Istanbul geotechnical downhole arrays

Abstract

Geotechnical downhole arrays that record seismic ground response in near-surface layers are increasingly becoming one of the best sources of information for developing, verifying, and calibrating engineering analyses and design methods. Recently, three geotechnical downhole arrays have been installed in the European side of Istanbul, Turkey with efforts of Kandilli Observatory and Earthquake Research Institute (KOERI). The existing high seismic activity of the region increases the scientific importance of these downhole arrays. Each array is composed of one accelerometer on the ground surface and three or four borehole accelerometers at various depths along the soil profile with the deepest sensor located at the engineering bedrock level (V_s > 750 m/s). The arrays also provide reference bedrock motion for Rapid Response Network composed of 55 surface instruments operated by KOERI in the west European side of city. An important aspect of this paper is to introduce the recently-completed test sites emphasizing on their potential to generate valuable data for scientific community. Preliminary analysis of the recorded data provides evidence for significant site amplification of ground motion by the surface layers. Comparisons between the recorded and modeled response indicate that V_s 30 alone is a poor indicator of the amplification potential emphasizing the importance of site-specific analyses in predicting the ground response as opposed to empirical approaches.