Assessment and Zoning of Bojnord City in Terms of Seismic Hazards

Abstract

The unstable tectonic conditions contribute to the occurrence of major seismic activities in Iran each year so that this country is known as a geographic area vulnerable to incidents. This article is aimed at evaluating and zoning the city of Bojnord in terms of seismic hazard and vulnerability. This is an applied research with a descriptive–analytical method. A library-documentary method along with comparison of topographic maps with present condition was adopted for data collection. The spatial and non-spatial (descriptive) data were assessed using ArcGIS and Expert Choices models and software, hierarchical analysis, weighting, and then they were analyzed by determining the effect of layers involved in the zoning. The research area, Bojnord city, was divided and zoned into 15 districts according to five indices of microlithic, area, accessibility, population and enclosure. In order to determine the final indicator for the vulnerability of the districts, seven indicators of archaism, materials, number of floors, passages width, enclosure, microlithic and land use were adopted. Indices were weighed by AHP; and after computing the weight of each layer in the GIS using the Spatial Analysis and the Weighted Overlay function, the weights obtained from the ANP model were assigned to each layer, and the layers were overlaid to plot the vulnerability map of the city. The results suggested that districts 3, 11 and 12 were most vulnerable to seismic hazard due to decrepit and worn-out texture. A total of 27% of the urban areas were subject to severe and relatively severe seismic hazard. Also, 53.3% of the 15 districts of Bojnord were in poor and relatively poor conditions with respect to indices under study. In the end, strategies for alleviating vulnerability and improving urban districts are proposed. Buildings with high level of enclosure, low-quality materials and high building density have amplified vulnerability compared to other areas. Compact texture, insufficient open spaces and worn-out tissues have deteriorated their vulnerability. Further, distance of urban areas from the relief centers, narrow passageways and thus the possibility of blockage and high enclosure can prolong the travel time and slow down rescue operations.