Characteriztion of Effective Parameters of Land Subsidence in Tehran-Karaj Plain

Land subsidence is a global problem occurring as a result of various reasons including excessive groundwater extraction. In Iran, over 300 plains are suffering from this phenomenon and the rate of land subsidence in some plains is critical. Tehran city, as the capital of Iran, is located in Tehran-Karaj plain, therefore, the occurrence of land subsidence in this plain can be crucial. Hence, using InSAR method, the paper focused on reconnaissance and evaluation of factors such as; rate of the land subsidence, cause of land subsidence and the time delay. The maximum cumulative value of land subsidence in southwest of Tehran city for a 15-year period of time, from 2004 to 2018, was measured to be 1.94 m which is high and remarkable. The paper further presents the influence of five parameters including; alluvial thickness, natural frequency of earth, land use, geology, and soil granulation on land subsidence. The results of this study showed that land use, geology and soil granulation are also effective parameters on land subsidence, beside groundwater extraction in the study area. Moreover, the time delay between groundwater extraction and land subsidence was determined by comparing the time of sudden decrease in groundwater level and the instant of the land subsidence. In addition, a time delay zonation map was presented for the study area. This map can be helpful in design and construction of geotechnical projects, such as subway tunnels, railways, roads, airports, etc., in the study area.