كليدواژه :
Microtremor , H/V , Microzonation , Spectrum
چكيده فارسي :
Seismic hazard assessment of big cities is imperative to mitigate the potential damage and loss of life
due to earthquakes. Local ground conditions substantially affect the characteristics of incoming seismic
waves during earthquakes. Soft soil deposits amplify certain frequencies of ground motion and extend the
duration of the motion, thereby increasing earthquake damage. Seismic waves are trapped in the soft soil
layer and multi-reflection phenomenon occurs. As a result, the ground vibrates severely with a specific
dominant period. This period is called the predominant period of the ground, and the vibration of structures
on the surface is highly influenced by it.
Microtremor observations can be used to determine the dynamic properties of a site and, hence, can be
used for microzonation. In order to clarify the surface ground motion characteristics at Bojnord City, a
microtremor measurement grid has been designed. Different 1-hour microtremor measurings during day and
night have been carried out. The horizontal to vertical spectral ratio technique, also called Nakamuraʹs
method (Nakamura, 1989) or HVNR was used as a principal data processing procedure in order to extract the
experimental transfer function of the site. Fundamental frequencies of the sites using HVNR have been
extracted. Following this extraction, the city zonation considering the low-rise, mid-rise and high rise
building has been carried out and finally distribution maps of site periods and peak ground acceleration
throughout the city were developed.
