Ivanka Paskaleva

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...

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.

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 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

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,

ABSTRACT The study solves 2D elastodynamic model for seismic in-plane wave propagation in laterally inhomogeneous geological profiles situated in a vertically inhomogeneous half-space with a seismic source. For the aim, an efficient hybrid Modal Summation-Boundary Integral Equation Method (MSM-BIEM) is applied. The MSM is used as a tool for the simulation of wave propagation from the source position to the local multilayered laterally inhomogeneous geological profile, where the BIEM is applied. The BIEM is based on the frequency-dependent fundamental solution of the governing equation in elastodynamics and the hybrid method works in the frequency domain. The inverse FFT solution is applied to obtain time histories. The hybrid tool is applied to several models for the investigation of local site effects due to: (a) the impedance contrasts between soil layers, (b) surface topography and lateral inhomogeneity, (c) the seismic source properties and (d) the existence of water saturation in soils. The application of the modeling tool is a contribution to the seismic risk analysis of Sofia city.

An advanced procedure for ground motion modelling, capable of synthesizing the seismic ground motion from basic understanding of fault mechanism and seismic wave propagation, is applied to the case studies of Bucharest, Romania and Russe (NE Bulgaria), exposed at Vrancea seismic hazard. Synthetic seismic signals along predefined geological cross sections in Bucharest and Russe have been computed and the energetic

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ABSTRACT An analytical deterministic technique, based on the simultaneous account of the fault mechanism and seismic wave propagation, has been applied to generate synthetic seis- mic signals at Russe, NE Bulgaria due to the strongest intermediate-depth Vrancea earthquakes, which occurred during the last century (1940, 1977, 1986 and 1990). The computations have been validated by comparison with the available observations, i.e. accelerograms and macroseismic intensity data. The synthetic signals have been gen- erated varying the seismic source moment tensor and the Vp/Vs ratio of the uppermost layers along the investigated profile. Response and energetic spectra are calculated for the whole synthetic signals set. The obtained results show that all ground motion components give a significant contribution to the seismic input and that they can be influenced in similar degree by the investigated parameters. Therefore the seismic in- put (also at remote distances), should consider enough earthquake scenarios, and can be constructed via waveform modelling, considering all possible factors influencing the ground motion.

... The calculations are performed separately for the sH and P-sV waves. ... The solid line Îmax = 20 cm/s (Duvall and Fogelson 1962) limits the area where major degree of damages have to be expected for old residential buildings and I0 ~IX MsK) (solakov et al. 2001). ...

... 4 and Table I, the best fit in terms of peak acceleration (PGA), velocity (PGV), displacement (PGD), PGV/PGD ratio, A95 and response spectra, sA 5%, has been obtained for the TRA component, (eg observed PGA = 14.10 against computed PGA = 13.90 cm/s2). ...

ABSTRACT The city of Sofia has the densest population of Bulgaria — around 1.27 million people. The capital is exposed to high seismic risk. According to the Bulgarian seismic code, Sofia has been included in a seismic category characterized by intensity IX (MSK), which corresponds to a horizontal acceleration of 0.27 g for the anchoring of the elastic response spectrum. Because of the lack of instrumental seismic data, realistic synthetic strong motion waveforms for two opposite positions of seismic sources, have been generated for an expected earthquake scenarios (M = 7) along three geological profiles. A hybrid modeling method has been used for the modeling, which is based on the modal summation technique and finite difference scheme. The calculation has been done using an extended source model. The site effect is represented in terms of response spectra ratio (RSR), with respect to a bedrock model. The three components synthetic seismograms, computed in the domain of displacement, velocity and acceleration have been processed to extract some parameters very useful for engineering applications.

ABSTRACT This work focuses on the assessment of seismic risk issues associated with the potassium salt deposit of Provadia and Soligorsk, with the monitoring provided by Belarusian and Bulgarian specialists in the framework of a bilateral project. The long-term studies 1983–2005 of the only terrestrial Bulgarian salt deposit (Provadia, φ = 43.06°N, λ = 27.45°E) and Belarusian (Starobin φ = 52.84°N, λ = 27.47°E) in connection with the observed higher seismic activity and probable manifestations of technogenic seismicity in the region is presented. The characteristic features of the seismic processes as the identity of the curves of recurrence of seismic events of the energy range of 4–8 are discussed. A quasi-periodic character of the seismicity activation in time against the general trend of seismicity activation is established. It is shown that the zones of the epicenters of the seismic events are larger that mining areas. Some differences in the pattern of seismic processes, such as: 1. the seismic activity in the range of small energies (K = 4–8) is higher in the Soligorsk region; 2. events of the higher energy class, K > 9 are characteristic of the Provadia region.

... All stations were equipped with high resolution digital acquisition systems RefTek DAS 130/01 (Dimitrova et al ... of the structures in the region of Provadia, for pillar design and reestimations of their bearing capacity and for eventual forecast of the behaviour of the rail road crossing ...