[G01-P] Poster

[G01-P-06] Developing a semi-dynamic datum for Nepal after the April 25 Gorka Earthquake

Christopher Pearson¹, Niraj Manandhar², ^○Paul Denys¹ (1.School of Surveying University of Otago, 2.Survey Department of Nepal)

Along with the damage to buildings and infrastructure, the April 25, 2015 Mw7.8 Gorkha earthquake caused significant deformation over a large area in central Nepal, with displacements of over 2 m recorded in the vicinity of Kathmandu. In order to correct the resulting distortions in the geodetic reference system, Nepal is in the process of introducing a new semi-dynamic datum that is aligned with ITRF2014 (epoch 2016.0). The new geodetic datum will incorporate a national deformation mode (NDM) that will have the capacity to correct for earthquake displacements as well as ongoing tectonic deformation associated with Nepal's location on the India/Eurasian plate boundary. The NDM discussed here contains models of the velocity field and both co-seismic and post seismic deformation for the Gorka earthquake plus co-seismic deformation for the Mw 7.3 12 May Aftershock. The velocity model for Nepal is based on a compilation of published velocity measurements from previous studies for Nepal and adjacent regions of China and India combined with new velocity estimates for the Nepal GNSS array stations. We have developed a preliminary velocity field by combining these studies and aligning them with the published ITRF2014 velocities for IGS stations. The co-seismic deformation associated with the Gorkha earthquake and its 12th May Mw7.3 aftershock are modelled using published dislocation models. In order to estimate the post-seismic relaxation, we used an exponential function with a uniform 43 day time constant. The model is implemented as a series of grid files allowing the secular velocities, co-seismic displacements for the April 25, 2015 Mw7.8 Gorkha earthquake and the 12th May Mw7.3 aftershock and the post-seismic relaxation coefficients for the Gorkha earthquake to be estimated. Using these grid files it is possible to estimate the deformation as a function of time for any point in Nepal and correct both survey measurements and coordinates to a common reference epoch.