Locking degree and slip rate deficit distribution on MHT fault before 2015 Nepal Mw 7.9 earthquake

Abstract

The spatial pattern and rate of strain accumulation on a fault during the pre- and inter-seismic phases are very important for interpreting the mechanism of earthquakes and evaluating seismic potentials. Here we use global positioning system (GPS) data and the block-dislocation model to invert for the locking degree and slip rate deficit of the Main Himalayan Thrust (MHT) fault in the southern margin of Tibet before the 2015 Mw 7.9 Nepal earthquake. Results show that the locking depth and slip rate deficit increase from the west to the east. Along the western segment of the MHT fault (80°E–84°E), the locking depth is estimated to be 12–17km with a slip rate deficit of 0–5mm/a; along the central Nepal segment (84°E–87°E), the locking depth is 16–21km with a slip rate deficit of 6–10mm/a, whilst along the eastern segment (87°E–90°E), the locking depth increases to 23–26km with a slip rate deficit of 8–13mm/a. The 2015 Nepal earthquake initiated at the boundary between the western and central segments, an area with as where the slip rate deficit varies dramatically from 0 to 9mm/a within 50km resulting in high energy gradients. High strain concentration along the central and eastern segments leads to unilateral propagation of the rupture to the east. Given the paucity of large seismic events over the previous decades and the current high slip rate deficit, seismic hazard on the eastern Nepal segment remains high.