Seismic site effects in Istanbul

Abstract

The objective of this study is to identify the spacial variations in several seismichazards, such as soil amplification, in the most historic part of Istanbul, Turkey,and to map these differences accordingly. An assessment of microzonationpractices-to-date is followed by an overview of the historical seismicity of theregion, the local tectonic regime, geology and topography. Microtremormeasurements were conducted and accelerometers were installed which providedrecords of three small earthquakes. The results in terms of relative amplification ofsoft ground conditions with respect to harder and the horizontal with respect tovertical component of motion are calculated for both microtremor and earthquakerecords. A good correlation is evident between the microtremor and earthquakesfor both types of spectral ratios, with regards to predominant frequencies andrelative amplification. Frequencies identified by analytical studies as well as thefield investigations appear to reflect the fundamental frequencies of the differentsurface ground conditions. Comparison of amplification predicted by microtremor,earthquake, and analytical studies with past earthquake damage distributionsindicate that local site conditions were not the primary cause of the destruction.The results of each part of this study are displayed in map format.Keywords: Earthquake, Amplification, Microtremor, Microzonation, StrongGround Motion .