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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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This study is related to the particular strong intermediate-depth Vrancea earthquakes. Its purpose is to confirm once again the significant influence of the seismic source mechanism to the seismic input at a given site through estimates of different engineering parameters, used to describe the damage potential of the ground motion due to an earthquake. Real and synthetic time-series have been used in the computations. The synthetic seismic wavelets have been computed applying the neo-deterministic seismic hazard assessment procedure and the relevant software and hardware facilities at the Department of Earth Sciences, University of Trieste, Italy. To derive the ground motion parameters of interest, all seismic signals have been uniformly processed by the Seismosignal software.

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In this article, stochastic finite-fault simulation combined with site response analysis is used to understand the spatial distribution of ground motion in Guwahati city due to three damaging earthquakes. The rock level ground motion for the scenario earthquakes is generated based on the stochastic finite-fault methodology. These simulated motions are further amplified up to the surface by equivalent linear site response analyses using the available borelog data at 100 different locations in Guwahati city. A set of twenty simulated rock level time histories for each event, are used to compute the surface level ground motion. Response spectra are computed and the results are presented in the form of contour maps, at selected natural periods. The mean amplification due to local soil deposit is as high as 2.2 at most of the sites in Guwahati city. Based on these simulated motions, an average site correction factor is obtained for soil sites in Guwahati city. The standard error in the simulated response spectra is also reported. The contour maps obtained will be useful in identifying vulnerable places in Guwahati city.

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The investigations presented in this paper were aimed at empirical definition  of ground motion under Vrancea earthquakes.  They were based on the recorded accelerogrammes from the occurred strong Vrancea earthquakes of 1977, 1986 and 1990 obtained from the accelerographs installed in the territory of former Yugoslavia, Romania and Bulgaria. A methodological approach to empirical prediction of ground motion parameters under strong earthquake effects was developed and empirical attenuation laws of horizontal peak ground acceleration (PGA) were defined.  A new empirical mathematical model was applied. In this model the amplitudes of strong ground motion are in function of earthquake magnitude, epicentral distance, focal depth, azimuth of the instrument location in respect to  the radiation pattern and the ratio between the semi-axes of the seismic field  ellipse. Through the so called non-homogeneity function of the region, the model indirectly involves the effect of the focal mechanism and the non-homogeneity of the region through which the seismic waves propagate.  The mathematical model applied in these investigations contributed to the  empirical definition of the attenuation laws that play an important role in seismic  hazard analyses and hence in evaluation of the seismic hazard a country or a  region is exposed to.  The results obtained from these investigations are important not only for   Macedonia but for the entire Balkan region and beyond.  The presented methodology and the applied mathematical model of functional relationships are of a particular importance since they are different from the empirical models of strong ground motion that have so far been applied in the world.

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It is well known that surface geology may significantly affect strong ground motion and hence it should be incorporated into seismic hazard estimation at a specific site. Numerical and empirical methods are used to determine the site effect. On areas with moderate seismicity the empirical methods are based on microtremor measurements. Solely the single station methods, for example the H/V spectral ratio technique, could be used in the absence of a nearby reference station situated on rock site. The one year long noise measurements of 8 stations belonging to the Hungarian Microseismic Monitoring Network have made it possible the testing of this method. The stations are situated in the middle part of Hungary. All seismometers are triaxial LE-3D high sensitivity 1 Hz geophones. Three stations are situated on hard rocks while five ones on loose site above a deep sedimentary basin with more than 1000m thick sediments. The large amount of noise data have made it possible to examine the stability of the method. The examinations have shown that the computed spectral ratio curves are very stable in time. While all stations on rock sites show nearly at H/V spectral ratio, all stations on soft sites show a peak at very low, 0.1- 0.2Hz frequencies. Analytical computations have been carried out to verify this low frequency behaviour and have shown that these peaks are due to the fundamental frequency of the overall sediment thickness. H/V ratios have also been calculated from seismograms of weak local earthquakes, so they could be compared with ratios obtained from noise measurements.

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compiled strong ground-motion database for Turkey, Paper presented at Joint Meeting of WA1 and WA3 of IAEA EBP Seismic , Vienna, 18 May 2009. Augusti G. Some observations on the calculation of structural failure

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used to describe this property, which is important for the analysis of different dynamic problems where the strain is of high amplitude (e.g., strong ground motion during earthquakes). The shear modulus degradation curve can be obtained from the

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