The seismic vulnerability assessment of Housing of Tabriz (Case Study: District 10 )

Natural hazards, with various types and extent, as recurring and destructive phenomena, have always existed throughout the life of the planet and have always been a serious threat to humans since the creation of mankind (Rajabi et al., 2018: 184). Among the natural hazards, earthquake is one of the most horrible ones in the history of mankind, which belongs in the category of immediate dangers. This natural phenomenon can be characterized by their high destructive potential and the brutal killing in a short time (Taghipour, 2016: 195).There are many definitions of vulnerability in the literature. Vulnerability is defined as “a state combining physical, economic and environmental factors, which increases system sensibility to danger” by the United Nations/International Strategy for Disaster Reduction (Peng, 2012: 95). One of the most effective strategies to reduce social and economic losses resulted from earthquakes is to mitigate the vulnerability of society to seismic hazards based on an accurate and scientific risk assessment (Wei et al., 2017: 1289). It is not possible to accurately predict the earthquake, but the earthquake can be studied from the following two aspects, so the casualties caused by the earthquake decrease as much as possible. First, seismic vulnerability should be assessed before the earthquake, and the construction of disaster prevention and reduction system should be strengthened in the regions with relative high vulnerability of population. Second, according to the estimated casualties, the reasonable rescue measures would be deployed to carry out the effective rescue (Zhang et al., 2018: 2).

In the present study, the seismic vulnerability of district 10 of Tabriz due to its proximity to Tabriz fault has been assessed. District 10 is one of the northern areas of the city and its texture is mainly marginal, which increases the vulnerability to earthquake. Various factors affect the vulnerability of an urban area to earthquake including height and age of the buildings, the quality of materials, population density and distance to active faults (Khamespanah et al., 2016: 58). In the present study, 12 factor were applied to investigate the seismic vulnerability of district 10 of Tabriz metropolis: slope, distance to fault, to hazardous installations, to the hospitals and fire stations, population density, residential density, access to open urban public spaces, number of building floors, building quality, materials and urban grain.In order to present the vulnerability map of district 10, thematic layers of the studied criteria were prepared and transformed into fuzzy. Decreasing and increasing linear functions were used to fuzzification the thematic layers. The five fuzzy operators i.e. and, or, product, sum and gamma can be used for combining thematic maps. The operator used in this study to integrate a fuzzy subject layer is the gamma operator. Also, the vulnerability coefficient of district 10 to the average earthquake intensity was calculated. The range of numbers obtained from the vulnerability coefficient is between 0 and 1, indicating lack of damage and a building collapse, respectively. (Ahadnezhad Reveshti et al., 2010: 182).

In order to assess the seismic vulnerability, it is necessary to generate a seismic micro zonation map for the study area. To this end, 3 steps were performed as follows:Thematic layers affecting seismic vulnerability were prepared in the GIS environment and their spatial distribution in the district 10 of Tabriz was evaluated.In this step, thematic layers were transformed into fuzzy using fuzzy functions.Fuzzy thematic layers were combined using a fuzzy operator and a seismic vulnerability map was prepared for district 10 of Tabriz.The results of seismic zoning of region 10 of Tabriz using fuzzy logic can be summarized as follows: - About 4.5% of the study area is in a very high vulnerability and 12.6% of its area is in a high vulnerability class. Also, the total area of ​​low and very low vulnerability zones is about 64.9%. Very low vulnerable areas correspond to the barren lands, green spaces and all open spaces of the district. In addition, in Eram neighborhoods in the north of the study area, residential and population density are much lower than others. Some of the southern neighborhoods of this region, such as Sheshgalan and Daveh Chi, are less vulnerable to earthquakes due to the lower population and residential density, proximity to the hospital, to green spaces and less distance to the fire station. . Neighborhoods such as Khalilabad and Ghorbani in the central parts of district 10, are among the most vulnerable ones to earthquakes. Factors such as high population and residential density, lack of access to urban open spaces are the most important reasons for the high vulnerability of these areas. The central neighborhoods of district 10 are the most vulnerable to earthquake hazard. Due to the high population density in these areas, a large earthquake can lead to severe damage and loss of life in these areas. The results of damage analysis in district 10 of Tabriz, considering a possible earthquake with a magnitude of 10, show that the northern and southern parts of region 10 are in class D0 against a possible earthquake and will be without damage. About 6.4% of urban spaces in the study area are in Class D3, which will suffer significant to severe damage. Finally, about 0.6% of urban spaces in the study area are in class D5. This class includes part of the central neighborhoods and indicates the very high vulnerability of these areas to an earthquake.

Findings show that vulnerability is higher in the central neighborhoods of district 10. Factors such as high residential and population density, old tissue, distance to hospitals and lack of access to public open spaces are the most important factors that cause very high seismic vulnerability in this part of the city. District 10 of Tabriz is located near the large north fault of Tabriz and in this regard, the whole area is vulnerable to earthquake. However, proximity to the fault alone cannot be a measure of the vulnerability of urban buildings and structures, but planning and physical factors in the city can aggravate or, conversely, reduce seismic vulnerability. The results of the seismic vulnerability coefficient of the study area to a possible earthquake with a magnitude of 10 show that the buildings located in the central neighborhoods of district 10 have the highest seismic vulnerability. Due to the high population and residential density in these areas, during an earthquake there will undoubtedly be very high and catastrophic casualties and financial losses.