Geoscience Reference
In-Depth Information
CHAPTER 4
SOURCE AND SITE FACTORS IN MICROZONATION
AtillaAnsal and Gokc¸eTonuk
Department of Earthquake Engineering, Kandilli Observatory and Earthquake
Research Institute, Bogazi¸i University, Istanbul, Turkey
ansal@boun.edu.tr
Abstract.
Thecomprehensivecalculationofsitespecificearthquakecharacteristicsontheground
surface for microzonation requires input acceleration time histories compatible with the regional
earthquake hazard representing source factors. Real and simulated acceleration records were used
as input for site response analyses to evaluate the reliability and to observe the induced variability.
Thesecondcomponentofsitespecificcalculationsissitecharacterisationandestablishmentofrep-
resentative soil profiles down to engineering bedrock that represent the site factors. Grid systems
with 250m
×
250m cells were adopted to define the site conditions in terms of representative soil
profiles for each cell. The third component of the site specific calculations is the analytical pro-
cedure used for site response analysis and the interpretation scheme of the calculated site specific
parameters. Parametric studies were conducted for the probabilistic assessment of microzonation
with respect to ground shaking intensity and liquefaction susceptibility as well as for vulnerabil-
ity assessment based on acceleration response spectra, peak ground accelerations, and cyclic shear
stressvariation withdepth, calculated bysite response analyses foreach cell.
1. Introduction
Site specific free field earthquake characteristics on the ground surface are the essential
components for microzonation with respect to ground shaking intensity, liquefaction
susceptibility, and for the assessment of the seismic vulnerability of the urban environ-
ment. The microzonation methodology can be considered as composed of three stages.
In the first stage, regional seismic hazard analyses need to be conducted to estimate
earthquake characteristics on rock outcrop for each cell. In the second stage, the rep-
resentative site profiles should be modelled based on the available borings and in-situ
tests. The third stage involves site response analyses for estimating the earthquake char-
acteristics on the ground surface and the interpretation of the results for microzonation
(Ansal et al., 2004a,b). In addition to the generation of base maps for urban planning,
microzonation with respect to spectral accelerations, peak accelerations and velocity on
the ground surface can be used to assess the vulnerability of the building stock (Ansal
et al., 2005a, 2006b) and lifelinesystems.
Theregionalearthquakehazardmaybebasedonprobabilisticordeterministicapproach.
In the case of microzonation for urban planning, it is preferable to adopt a probabilistic
earthquake hazard assessment but in the case of earthquake scenarios for estimating
