Study of subsidence in Gorgan using InSAR method

In recent years, land subsidence creates a serious environmental disaster in various places of the Iran. Land subsidence is a geomorphic phenomenon that caused by several factors; sometimes it is influenced by natural factors but in many cases occurs due to human intervention specially uncontrolled exploitation of groundwater from aquifers. There are several methods to measure the land subsidence including the use of GPS (Global Positioning System), the precise leveling and remote sensing techniques, particularly Interferometric Synthetic Aperture RADAR (InSAR) method. Between these methods, the InSAR technique is the sufficient method for ground surface deformations. In this research, the land subsidence phenomenon in Gorgan has been investigated by the InSAR technique using ENVISAT radar images. Gorgan is the capital of Golestan province in Northeast of Iran. The tectonic situation of the studied area is very complex; this area is located between the uplifting Kopeh-Dagh belt to the West, subsiding South Caspian region to the east and uplifting Alborz mountain range to the South. The results show that the north of Gorgan has experienced subsidence in the period of 2007/01/26 to 2009/12/11 (34 months and 15 days). The subsided area has almost east–west trend which is consistent with the trend of tectonic structures. The amount of displacement is calculated about 4.8 cm. The graphs of the rainfall and groundwater level changes with time in Gorgan for the period of 2007/01/26 to 2009/12//11 show a downward trend, despite of seasonal fluctuations. The consequences of this decline in groundwater levels may lead to land subsidence in the study area.