Full Length Research Paper

Seismic microzonation studies in Sisli, Istanbul, Turkey

Ferhat Ozcep¹*, Savas Karabulut¹, Burcu Korkmaz¹ and Halil Zarif²

1Istanbul University, Faculty of Engineering, Department of Geophysical Engineering Avcilar, 34850, Istanbul.
2Istanbul University, Faculty of Engineering, Department of Geological Engineering Avcilar, 34850, Istanbul.

*Corresponding author. E-mail: ferozcep@istanbul.edu.tr. 

Accepted 17 February, 2010

Abstract

The main purpose of this study is to provide an application of seismic microzonation at small scales. 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 (15%) in a given time period (50 years). By using deterministic seismic hazard analysis, the magnitudes were estimated by the three rapture (with three different fault, 108, 119 and 174 km) model of North Anatolian Fault Zone in Marmara Region. By using both mode of analysis (deterministic and probabilistic), magnitude of design earthquake was taken as 7.6. From these design earthquakes, accelerations were estimated for several distances (from 25 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 refraction measurements and Standard Penetration Test (SPT test data for the area of Sisli where, the important part of Istanbul city is located. Also microtremor and earthquake data were evaluated to compare the obtained characteristic site period data. Furthermore Vs30 values are compared by MASW techniques. Finally, a seismic microzonation map are prepared integrated use of all geophysical and geotechnical data. According to Eurocode soil classification, study area is mainly formed from B type soils. A little part of study area is located on C and A type soils. Characteristic site periods obtained by seismic methods is in agreement with strong (earthquake) and weak (ambient noise) motion spectral values at some part of study area.

Key words: Microzonation, geophysical and geotechnical analyses, soil amplification, Istanbul, Turkey.