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Fast and efficient use of
geophysical and geotechnical data in urban microzonation
studies at small scales: Using Sisli/Istanbul (Turkey) as
example
Burcu Korkmaz
and Ferhat Ozcep*
Istanbul
University, Faculty of Engineering, Department of
Geophysical Engineering Avcilar, 34850, Istanbul.
*Corresponding author. E-mail:
ferozcep@istanbul.edu.tr.
Tel: +90 212 4737070 Ext. 17570. Fax: +90 212 4737180.
Accepted
19 January, 2010. |
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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). |
