An Analysis of the effect of Tehran's Spatial Expansion in Increasing Earthquake Vulnerability (Time Period: The Last 200 Years)

Tehran as the biggest metropolitan of Iran is located in the areas that are at high-risk of earthquake. What increases Tehran''s vulnerability toward earthquake is the urban physical expansion in vaious dimensions. Since the analysis of the mentioned expansion is a solution to many urban problems، the effects of Tehran expansion in increasing vulnerability to earthquake has been surveyed in last 200 years. The purposes of this study include: 1) to represent Tehran physical expansion in the last 200 years. 2) To explain the relationship between population increase and Tehran expansion. 3) To analyzed Tehran spatial expansion with regard to earthquake vulnerability. In this study we review the physical expansion of Tehran from the time that it has been a small village to the time that it changed to a metropolitan. The population and surface area data of Tehran are collected in the duration of 1786 – 2009 using Holdren model، in order to explain the relationship between urban population growth and its expansion. With regard to the historical earthquake records، earthquake seismicity background and various faults، findings show that Tehran is at high risk of earthquake vulnerability. In the period of study، 91 percent of Tehran expansion was due to population growth and 9 percent of Tehran expansion has been related to sprawl and horizontal growth. Uncoordinated and unprincipled expansion of Tehran، especially in recent decades، construction near active faults show that if a severe earthquake in Tehran happen، it makes loss and damage to this city.