Evaluating the seismic potential of megacities in Iran

Iran is one of the countries that is prone to natural hazards due to its geographical situation. One of the risks that has always threatened Iran is the risk of earthquakes. The land of Iran, as a part of the active tectonic zone of the Alps-Himalayas, has been affected by many tectonic activities over time, such as the appearance of the Zagros-Makran and Alborz-Kope Dagh mountain ranges in the Iranian plateau as a result of subduction of the Arabian plates. The Indian Ocean is one of the landforms resulting from this convergence. According to the geological situation of the Iranian plateau, this plateau is facing many disturbances and this problem has caused Iran to be one of the earthquake-prone countries in the world. Earthquake is the most important natural hazard that is always associated with a lot of human and financial losses. Due to its unpredictability and its power, this hazard has faced serious challenges in the seismic regions of the world. In fact, large earthquakes are one of the most destructive natural disasters, which often lead to widespread casualties and many deaths, and many cities are vulnerable to large earthquakes. Among the areas that are vulnerable to the risk of earthquakes are the metropolises because they house a large part of the country's population. According to the statistics of 2015, the metropolitan cities of Tehran, Mashhad, Isfahan, Karaj, Shiraz, Tabriz, Qom, Ahvaz and Kermanshah include about 27% of the country's population. Due to the importance of the subject, in this research, the seismic status of Iran's metropolises has been evaluated.

In this research, information related to the epicenter of earthquakes recorded in Iran during the years 1286 to 1402 (1907 to 2023), demographic information of Iranian metropolises, statistical information related to the state of constructions of metropolises, and also The information obtained from satellite images has been used as the most important research data. The most important research tools are ArcGIS (to prepare the required maps) and SPSS (to analyze the data). Also, in this research, the Analytical Hierarchy (AHP) model was used in order to weight the parameters. According to the desired goals, this research has been done in two general stages. In the first stage, a 100 km boundary is defined for each metropolis, and then the earthquakes that occurred in this area are identified. In the following, the earthquakes that occurred in metropolitan areas have been analyzed in terms of number and size. In the second stage, based on 6 parameters, the state of vulnerability of metropolises has been evaluated. After evaluating the metropolises in terms of the desired parameters, first the parameters were normalized and then the parameters were weighted using the AHP model.

The results of the evaluation of earthquakes that occurred in the outskirts of 100 kilometers of metropolises have shown that the largest number of earthquakes with 390 recorded cases was related to the outskirts of Shiraz metropolis, and Isfahan and Qom metropolises recorded 19 and 20 respectively. Have the least number of earthquakes. Also, the results of the survey of the number of earthquakes with a magnitude greater than 6 on the Richter scale have shown that the outskirts of the metropolises of Shiraz and Kermanshah had the largest number of earthquakes with 4 earthquakes, and the outskirts of the metropolises of Isfahan and Ahvaz There has been no earthquake with a magnitude greater than 6 on the Richter scale. Considering that in addition to earthquakes, other factors are also effective in determining the vulnerability of metropolises against earthquake hazards, in this study, population parameters, population density, percentage of open space and percentage of worn-out fabric are also used. Has been According to the results, the largest population was related to Tehran city. The highest population density was related to the city of Mashhad. The highest percentage of worn out fabric was related to the city of Tehran and the lowest percentage of open space was related to the city of Tehran.

The results of this research have shown that Iran's metropolises have different seismic potentials due to their geo-structural position, and also, under the influence of various population factors and constructions, different potentials in terms of damage. They are resistant to earthquakes. In this research, in order to investigate the seismic status of metropolises, the earthquakes that occurred within 100 kilometers of them have been analyzed. According to the results, during the years 1286 to 1402, 999 earthquakes with a magnitude of more than 3 on the Richter scale occurred within a radius of 100 km from these metropolises, 15 of which had a magnitude of more than 6 on the Richter scale. Is. The results of the analysis of earthquakes have shown that the largest number of earthquakes occurred in the metropolitan areas of Shiraz, Ahvaz and Kermanshah, so that 390, 186 and 147 earthquakes occurred in these metropolitan areas, respectively. The lowest number of earthquakes with 19 and 20 cases respectively was related to the metropolitan areas of Isfahan and Qom. Also, the largest number of earthquakes with a magnitude greater than 6 on the Richter scale was related to the metropolitan areas of Shiraz and Kermanshah. The results of this section have shown that the seismic status of Iran's metropolises has been very different, and considering that in addition to the number of earthquakes, various human parameters are also effective in the degree of vulnerability to earthquakes, in this research Based on different parameters, the state of vulnerability of metropolises was evaluated. Based on the results, Shiraz metropolis with a total score of 17.68 is considered the most vulnerable metropolis in the country against earthquake risk. After this metropolis, Kermanshah and Tehran metropolises have the highest vulnerability potential with 13.12 and 10.87 points, respectively. Also, Isfahan metropolis with a total of 2.75 points has the lowest vulnerability potential among the metropolises of the country, and after that, Ahvaz and Qom metropolises have the lowest with 5.72 and 6.66 points, respectively. They are potential vulnerabilities.