We examine the source parameters of four Mw≥7.0 intraslab earthquakes that occurred near the Tohoku coast over the past two decades: 2003, 2011, 2021, and 2022. By analyzing the finite fault slip histories constrained by inland strong motion observations, we found that these earthquakes occurred within the upper plane of the subducted Pacific Plate due to downdip compression caused by plate unbending. These earthquakes have a more compact fault area and higher stress drop compared to shallow crustal earthquakes. Additionally, intraslab earthquakes have much slower relative rupture velocity than shallow crustal earthquakes. Good spatial correlations between the static stress drop and slip rate are found, which may suggest the compatibility between dynamic stress drop and static stress drop. The rupture area, average slip, asperity area, average static stress drop over the entire fault, and asperities are consistent with the reported scaling relationship for global intraslab earthquakes within a similar depth range. Using plate unbending, we found the recurrence intervals of these intraslab earthquakes are around 600 years, which is comparable with that of the 2011 Tohoku earthquake. A visual spatial-correlation between the locations of these earthquakes and seismicity in the lower plane is reported. These findings provide insights into the tectonic background and source parameters of intraslab earthquakes in the Tohoku region and contribute to better seismic hazard assessment.

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.