The Indian Space Research Organisation (ISRO) and NASA (National Aeronautics Space Administration) of the US has jointly developed a forthcoming satellite named NISAR (NASA-ISRO-Synthetic-Aperture-Radar) which will help in mapping the most earthquake prone regions in the Himalayas with unprecedented regularity.
The data generated will be instrumental in generating advanced potential warning of land subsidence which was recently observed in Joshimath (Uttarakhand).
According to Dr. Prakash Chauhan, director of ISRO National Remote Sensing Center, the NISAR satellite expected to cost approximately $900 crores (with ISRO contributing one tenth) will use two bands-L band and S-Band to image the seismically active Himalayan Regions, every 12 days and create a deformation map.
The geo-science community can use this data to determine how strain is building up in various parts of Himalayas. The two frequency bands will provide a high resolution and all-weather data to from the satellite to that is expected to follow a sun-synchronous orbit and will be launched in January 2024.
In geology, strain refers to the deformations that occurs in rocks when it is under pressure from other rocks. This happens due to movement of continental and tectonic plates that are sliding, colliding, or subducting against each other.
The perfect example is the creation of the Himalayas. When the Indian Plate collided with the Eurasian Tectonic Plate, resulted in the formation of the Himalayas and it incrementally pushes upwards.
Based on the intensity of the past earthquakes, the knowledge of speed at which the plates move, and the locations where the plates interact (faults) can help geologists and seismologists in finding out regions that are most vulnerable to earthquakes and can predict the spread of the tremors.
However, one crucial factor called timing cannot be deduced. The Ground Based observatories can record and can pick up underground waves that result from an earthquake and provide early warning.
In 2021, scientists from the Geological Survey of India (GSI) published a strain map of the Himalayas with the help of 1252 GPS Stations and identified certain regions where greatest odds of generating earthquakes above 8 on the Richter Scale and their extent.
While satellite imagery to study deformation in land is already employed, the frequency and clarity of the images are critical. V K Gahalaut of the National Geophysical Research Institute (NGRI) said- “With a frequency of 12 days and the ability to be able to provide images even under cloudy conditions, NISAR would be a valuable tool to study deformation patterns, such as in Joshimath”.
Land Subsidence or the loosening of the sub surface had caused the several parts of Uttarakhand to sink and this caused water to seep via cracks and crevices into houses”.
In 2021, a large landslide of rock and ice triggered a flood in Chamoli, Uttarakhand that claimed close to 200 lives and additionally destroyed two hydropower projects.
It was the Satellite imagery that helped scientists decipher the cause of the flash floods.