Contribution of seasonal hydrological loading in the variation of seismicity and geodetic deformation in Garhwal region of Northwest Himalaya

Abstract

The study interprets the effect of seasonal (pre-, co- and post-monsoon) hydrological loading due to the Ganga river basin over the seismicity and geodetic deformation in the Garhwal Himalayan region. Geodetic data from six cGPS sites are used, three sites out of six are established in the Himalayan region, one is located in the Ganga basin and two sites are located in the Indian shield. First, we estimated the average seasonal variation in GRACE-derived TWS of entire India for the period of 2002–2016. It is observed the seasonal effect over TWS (Terrestrial Water Storage) due to hydrological fluctuations in the Indo-Gangetic Plain (IGP). It has also been noticed that the geodetic velocities for both the North and East components are more in pre-monsoon than post-monsoonal season. Whereas the vertical component in cGPS sites of Himalaya (DEHR and MAND) agrees to the hypothesis of upliftment during post-monsoon and subsidence in pre-monsoon. TWS mass change is detected high during the co-monsoon (2.32 × 104 km3) and it is observed low −2.22 × 104 km3 (in pre-) and −8.13 × 103 km3 (in post-) monsoon seasons respectively. GPS measured horizontal displacement agrees with seasonal loading but it contains some anomalous behaviour, which may be the result of surface hydrological mass movement or the effect of the Gorkha earthquake, 2015, however an inverse relation between vertical geodetic displacement and loading have been observed. The average strain rate values over cGPS sites during 2016–2018, are more negative in post-monsoon than in pre-monsoon which means that plate movement is highly compressional. We have also inferred a significant role of loading over the seismicity and linear strain rate, which increases with decreasing hydrological loading in the Ganga river basin and vice versa.