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A new probabilistic seismic hazard assessment for Albania is carried out using the smoothed gridded seismicity approach. Albania’s earthquake catalogue is already revised and expanded, covering a study area limited by 38 − 44.5°N Latitude and 18 − 24°E Longitude, and the time period from 58BC to 31/12/2008. The ground motion hazard map is presented over a 10 km grid in terms of peak ground acceleration for 10% probability of exceedance in 50 years, corresponding to 475-year return period. The reference site condition is firm rock, defined as having an average shear-wave velocity in the upper 30 m of the crust of 800 m/sec. It is the standard reference site condition used by the European seismic code (Eurocode 8) for seismic zonation and building codes. The main finding is that if this map is accepted as a reference indicator to establish a new regulatory national seismic zonation, design acceleration will be much higher than that applied in the current regulation. This implies that the competent authorities should take into consideration the obtained results to improve the existing design code in a more reliable and realistic basis in order to increase the safety level of constructions in the country.

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The seismic hazard assessment in dense-populated areas and the strategic objectives design are based on the study of seismicity of the seismogenic sources (which can have an effect at the site above a specified minimum level that is considered risky) and the attenuation between focus and site. The purpose of this paper is to provide a complete set of information required for a probabilistic assessment of the seismic hazard in the southeast Romania relative to the following seismic sources: Vrancea zone (in the crust and intermediate-depth domains), Predobrogean depression zone, Intramoesian zone and Shabla-Dulovo (Bulgaria) zone. As an example, the obtained input parameters are used to evaluate the seismic hazard distribution due to the crustal earthquakes applying the McGuire's procedure (1976). These preliminary results are in good agreement with the previous research based on deterministic approach (Radulian et al. 2000).

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The investigations of seismicity, tectonics and geology of the territory of Republic of Macedonia that have been performed so far have pointed out the direct relationship between the earthquake occurrence and tectonic processes. To define a seismogene source and earthquake occurrence, it is necessary to know the geological evolution of the terrain particularly in contemporary conditions. In the investigated area, earthquakes have exclusively been of a tectonic origin wherefore the greatest attention has been paid to the activity of the fault structures in the Vardar zone, the correlation between the epicenters of occurred earthquakes and the geological media through which the seismic waves propagate. The seismotectonic map of the Vardar zone clearly shows that the stretching direction of the fault structures correlates with the epicenters of occurred earthquakes. The seismicity model formulated on the basis of data from the seismological and seismotectonic investigations of the region has been the starting point in defining the seismic hazard. Two approaches have been proposed for definition of a seismic model to be used in defining the seismic hazard. A comparison between these models has also been made.

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We present a short review of the most recent results coming from the numerical modeling of seismic hazard and interpretation of the new observations provided by the recently installed seismic stations in Romania. There are still controversial questions related to the asymmetric distribution of the ground motion radiated by the Vrancea intermediate-depth earthquakes and which is the main factor responsible for this particular distribution: seismic source, structural model, site effects or vulnerability. Our main goal is to provide a solution to this key problem, with direct implications upon the seismic hazard assessment. NE-SW elongation of the isoseismals and the maximum values in the Romanian Plain are well explained by the source radiation pattern and the average structural model. The attenuation toward NW is shown to be a frequency-dependent effect, much more important in the high frequency range (≯1 Hz). We conclude that the present seismic hazard of Romania, computed by the deterministic approach, fits well, as a first approximation, the ground motion distribution for the low-frequency band, and the apparent contradiction with the historically-based intensity maps arises mainly from a systematic difference in the vulnerability of the buildings in the intra- and extra-Carpathians regions.

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A new technique is developed to perform a deterministic hazard analysis in terms of physical parameters, i.e. displacements, velocities, maximum accelerations, and civil engineering specific ones, design accelerations. The method is adapted for the specific features of the Romanian Plain seismicity including the latest theoretical results in both seismotectonic and prediction fields, and data acquisitions. The deterministic analysis is performed computing free surface synthetic seismograms corresponding to different seismic sources and structural models, for crustal and intermediate-depth events separately. The DGA (design ground acceleration) greatest values and the NS and EW components resultant for the velocities and horizontal displacements are considered as a measure for seismic hazard level.

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Deterministic seismic hazard computations were performed along four different profiles across the downtown of Budapest. Synthetic seismograms were computed by the so called “hybrid technique”. By applying the hybrid technique it is possible to take into account the focal source, the path and the site effect together. Four independent computations have been performed using the same seismic source but different profiles. The parameters of the seismic source were adopted from the parameters of the well-known 1956 Dunaharaszti earthquake. The focal mechanism and the homogeneous and heterogeneous parts of the profiles are known from geophysical and geological data of the investigated area.As the results of the computations PGA (peak ground acceleration) grid maps of the downtown of Budapest for the three different components came into existence. Furthermore spectral acceleration (response spectra, SA) and RSR charts of the synthetic seismograms for the four different profiles were created. The PGA grid maps show that the maximal PGA values are situated at the eastern (Pest) part of the downtown, and their values are 50–200 cm/s 2 .For the downtown of Budapest a special seismic risk map have been prepared. This special seismic risk map were created on the basis of the difference between the maximal amplitude frequencies of SA of synthetic seismograms and the building’s eigenfrequencies at every 0.1 km 2 of the downtown. In order to determine the building’s eigenfrequencies microseismic noise measurement were performed at 6 different buildings in the downtown. The special seismic risk map shows that the buildings situated at the hilly western section of the downtown have higher seismic risk than the ones at the flat eastern part.

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In this paper, a theory describing the possible origin of shallow depth earthquakes occurring within the sedimentary depressions of the Pannonian Basin is presented. In addition, the seismicity of Budapest is re-evaluated by synthetic seismogram based deterministic seismic hazard estimation.

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A probabilistically based hazard map of Albania expressed in terms of PGA for 475 years of return period following the spatially smoothed seismicity approach proposed by Frankel (1995) and developed by Slovenian researchers (Lapajne et al. 1997), is presented.  Taking advantage of this development, an effort has been made to analyze the parameters of site-dependent acceleration response spectra parameters of the current seismic design code KTP-N.2-89 in Albania.

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Attenuation specific from Vrancea intermediate-depth focus toward SE is revised at length in order to re-evaluate the seismic hazard at the nuclear power plant (NPP) Cernavoda. To this aim, we took into consideration all the strong motion data available for the region and test a large range of relationship types. Since the instrumental data are limited as magnitude and  depth intervals, the extrapolation based on the attenuation laws deduced from these data to great magnitudes is very instable and must be carefully considered. The extrapolation outside the characteristic domain of the available database leads to large deviations, especially at large magnitudes and for the relations which contain the depth as independent parameter.

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We applied deterministic and probabilistic methodologies for seismic hazard assessment at Tirana city, expressed in terms of horizontal peak ground acceleration (PGA). The deterministic evalues of PGA are determined according to the scenario R = 6.4 km and M max = 6.0, while the probabilistic ones have been assessed applying the smoothed seismicity approach. The results that derive from the two methodologies show equal values of PGA for the selected site inside Tirana city and higher than the PGA values established by the official maps as well as the actual seismic coefficients that are being applied by the actually in force national design code KTP-N.2–89 for Tirana area.

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