Coseismic, Postseismic and Interseismic Coulomb Stress Evolution Along the Himalayan Main Frontal Thrust Since 1803

摘要

The Himalayan Main Frontal Thrust is the most active fault in the Himalayan subduction zone, with a high degree of locking and a large thrust rate. Gaps on the Himalayan Main Frontal Thrust have been free of strong earthquakes for hundreds of years and the surrounding areas are densely populated, so it is significant to study the evolution law and the current status of stress along the Himalayan Main Frontal Thrust. Based on a lithospheric viscoelastic layered medium model, we analyzed the interseismic stress accumulation along the Himalayan Main Frontal Thrust and the coseismic and postseismic stress disturbance on the fault surface caused by nine Mw >= 7.5 earthquakes since 1803. The results showed that the stress disturbance along the Himalayan Main Frontal Thrust caused by historical earthquakes have promoted most of the subsequent earthquakes, but the coseismic and postseismic stress changes caused by the historical earthquakes on the faulty surface of subsequent earthquakes are not significant, because of the long distance between strong earthquakes. Interseismic stress enhanced the stress level of the majority of fault planes in the study area and played a dominant role in the stress evolution and strong earthquake preparation along the Himalayan Main Frontal Thrust. The recurrence interval of Mw 7.5-7.9 earthquakes on the Himalayan Main Frontal Thrust is 70-250 years and the recurrence interval of Mw > 8 earthquakes which rupture the whole seismogenic layer may be longer than 500 years. This agrees with historical seismic records. The elapsed time of strong earthquakes in the four seismic gaps is between 460 and 915 years and the possibilities of Mw 8 earthquakes in the future 10 years always exist, including a probability of higher than 50% in three seismic gaps. The peak of cumulative Coulomb stress in the seismic gaps is more than 1 MPa, and the seismic hazard on the Himalayan Main Frontal Thrust needs further attention.