Crustal deformation and strain analysis in Nepal from GPS time-series measurement and modeling by ARMA method

High-precision Global Positioning System (GPS) measurements from 2002 to 2017 in Nepal has been analyzed and modeled with Autoregressive Moving Average (ARMA) method. The measured velocities of the GPS sites in ITRF-2014 indicate 6-12mm/year N-S convergence inside the Nepal between India and Tibet. This convergence occurs in the southern and western border of Nepal, but it is negligible to the eastern border of Nepal. ARMA-modeled result of India-fixed velocities is able to successfully model (within 0.5mm/year) the current measured velocities in Nepal. Synthetic or modeled velocities using ARMA method and measured velocity have difference2mm/year at some sites. This indicates the possibility of very small level of a ductile deformation. In the present best-fit ARMA model, the modeled velocities8-10mm/year convergence taken up from northern to southern boundaries of Nepal indicates slip along active Main Himalayan Thrust (MHT) which is the cause of change in tectonic strain and may be able to trigger earthquakes inside the country. Dislocation modeling of active MHT is also carried out in the study using GPS vertical displacement. The geometric model of the MHT is characterized by a rectangular plane with dip angle of 9.5 degrees and the reverse kinematics with a slip of 19mm/year. The thrust is located at a depth of 20km. In addition, the regional deformation of the Nepal has been checked by baseline measurement and coordinate stability of GPS sites for the different zones. The baseline divergence and convergence of nearest GPS sites have been tested using triangular sites. The summary of regional deformation implies N-S convergence only and rules out any type of E-W convergence. Finally, the investigation of observed and modeled strain confirms that there is no significant strain accumulation due to localized regional deformation or earthquakes specific to the active dislocations and faults. This suggests that the convergence from northern to southern boundaries of Nepal is associated with the slip along the MHT only.