On interseismic elevation changes and strain accumulation for great thrust earthquakes in the Nepal Himalaya

Abstract

Estimates of interseismic ground elevation change rates from Nepal Himalaya based on repeat levelling observations between 1977 and 1990 in the meizoseismal zone of the great thrust earthquake of 1934 have been reported by Jackson and Bilham [1994]. We explain them using the model of Savage [1983] for seismic strain accumulation and release along plate boundary faults (PBF) at convergent plate margins. Thus the section of the PBF under the Nepal Himalaya that ruptured during the 1934 earthquake may be currently locked and the hanging wall rocks may be experiencing downdip drag at the local plate convergence rate. Three independent estimates of 150, 100 and 50 km for downdip rupture width during the 1934 earthquake are available. If we use them as estimates of the current width of the locked zone in Nepal, then values of 18, 14 and 12 mm/year respectively for the plate convergence rate are obtained. Although all these values compare favourably with the estimated long term average rate of 18±7 mm/year for plate convergence accommodated at the Himalaya, the rms error is the least for the model with 150 km width of the locked zone.