Abstract
Seismic hazard assessment in the Himalayan region remains highly uncertain due to the limited historical record and complex fault behaviour. To help address this, we present a 10,000-year long catalogue of synthetic earthquake ruptures on the Main Himalayan Thrust (MHT), one of the most hazardous continental fault systems on Earth. Simulations were performed by implementing geodetic models of the MHT’s geometry and slip rate into the physics-based Rate-and-State Earthquake Simulator (RSQSim), which applies the concepts of rate and state-dependent friction to generate long-duration synthetic earthquake catalogues. The MHT catalogue we generated reproduces key characteristics of observed seismicity, including magnitude-frequency distributions, rupture extents, and spatial patterns along the MHT. A key result is that low-coupling zones, previously inferred from geodetic data, consistently act as rupture barriers in the simulations, effectively limiting the maximum magnitude to Mw 8.9. In addition, we implemented this MHT RSQSim catalog into a stochastic probabilistic seismic hazard assessment (PSHA) of Nepal and compared the hazard estimates to a conventional PSHA model. At 10% probability of exceedance (PoE) in 50 years, the maximum difference (RSQSim derived hazard - classical PSHA) in Peak Ground Acceleration (PGA) range from +0.1g (+20%) to -0.6g (-70%), while at 2% PoE in 50 years the differences are +0.3g (+30%) to -0.6g (-40%), and at 0.5% PoE in 50 years, it is +0.4g (+30%) to -0.7g (-40%). In relative terms, 84% of sites have an absolute hazard difference below 60% at 10% PoE in 50 years, while 84 % of sites have an absolute hazard difference below 30% for 2% and 0.5% PoE in 50 years. Our results suggest that physics-based simulations offer a valuable complement to conventional source models, particularly for faults with variable rheologies and limited earthquake records like the MHT.