Spatial relation between source properties and aftershock distribution of the 2015 Mw7.9 Nepal earthquake

Using the aftershock catalog from the 2015 M(w)7. 9 Nepal earthquake, we examined where the aftershocks occurred relative to the spatial distribution of the stress change based on kinematic source inversion of the fault slip distribution along the main fault. The patterns of the source slip and stress change distributions were much more concentrated and isolated on the main fault plane. About 70% of aftershocks with M>3. 0 occurred in the stress increasing area, while a few aftershocks occurred in the area where stress dropped but with high stress change gradient. To obtain a source slip model to explain the aftershock triggering mechanism, we calculated the source spectrums of slip and stress change in the wave-number domain. The resultant spectrum patterns of slip and stress change on the main fault exhibited decay rates of approximately k(-3) and k(-2), respectively. We calculate the equilibrium radius r(e) which indicates where the stress drop changes its sign, is approximately 0. 7a and the area with a positive stress drop is approximately 51% of the total area of the asperity patch. This result indicates that a circular quadratic stress drop model is appropriate for characterizing the rupture process of the Nepal earthquake. This model shows that a positive stress change can occur in regions where a slip displacement exists, which implies that the aftershock might occur in the main fault slip zone, partially explaining the spatially distributed aftershock pattern. Furthermore, the circular quadratic stress drop model more accurately represented the source rupture behavior of the 2015 Nepal earthquake than the circular constant stress drop model.