Fast and efficient use of geophysical and geotechnical data in urban microzonation studies at small scales: Using Sisli/Istanbul (Turkey) as example

Abstract

The main purpose of this study is to provide the combined use of geophysical and geotechnical data in context of microzonation. Earthquake occurrences on the North Anatolian Fault, being usually characterized and well documented in history, a time dependent model can be reasonably used for the probabilistic assessment of the seismic hazard in Istanbul. For the study area, the probabilistic seismic hazard analysis was determined by using Poisson probabilistic approaches. The hazard gives the probability that a given level of acceleration will be exceeded (30%) in a given time period (30 years). By using deterministic seismic hazard analysis, the magnitudes were estimated by the four rapture (with four different fault length, 108, 119 and 174 km) model of North Anatolian Fault Zone in Marmara Region. By using both analyses (deterministic and probabilistic), magnitude of design earthquake was taken as 7.6. From this design earthquake, accelerations were estimated for several distances (from 15 to 50 km) by several attenuation relations. In the second phase of the study, soil amplification factors and site characteristic periods were determined and estimated by seismic measurements and Standard Penetration Test (SPT test) data for the area of Sisli where the important part of Istanbul city is located. Geotechnical test data from boreholes and laboratory measurements were evaluated with geophysical data. Soil amplification values estimated by empirical relationships in terms of shear wave velocities are in the range of 1.0 and 2.1 values. Shear wave velocity (Vs, 30) values are 381.5 and 915 (m/s). Site characteristic period range is between 0.2 and 0.5 s. Key words: Microzonation, geophysical and geotechnical analysis, soil amplification, Istanbul (Turkey).