Evaluating the vulnerability of urban buildings to various earthquake intensities Case study: District 9 of Tehran Municipality

The rapidity of urbanization, especially in developing countries, has led to the fact that half of the world’s population is currently settled in urban areas. Most of these areas with high population density are vulnerable to crises (Shelter Center, 2010: xiv). The fact is that the increase in the concentration of physical capital, infrastructure and economic activities in the cities has led to the increase in adverse effects of natural disasters (Tangri et al., 2008: 30; Lall and Deichmann, 2012). Meanwhile, it has long been argued that the earthquake, as one of the most catastrophic and devastating types of natural hazards, especially in developing countries (Dong & Shan, 2013: 85)has caused lots of damages to the properties and assets in urban areas and around them, through the destruction of urban buildings and infrastructure, (Min et al, 2010). Like other developing countries, Iran has experienced a high level of urbanization that has completely changed the physical structure of urban areas (Soltani et al., 2011: 6644), so that by 2015, the urban population of the country has been 74.3 percent, which is estimated to reach 91.5 in 2050 (Statistical Yearbook for Asia and the Pacific, 2015). Increasing urbanization in the cities of the country along with unplanned development is one of the factors that boost the possibility of increasing casualties and damagesdue to the occurrence of natural disasters in the cities of the country (Pourmusavi, 1391: 40) and leads to the loss of resources and achievements whose reestablishment will take many years (Patterson et al, 2010: 128). The present research is of applied type with descriptive-analytical method. Thestatistical population is the buildings of district 9 of Tehran municipality. Tocomplete the library informationin order to understand the status quo, the studies and deductions of the Information Technology and Communication Organization of Tehran Municipality updated in 2015 were used. The indices used in the research have been weighted based on the experts’ opinions using the Analytic Network Process (ANP), and the obtained results have been applied on the layers under study in the GIS environment and the map of each layer has been prepared in the Geographic Information System.Finally, the general vulnerability map of the region was extracted through the integration of the layers under study (overlay). The opinions of the experts are determinant in evaluating thevulnerability of the city, butin this research, in order to reach a precise evaluation, along with the preparation of the map based on the experts’ opinions, the vulnerability scenario has been developed at different intensities, thereby to standardize the data, and to analyze the layers and criteria, the fuzzy model andthe linear threshold function have been used, respectively. The results have been categorized into 5 vulnerability groups of very low, low, medium, high and very high, and the percentage of each group has been calculated. Tools used in the research are SUPER DECISION and GIS. The present research was carried out aiming at vulnerability evaluation of urban buildings in district 9 of Tehran municipality to various intensities of earthquake, thus, in this research, the vulnerability rate of urban buildings to various earthquake intensities was measured using ten indices (type of material, type of view, building density, age of the building, number of floors, ground area of  buildings, compatibility of neighboring uses, distance from fault, geological formations and the width of passages)along with the required sub criteria. To design the earthquake scenarios at different intensities, the first step was to accomplish stratification for each of the main criteria and sub criteria using the weights obtained from the ANP in the Arc GIS environment, then, the general vulnerability map of the region was prepared by overlaying the layers. Finally, the earthquake scenarios at different intensities were designed by fuzzification of the map. In order to determine the seismicity potential of the study area which is part of the primary and very important stepsin the process of the determination of vulnerability levels of various regions to earthquake, the preparation of the major faults’ map of the region, the preparation of the earthquakes epicenter map, the determination of the intensity and magnitude of earthquakes, the estimation of the features of earthquakes that are likely to occur by the significant faults of the study area were placed on the agenda. For this purpose, in order to evaluate the vulnerability of earthquake hazard, 10 indices were investigated as the effective factors on the vulnerability of urban buildings which have been selected based on the indices of previous studies. These indices (type of material, type of view, building density, age of the building, number of floors, ground area of buildings, compatibility of neighboring uses, distance from fault, geological formations and the width of passages) were analyzed using the ANP calculation method whichhad beenscored by the experts, and the weight of criteriawas applied to the effective layers of the vulnerability, and finally, the general vulnerability map was extracted by integrating the layers in the GIS environment. In order to evaluate the vulnerability rate of urban buildings, the data obtained from the ANP model was fuzzified, and the earthquake scenarios were ultimately designed based on the seismicity potential of Tehran faults and were applied on the general vulnerability map of the study area. The results of the research indicate that in an earthquake with a modified intensity of 6 mercalli, the vulnerability rate of urban buildings in the vulnerability ranges of very low, low, medium, high and very high are 26%, 56%, 17%, 1% and 0%, respectively and the damaged buildings in the districts 1 and 2 are in the vulnerability ranges of very low (28% & 24%), low (53% & 59%), medium (18% & 16%), high (1% & 1%) and very high (0%). In an earthquake with a modified intensity of 7mercalli, the vulnerability rate of urban buildings in the vulnerability ranges of very low, low, medium, high and very high are 21%, 10%, 52%, 16% and 1%, respectively, and the damaged buildings in the districts 1 and 2 are in the vulnerability ranges of very low (23% & 18%), low (11% & 9%), medium (48% & 56%), high (17% & 16%) and very high (1% & 1%). In an earthquake with modified intensity of 8mercalli, the vulnerability rate of urban buildings in the vulnerability ranges of very low, low, medium, high and very high are 7%, 4%, 10%, 61% and 18%, respectively.