The aim of our study is to determine the design ground acceleration values at different parts of Debrecen along two profiles crossing the city. Synthetic seismograms are computed by the so called “hybrid technique”. This technique consists of the modal summation method, followed by finite difference modelling. Two independent computations have been performed using two different seismic sources and profiles. In both computations the seismic sources have been located in the so called “Mobile Zone”. The Mobile Zone is a seismically active fault system between the villages of Hosszúpályi and Gálospetri. The focal mechanism and the homogeneous and heterogeneous parts of the profile are known from geophysical and geological data of the investigated area. The maximum response spectra ratio values of the horizontal component are found below 1 Hz all along the profile and the frequencies below 1 Hz are in good agreement with the natural frequencies of the multi-storeyed buildings. Computed effective peak acceleration (EPA) values are found to be in good agreement also with the higher than 6° MSK macroseismic intensity values estimated from the assessment records of damages wrought by the 1834 Érmellék earthquake.
Authors:I. Paskaleva, G. F. Panza, F. Vaccari, and P. Ivanov
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.
Authors:G. Koleva, F. Vaccari, I. Paskaleva, E. Zuccolo, and G. Panza
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 (
= 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.