A framework for the analysis of seismic risk to lifelines, with references to the case of Vrancea earthquakes, is presented. The framework dealt with is probability based. It relies on the use of stationary, Poissonian, models, while complications raised by the consideration of non-stationarity (as e.g. those raised by the consideration of the evolutionary character of vulnerability of some elements at risk) are avoided. The elements at risk considered may be lifelines as a whole, or components of them. Seismic action and seismic hazard are considered, alternatively, at source level or at site level. Radiation/attenuation features are defined in this frame. Adverse effects of earthquakes (referred to in general as damage) may be related alternatively, in specific ways, to the various elements at risk considered. Seismic vulnerability may be considered as source related or as site related, too. Various exposure patterns are considered. Alternative models of functionality are discussed and risk characteristics are generally related to them. The definition of entities referred to are expressed in probabilistic terms and convolution relations, leading up to risk estimates, are given, basically in discrete terms. In connection with the features of Vrancea earthquakes, specific recurrence characteristics and needs of additional specification, considering the variability of source mechanisms, are discussed. Possibilities of simplification of the approach, in order to avoid the excessive needs of basic data and of computing effort raised by a rigorous approach, are discussed, too.
Authors:D. Lungu, A. Aldea, S. Demetriu, and I. Craifaleanu
International Conference on Earthquake Hazard and SeismicRisk Reduction, Yerevan, Armenia, Kluwer Academic Publisher, 2000, 281--289.
Second International Conference on Earthquake Hazard and SeismicRisk Reduction
Authors:K. Gribovszki, F. Schulek-Tóth, and P. Varga
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
.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
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.
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.