Coulomb Stress Modeling and Seismicity in the Western Himalaya, India Since 1905: Implications for the Incomplete Ruptures of the Main Himalayan Thrust

The along-strike terminations of seismic ruptures on the Main Himalayan Thrust (MHT), western Himalayan segment, due to four earthquakes of magnitude (Mw) >= 6.6 in 1905-2019 are investigated using the Coulomb failure criterion. For the 1975 Kinnaur earthquake (Mw 6.8), stress perturbations are controlled by the secondary fault structures, which generated stress heterogeneities within the study area and have limited the mainshock rupture propagation in the NW-SE direction along strike, impeding the rupture to reach the Himalayan front. The ramp geometry of the MHT played a significant role during the 1991 Uttarkashi and 1999 Chamoli earthquakes, inhibiting the seismic ruptures from accelerating toward the surface. Besides, the geometry marks the presence of complex Lesser Himalayan duplexes, which accumulates the resultant coseismic stress from the two earthquakes. The Coulomb stress modeling of the studied earthquakes suggests a lateral increase in stress interactions along the strike for the 1905 Kangra, the 1991 Uttarkashi, and the 1999 Chamoli events and across the strike for the 1975 Kinnaur earthquake in the western Himalaya. Finally, we infer that the tectonic loading of the MHT dominates the present-day stress perturbations in the western Himalaya.

Automated summary

The study reveals that secondary fault structures control stress perturbations during earthquakes, while the geometry of faults limits rupture propagation and complex duplexes accumulate coseismic stress.