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  • Author or Editor: G. F. Panza x
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The aim of our study is to determine the design ground acceleration values at the whole territory of Debrecen and to accomplish the seismic risk map of Debrecen using synthetic seismograms. Synthetic seismograms are computed by the so called ``hybrid technique" along 11 different profiles crossing the city. The hybrid technique consists of the modal summation method, followed by finite difference modelling. 11 independent computations have been performed using the same seismic source but different profiles. The seismic source has been located in the so called “Mobile Zone”, which is a seismically active fault system in Érmellék region. 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 grid maps of Debrecen for the 3 different components and the spectral  acceleration (response spectra, SA) charts of the synthetic seismograms for the transversal components came  into existence. The seismic risk map of the city has been completed from the SA charts created from the synthetic seismograms and from the grid map of the buildings in Debrecen with different number of floors by applying GIS tools.

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A deterministic analytical procedure for ground motion modelling, combining both modal summation and mode coupling techniques has been implemented to obtain synthetic seismic signals at Russe, NE Bulgaria, due to  one of the strongest Vrancea intermediate-depth earthquakes, which occurred during the last century, May  30, 1990. The frequency content of the synthetic signals in different frequency ranges, up to 1 and 2 Hz, has been studied separately. The results of this study, i.e. time histories and related ground motions parameters, can be used for different earthquake engineering analyses, e.g. structural performance assessments.

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The capital of Bulgaria, Sofia is a growing city with population around 1.22 million. The city is exposed to a high seismic risk since it is placed in the centre of Sofia seismic area. Over the centuries in the town of Sofia the macroseismic intensities have been larger than IX (MSK). A study of the site effects and the microzonation of a part of metropolitan Sofia, based on a  modelling of seismic ground motion along three cross sections are presented. Realistic synthetic strong motion waveforms have been computed for an expected scenario earthquake (M=7) applying a hybrid modelling method, based  on the modal summation technique and finite differences scheme. The site amplification is determined in terms of response spectra ratio (RSR). A set of time histories and quantities of earthquake engineering interest are supplied, that allow the definition of six zones characterized by specific response spectra. The results from this study constitute a “database” that describes the ground shaking of the urban area.  The synthetic velocigrams are employed to calculate the distribution of the horizontal strain factor Log10e using a simplified relation between particle velocity and velocity of shear waves in the surface layer. It is shown  that it is possible to estimate liquefaction susceptibility in terms of standard penetration tests (SPT), Nvalues and initial over burden stress. Using the data for maximum particle velocity and empirical relationships developed from the Northridge earthquake, 1994 the distributions of the expected pipe breaks and red-tagged buildings for Sofia city are shown.

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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.

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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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Journal of Radioanalytical and Nuclear Chemistry
Authors: W. Plastino, G. Panza, C. Doglioni, M. Frezzotti, A. Peccerillo, P. De Felice, F. Bella, P. Povinec, S. Nisi, L. Ioannucci, P. Aprili, M. Balata, M. Cozzella, and M. Laubenstein

Abstract  

The ability to predict earthquakes is one of the greatest challenges for Earth Sciences. Radon has been suggested as one possible precursor, and its groundwater anomalies associated with earthquakes and water–rock interactions were proposed in several seismogenic areas worldwide as due to possible transport of radon through microfractures, or due to crustal gas fluxes along active faults. However, the use of radon as a possible earthquake’s precursor is not clearly linked to crustal deformation. It is shown in this paper that uranium groundwater anomalies, which were observed in cataclastic rocks crossing the underground Gran Sasso National Laboratory, can be used as a possible strain meter in domains where continental lithosphere is subducted. Measurements evidence clear, sharp anomalies from July, 2008 to the end of March, 2009, related to a preparation phase of the seismic swarm, which occurred near L’Aquila, Italy, from October, 2008 to April, 2009. On April 6th, 2009 an earthquake (Mw = 6.3) occurred at 01:33 UT in the same area, with normal faulting on a NW–SE oriented structure about 15 km long, dipping toward SW. In the framework of the geophysical and geochemical models of the area, these measurements indicate that uranium may be used as a possible strain meter in extensional tectonic settings similar to those where the L’Aquila earthquake occurred.

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