Vulnerability evaluation of the urban area using the H/V spectral ratio of microtremors

Abstract

During the age of cities, buildings were constructed using different techniques, materials, styles and standard codes. Buildings have different responses to earthquake-related effects, depending on their materials and design rules. Soil layer specifications are recognized by different methods, including geotechnical, geophysical and the horizontal-to-vertical spectral ratios (H/V). The spectral ratio of microtremors was first introduced by Nakamura [14]. This method is useful in site characterization studies due to its low budget and easy use. In this paper, it is presented as a method for estimating the degree of vulnerability of structures using spectral ratio H/V. By applying a vulnerability study in the city of Shiraz, the predominant frequencies are derived for different parts of the city. The data is then used to define a coefficient of vulnerability for the earth. For this purpose, 11 different building structures including masonry, steel and concrete were selected. Then, the primary frequency and amplification of the microtremor H/V spectral ratio for buildings are obtained. Furthermore, the resonant frequency and amplification factor of the ground is calculated. The vulnerability index of soil Kg and the vulnerability of building Kb are defined. By comparing these coefficients, the damage factor η of buildings during an earthquake is obtained. These parameters are able to provide an inexpensive method for preparing a disaster program for an urban area. In this paper, the damage rate of different buildings in Shiraz City was obtained. In addition, the damage potential of the entire city area is calculated.