Abstract

We applied a backprojection (BP) analysis based on a 3D global P‐wave tomography model to image the spatiotemporal rupture process of the 2015 Mw 7.8 Nepal earthquake. First, we used BP to determine the centroid locations of five aftershocks with 1D and 3D models, and the results show that the 3D model BP possesses a higher spatial resolution than the 1D model. Then, we used data from three different arrays at varying azimuths in North America, Australia, and Europe and compared the results of the 1D and 3D models. The comparison indicates that, from aspects of rupture direction, pattern, and speed, we obtain a more mutually concordant result using a 3D model with data from different azimuths. To further understand the significance of using a 3D model instead of a 1D model, we compared the travel‐time difference of the two models for three arrays and found the reason why the improvement of the Australian network is the most obvious for this earthquake. Our 3D model BP result reveals a unilateral and southeastward high‐frequency rupture front for which the geometry is a curved line protruding in the subduction direction (from the Indian plate toward the Eurasian plate) slightly, which precisely coincides with the northern edge of the large slip area obtained by the finite‐source inversion and dominates the down‐dip area. The rupture speed is quantified at 2.42.5  km/s, and the rupture length is 120  km. Compared to the existing calibrated BP method with aftershock information, the 3D model BP method could image the rupture process of earthquakes in quick response.

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