The present study has been conducted to evaluate the vulnerability of urban spaces to earthquake hazard using the catastrophe theory in the context of geographic information system. In the evaluation method based on the catastrophe theory, the importance of each criterion is calculated using the internal mechanism of system, so subjectivism resulted from decision makers' judgment decreases. This methodology was applied to assess seismic vulnerability of Tabriz city. During recent decades, this city has developed spatially. Space limitation has caused the development of the city in hazardous locations including the proximity to the Tabriz fault. Considering the seismic potential of the great Tabriz fault and construction density adjacent to this fault, one can say that earthquake is the most important and serious natural hazard in the city. In the current study, important natural, physical, and human variables affecting the level of vulnerability were combined using fuzzy functions of the catastrophe theory. The results indicate the efficiency of this model in seismic microzonation of urban spaces. Results of the seismic microzonation of Tabriz using this model are consistent with field facts. According to the results obtained, a considerable part of the city's built-up lands (more than 35 percent) is located in the high seismic vulnerability class. Due to the effect of a set of variables such as proximity to the great Tabriz fault, steep slopes, unstable geological formations, marginalization, and high population density and floor area ratio, the vulnerability in parts of the north of the city is very high.
