An approach of microzonation of the Sofia city

Abstract

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.