Measurement of the level of risk of land subsidence in No.18 urban residence area of Tehran

Land subsidence is considered as one of the geomorphic hazards which has a smooth and inward movement and in long term manifests its destructive effects. Occurrence of such a hazard can be an agent for formation and intensification of the vulnerability of human activity centres which are located on natural hazardous beds. In such situations، having a sufficient knowledge of the degree and level of vulnerability can provide sufficient time for planning and preparing a situation to alleviate risks and consequently easing crisis. For the measurement of the level of the risk of land subsidence in No. 18 urban residence area of Tehran، degree of land subsidence was analysed using satellite data and InSAR technics. The method being used to conduct this research is thorough-descriptive-analytical. For this to be achieved، different required data sources as well as thorough data was provided and after being digitised and processed was placed on the GIS environment to establish a local data base. In the next phase rate and slope of land subsidence was extracted using InSAR technic. Results from the process of radar images of PALSAR evaluator of ALOS satellite in 2009-2010 shows that land subsidence in No. 18 area and its neighbouring area follows a surface paradigm. Residential area’s map shows that a considerable section of this area’s houses are involved with land subsidence. Space of the whole area is estimated to be 380 hectare that 150 hectare (40%) of this space in three sections (1، 2، 3) is going through land subsidence with the rate of 1-25 cm. unexpected land subsidence and destruction and desolation of vulnerable structures in the studied area in which population density is high can be accompanied by death tolls and leads to a catastrophe. The most tragic situation for this area is that land subsidence happens with earthquake. Earthquake can be a trigger for land subsidence to happen in these areas. Predicting such a catastrophe in this area is not irrational because this area has the potential of quake being close to the active fault zone of Rey.