Analyzing the Land Subsidence activity in the Joshimath Region of Indian Himalayas Using Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR)

Abstract

 The Himalayan region is prone to natural disasters, including land deformation caused by tectonic activity, earthquakes, landslides, and human activities such as construction of large infrastructural projects. In the Joshimath region, located at the base of Middle Himalayas, there has been a significant number of reported cases of visible deformation in roads and buildings over the past six months i.e. between July 2022 to December 2022, with 610 buildings, including houses and hotels etc., showing cracks in their walls and foundations. This poses a danger to both the community and infrastructure in the area. To study this deformation, time-series synthetic aperture radar interferometry was used to monitor land subsidence in the region. An analysis of land subsidence in the entire Joshimath region was conducted using Time-Series Synthetic Aperture Radar Interferometry, and the land deformation velocity for was calculated using a PsInSAR approach, which measured the displacement velocity in mm/year. The results indicated that the rate of displacement, measured in Line of Sight (LOS) deformation velocity, was in the range of +187.55 mm/year to -84.65 mm/year. A positive sign indicates movement away from the SAR sensor, while a negative sign represents movement towards the sensor. The highest rate of subsidence was observed in the northwest region of the Joshimath that is in the range +103.22 mm/year to +187.55 mm/year, while areas in the north and central region also experienced high to moderate subsidence of +63.73 mm/year to +103.22 mm/year. In contrast, the southwest region was found to have experienced expansion measuring −84.65 mm/year to -13.13 mm/year. Additionally, the southeast region of the town had a rapid land subsidence ranging from -13.13 mm/year to -5 mm/year towards the lower part of the town. The potential causes of deformation in the Joshimath region are believed to include an inadequate drainage system in the town, high levels of erosion caused by the Alaknanada river, which is impacting the stability of the slope on which the town is situated, and recent development of large infrastructure projects in this disaster-prone area, that include construction of a hydropower project tunnel by NTPC and the expansion of the Chardham Highway. The fact that the ridge on which the town sits is composed of debris from past landslides further exacerbates these issues, as the terrain formed by such debris has a lower bearing capacity, making it a poor foundation for heavy infrastructure development.