Heterogeneous Seasonal Deformation and Strain Budget in Himachal, NW Himalaya from new cGPS measurements: Hydrological and Seismic Hazard Implications

GPS measurements from 10 new permanent sites installed in Himachal, NW Himalaya are analysed with the primary objective to decipher the seasonal crustal deformation characteristics, its origins and hydrological implications. Additionally, we focus on the seismic hazard implications of the seasonal transients as well as of the long-term secular motion of GPS sites. Our findings suggest that the global hydrological loading models can relatively well explain the temporal surface displacements resulting from the monsoon rainfall in the Indo-Gangetic plains (IGP) but poorly account for the winter snowfall in Higher Himalaya. The approximately elliptical horizontal seasonal motion of GPS sites seems to be controlled by the spatio-temporal variations in the monsoonal hydrological load over the IGP. The hydrological process derived from the GPS data suggests slow and steady recovery in the water storage in Himachal Himalaya. The more intriguing phenomena is reflected in the unusually high seasonal site uplift and the yearlong (mid-2020 – mid-2021) plunge in the water storage corresponding to the time-period of COVID-19 lockdown phases, which could be speculated as its indirect impact on the crustal deformation history. The seasonal strain analysis revealed significant spatial heterogeneity. The arc-normal and arc-parallel seasonal strain resulting from differential seasonal motion between GPS sites seems to be primarily localized in the vicinity of locking transition zone, while the locked segment is being largely translated without experiencing significant strain. The localized seasonal strain showed positive correlation with the background seismicity rate suggesting possible modulation of the earthquake nucleation process. The regional seismic hazard assessment suggests susceptibility to a future great earthquake of ∼Mw8.4. The additional observed equivalency between the updated strain budget (∼9.3 m) and the previously reported co-seismic displacement (∼9.3 m) during the last great earthquake around ∼1400–1500 CE, suggests a recurrence interval of ∼600 years for great earthquake events in Himachal Himalaya with significant reliability.