Seismogenic potential of the Main Himalayan Thrust constrained by coupling segmentation and earthquake scaling

Recent studies have shown that the Himalayan region is under the threat of earthquakes of magnitude 9 or larger. These estimates are based on comparisons of the geodetically inferred moment deficit rate with the seismicity of the region. However, these studies do not account for the physics of fault slip, specifically the influence of frictional barriers on earthquake rupture dynamics, which controls the extent and therefore the magnitude of large earthquakes. Here, we propose a methodology for incorporating outcomes of physics-based earthquake cycle models into hazard estimates. The methodology takes also into account the moment deficit rate, the magnitude-frequency of the current and historical catalogs, and the moment-area earthquake scaling law.

For the Himalaya setting, we estimate an improved probabilistic estimate moment deficit rate using coupling estimates inferred using a Bayesian framework. The locking distribution of the fault suggests an along-strike segmentation of the MHT with three segments that may act as aseismic barriers. The effect of the barriers on rupture propagation is assessed using results from dynamic models of the earthquake cycle. We show that, accounting for measurement and methodological uncertainties, the MHT is prone to rupturing in M8.7 earthquakes every T>200 yr, with M>9.5 events being greatly improbable. The methodology also allows to estimate the probability of the position of earthquakes on the fault based on the effect of the seismic barriers and their magnitude. This study provides a straightforward and computationally efficient method for estimating regional seismic hazard accounting for the full physics of fault slip.