Measurement and evaluation of physical resilience of urban communities against earthquake (Case study: Tehran neighborhoods)

Introduction
In the recent years, the active institutions and agencies of accident reduction have focused more on the activities to achieve a community resilient against accidents. Earthquakes have a higher priority due to the fact that they inflict wider range of losses and widespread social abnormalities. In the past years, the world has seen some of the unpredicted natural accidents like Tsunami in Asia, Hurricane Katrina and Sichuan earthquake. Although some of the predicting devices are effective in reduction of the influences of the crises, the fact is that future accidents cannot be predicted based on the evidence. As a result, in order to prevent increase in vulnerabilities, it is necessary to know the level of the resilience of local communities as well as the capacity of the community for withstanding and recovering against the accidents in times of crisis.
Iran, due to its climactic and geological characteristics especially its location over Alps-Himalaya earthquake belt, is one of the most vulnerable countries of the world. The risk indicator of crisis by United Nations Development Program indicates that after Armenia, Iran is the most vulnerable against earthquakes, and 31 cases of all the 40 possible natural disasters have occurred in Iran.
Tehran megacity is in serious situation as a result of some factors. These factors are its location in a zone of high and very high seismic risk, failure to comply with safety rules like building in the privacy faults and the areas prone to geological instabilities, design and construction of inappropriate buildings and critical facilities with possible seismic intensity, no planning and required operational capabilities for disaster management for dealing with the consequences of an accident as well as the existence of multiple aging and vulnerable textures. For the same reason, it seems necessary to analyze the situation of Tehran from the point of physical and geographical features influential in time of accidents. Thus, this study aims to analyze the level of physical resilience in selected neighborhoods of Tehran by recognizing the indicators and factors influential on the physical resilience of urban communities. This study also wants to provide a framework to measure the level of the physical resilience in cities.
 
Methodology
The current article is applied research in the aim with a descriptive-analytic methodology. In this research, according to the question and the objective, the family was chosen as the unit of analysis. The sample size was calculated by Cochran formula to be 369 families, from the entire 2266984 families living in Tehran neighborhoods. In the next step, the neighborhoods of Tehran based on the social-economic status were divided into four classes (high, above average, below average, low).One neighborhood was selected from each class for the random sampling method. Then, based on the share of each class, sample families were systematically chosen from the sample neighborhoods. In this research, due to the lack of data about the issue a large amount of information was gathered about resilience based on library research (articles, books and reports). The dimensions and frameworks of resilience specified the indicators of physical resilience to be operationally defined. In the next step, using field study and questionnaire, the reliability was validated by pre-test; the needed data were gathered from the families of the sample neighborhoods. Then, the data of the questionnaire were entered into SPSS; the validity of the questionnaire was calculated by Cronbach, 0.835. This value shows its high coordination and sustainability. In the next step using SAW, the primary matrix of data was made. Then, using Electre method the level of physical resilience of studied neighborhood was measured.
 
Results and Discussion
Based on the results of the research, the weights of the factors are determined. The weight for building density index was 0.12, structural strength index 0.31, the indices of incompatible land uses and open spaces 0.11, availability index 0.1 and the index of ground features 0.25. Structural Strength Index and availability index have, respectively, the highest and the lowest priority, in comparison to indexes of physical resilience. Also, the results of the Electre model displayed that the level of physical resilience in target neighborhoods is different in their spatial distribution. According to total matrix and Electre model, it can be said that Gheytarie neighborhoods (A1), Satar Khan (A2), Narmak (A3) and Ghale Morghi (A4) were, in the best and worst situation from the view point of physical indexes.
 
Conclusion
Physical resilience is one of the effective dimensions on the level of resilience of communities through which the physical and geographical features of the community influential in time of accident can be assessed. In this research to measure and analyze the level of the physical resilience in chosen neighborhoods of Tehran, the indicator and factors influential on the level of resilience of communities were initially identified. To gather the required data from the studied neighborhoods, the indicators of physical resilience were categorized based on their priority by the experts using the process of hierarchical analysis. In the next step, using SAW the decision-making matrix was prepared. Finally, using the Electre method, the studied neighborhoods were prioritized based on their levels of physical resilience indicators. The results showed that these neighborhoods, from the view point of physical resilience, are in different levels. Gheitariye, Satar Khanm Narmak and Ghale Morghi neighborhoods were in a spectrum of the best to the worst situation. Also, the framework provided in this research can be applied to other neighborhoods for a measurement and analysis of the physical resilience level. Some suggestions for the improvements of the resilience in studied neighborhoods are presented: Management and organization to prepare effective action in order to reduce the dangers of natural accidents and create a unified crisis command; Study on the vulnerability level of neighborhoods in time of crisis, especially earthquake to prepare the vulnerability maps of neighborhoods; Increase in the cooperation of people and their preparation for confronting the critical times.