of Russe, Varna, Sofia and vicinity and t...
NATO Science for Peace and Security Series C: Environmental Security, 2009
The study presents and solves the 2-D elastodynamic model for seismic in-plane wave propagation i... more The study presents and solves the 2-D elastodynamic model for seismic in-plane wave propagation in laterally inhomogeneous geological profiles imbedded in a vertically inhomogeneous half-space in which an earthquake source is buried. To this end, an efficient hybrid modal summation-boundary integral equation method (MSM-BIEM) is developed and applied. The MSM is used as a tool for simulating wave propagation from the source position to the multilayered laterally inhomogeneous geological profile where the BIEM is applied. The proposed model and the hybrid tool are used to investigate the phenomena of site effects. In fact, such a methodology has the potential to investigate the combined effects of different physical phenomena like surface topography, lateral inhomogeneity and the existence of water saturation in soils on the estimation of site effects. The model and hybrid computational tool developed are applied to contribute to the seismic risk analysis of the Bulgarian capital Sofia.
NATO Science for Peace and Security Series C: Environmental Security, 2009
The earthquake record and the code for designing and constructing buildings in seismic regions in... more The earthquake record and the code for designing and constructing buildings in seismic regions in Bulgaria have shown that the country is exposed to a high seismic risk due to local shallow and regional strong intermediate-depth seismic sources and that the available strong-motion database is quite limited and therefore not at all representative of the real hazard. The problem of seismic microzonation is of crucial importance for Sofia due to rapid urbanization at the national level and to the significant growth of the city that has led to the construction of a large volume of new residential and high-rise administrative and business buildings. Sofia is exposed to a high seismic risk. Macroseismic intensities in the range of VIII–X (MSK) can be expected in the city. The earthquakes that influence the hazard in Sofia originate either beneath the city or are caused by seismic sources located in a radius of 40–300 km. The city is also affected by remote seismic zones located in Turkey, Greece and Romania. The built environment is particularly vulnerable to the long-period elements of the Vrancea seismic zone in Romania. The high seismic risk and the lack of instrument records of regional seismicity require the development of a viable seismic microzonation procedure that supplies seismic input consistent with current codes (norms) and considers local site geology in detail as well. In this study, the results of applying a seismic microzonation procedure for designing and constructing a 34-storey administrative building in Sofia are shown. Both regional (20–300 km zone) and far-distant seismicity (zone with radius larger than 300 km) were analyzed in order to define characteristic parameters for probable earthquake scenarios. Both deterministic and probabilistic seismic hazard estimates were made. On the basis of the analyses, accelerograms were generated considering one-dimensional linear models and making use of the geomechanical and geophysical characteristics of the soil at the construction site that were obtained by in situ ?measurements. Using the results obtained, seismic risk estimates and seismic monitoring prescriptions for the planned building are provided.
NATO Science for Peace and Security Series C: Environmental Security, 2009
ABSTRACT Recently published data on seismic hazards due to strong, intermediate-depth Vrancea ear... more ABSTRACT Recently published data on seismic hazards due to strong, intermediate-depth Vrancea earthquakes in the area around the city Recently published data on seismic hazards due to strong, intermediate-depth Vrancea earthquakes in the area around the city of Russe is summarized including a review of analyses of available data, both macroseismic and instrument, and of recent theoretical of Russe is summarized including a review of analyses of available data, both macroseismic and instrument, and of recent theoretical seismic hazard estimates. A snapshot of the development of a strong motion registration system is offered, and the benefits seismic hazard estimates. A snapshot of the development of a strong motion registration system is offered, and the benefits of seismic monitoring in the region are discussed. Transforming data produced by seismic monitoring instruments into information of seismic monitoring in the region are discussed. Transforming data produced by seismic monitoring instruments into information for decision makers (e.g. emergency managers, earthquake engineers) are summarized including analytical steps that differ for decision makers (e.g. emergency managers, earthquake engineers) are summarized including analytical steps that differ depending on the type of data and the nature of the decision. depending on the type of data and the nature of the decision.
The intermediate-depth (70-180 km) earthquakes of the Vrancea (Romania) source zone produce the m... more The intermediate-depth (70-180 km) earthquakes of the Vrancea (Romania) source zone produce the most significant seismic hazard to Romania and its neighboring countries, in particular to the Republic of Moldova, Ukraine, and Bulgaria. Analyses of the macroseismic data of these events revealed several peculiar effects, which can be summarized as follows: the earthquakes affect very large areas with predominantly NE-SW
NATO Science for Peace and Security Series C: Environmental Security, 2009
An advanced modeling technique that allows us to compute realistic synthetic seismograms was used... more An advanced modeling technique that allows us to compute realistic synthetic seismograms was used to create a database of realistic synthetic accelerograms in a set of selected sites in the Sofia urban area. The accelerograms can be used to assess the local site response in terms of the response spectra ratio (RSR). The results of this study, i.e. time histories,
The earthquake record and the Code for design and construction in seismic regions in Bulgaria hav... more The earthquake record and the Code for design and construction in seismic regions in Bulgaria have shown that the territory of the Republic of Bulgaria is exposed to a high seismic risk due to local shallow and regional strong intermediate-depth seismic sources. The available strong motion database is quite limited, and therefore not representative at all of the real hazard. The application of the neo-deterministic seismic hazard assessment procedure for two main Bulgarian cities has been capable to supply a significant database of synthetic strong motions for the target sites, applicable for earthquake engineering purposes. The main advantage of the applied deterministic procedure is the possibility to take simultaneously and correctly into consideration the contribution to the earthquake ground motion at the target sites of the seismic source and of the seismic wave propagation in the crossed media. We discuss in this study the result of some recent applications of the neo-determi...
This volume summarizes the main findings of the NATO Science for Peace Project SfP-980468 Harmoni... more This volume summarizes the main findings of the NATO Science for Peace Project SfP-980468 Harmonization of Seismic Hazard and Risk Reduction in Countries Influenced by Vrancea Earthquakes. It addresses the problems of regional seismic hazard assessment, its application to the Vrancea zone that influences the territories of Romania, Bulgaria, and Moldova, and provides guidelines for seismic risk reduction in the target countries.
The contributions focus on key problems of the Vrancea area and related strong ground motion. The book covers a range of topics: from hazard assessment to site effects and microzonation, from protection of historical buildings to the study of the dynamic properties of the soft soils and paleoseismology.
Researchers, practitioners, experts, and students will benefit from reading this book and having it as a reference in the years to come.
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The contributions focus on key problems of the Vrancea area and related strong ground motion. The book covers a range of topics: from hazard assessment to site effects and microzonation, from protection of historical buildings to the study of the dynamic properties of the soft soils and paleoseismology.
Researchers, practitioners, experts, and students will benefit from reading this book and having it as a reference in the years to come.