Standard Back-Projections (BPs) use P phase recordings at large aperture arrays within teleseismic distances (30°-90°) to image earthquake sources. However, the majority of sizable arrays are in the northern hemisphere, leaving many southern hemisphere earthquakes beyond the teleseismic range. We extend the BP method by utilizing seismic waves traveling through the Earth’s core, expanding our capability to image earthquakes worldwide. Our core phase BPs incorporate PKIKP (150°-180°) and PKP (145°-175°) phases. We evaluate their theoretical resolutions using 1-D and 2-D array response functions and test uncertainties by adding white noise to coherent waveforms. Tests show that core phase BPs achieve resolutions and uncertainties comparable to P phase BP. We validate the method using a synthetic model of a unilateral rupture (Mw 7.45, 2 km/s) and demonstrate accurate recovery of rupture direction, length, and speed. Applying core phase BPs to the 2010 Mw 8.8 Chile and 2015 Mw 7.1 southeast Indian Ridge earthquakes, we compare our results with published BPs and/or slip models, confirming the feasibility and reliability of core phase BPs. We then apply core phase BPs to five understudied earthquakes in the southwest Pacific region, providing insights into these pelagic earthquakes. Core phase BPs play a crucial role in scenarios where teleseismic arrays are unavailable, and have weaker array-dependent effect and better performance in bilateral rupture imaging. Finally, we discuss the limitations of core phase BPs and outline potential avenues for future research.

We image the rupture process of the 2021 Mw 7.4 Maduo, Tibet earthquake using slowness-enhanced back-projection and joint finite fault inversion, which combines teleseismic broadband body waves, long-period (166-333 s) seismic waves, and 3D ground displacements from radar satellites. The results reveal a left-lateral strike-slip rupture, propagating bilaterally on a 160-km-long north-dipping sub-vertical fault system that bifurcates near its east end. About 80% of the total seismic moment occurs on the asperities shallower than 10 km, with a peak slip of 5.7 m. To simultaneously match the observed long-period seismic waves and static displacements, notable deep slip is required, despite a tradeoff with the rigidity of the shallow crust. This coseismic deep slip within the ductile middle crust could result from strain localization and dynamic weakening. Local crustal structure and synthetic long-period Earth response for Tibet earthquakes thus deserve further investigation. The WNW branch ruptures ~75 km at ~2.7 km/s, while the ESE branch ruptures ~85 km at ~3 km/s, though super-shear rupture propagation possibly occurs during the ESE propagation from 12 s to 20 s. Synthetic back-projection tests confirm overall sub-shear rupture speeds and reveal a previously undocumented limitation caused by the signal interference between two bilateral branches. The stress analysis on the forks of the fault demonstrates that the pre-compression inclination, rupture speed, and branching angle could explain the branching behavior on the eastern fork.