We use receiver functions calculated for data collected by the INDEPTH‐IV seismic array to image the three‐dimensional geometry of the crustal and upper mantle velocity discontinuities beneath northeastern Tibet. Our results indicate an average crustal thickness of 65 to 70 km in northern Tibet. In addition, we observe a 20 km Moho offset beneath the northern margin of the Kunlun Mountains, a 10 km Moho offset across the Jinsha River Suture and gently northward dipping Moho beneath the Qaidam Basin. A region in the central Qiangtang Terrane with higher than normal crustal Vp/Vs ratio of ∼1.83 can be the result of the Eocene magmatic event. In the Qiangtang Terrane, we observe a significant lithospheric mantle discontinuity beneath the Bangong‐Nujiang Suture at 80 km depth which dips ∼10° to the north, reaching ∼120 km depth. We interpret this feature as either a piece of Lhasa Terrane or remnant oceanic slab underthrust below northern Tibet. We detect a ∼20 km depression of the 660‐km discontinuity in the mantle transition zone beneath the northern Lhasa Terrane in central Tibet, which suggests this phase transition has been influenced by a dense and/or cold oceanic slab. A modest ∼10 km depression of the 410‐km discontinuity located beneath the northern Qiangtang Terrane may be the result of localized warm upwelling associated with small‐scale convection induced by the penetration of the sinking Indian continental lithosphere into the transition zone beneath the central Tibetan Plateau.

Significance The Songpan-Ganzi terrane lies in the central-east of the Tibetan Plateau, which was considered a stable block in some tectonic models. Its deformation mode is of crucial importance for understanding the evolutionary history and seismic hazard of the plateau. The recent Maduo earthquake occurred inside the terrane. We resolve a bilateral rupture process with distinct super- and subshear rupture modes for this event. We also find that pervasive folding structures that are aligned by shear deformation in the current Songpan-Ganzi terrane are responsible for the seismic wave anisotropy and shear strain orientation in its upper crust. Its deformation mode can be classified as distributed simple shear, which receives shear loads from side walls and produces internal earthquakes.

The 13 November 2016 Mw 7.8 Kaikoura, New Zealand, earthquake was investigated using teleseismic P waves. Backprojection of high‐frequency P waves from two regional arrays shows unilateral rupture of at least two southwest‐northeast striking faults with an average rupture speed of 1.4–1.6 km/s and total duration of ~100 s. Guided by these backprojection results, 33 globally distributed low‐frequency P waves were inverted for a finite fault model (FFM) of slip. The FFM showed evidence of several subevents; however, it lacked significant moment release near the epicenter, where a large burst of high‐frequency energy was observed. A local strong‐motion network recorded strong shaking near the epicenter; hence, for this earthquake the distribution of backprojection energy is superior to the FFM as a guide of strong shaking. For future large earthquakes that occur in regions without strong‐motion networks, initial shaking estimates could benefit from backprojection constraints.

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A finite-difference modeling plus slowness analysis method is developed to investigate near-source explosion energy partitioning and Lg-wave excitation. The finite-difference method is used to calculate seismic wave excitation and propagation, and an embedded array slowness analysis is used for quantifying how energy will be partitioned into the long-range propagation regime. Because of its high efficiency, the method can simulate near-source processes using very fine structures. A large number of source and model parameters can be examined for broadfrequency ranges. As examples, P-pS-to-Lg and S*-to-Lg conversions in the presence of near-source scattering are tested as mechanisms for Lg-wave excitation. The numerical results reveal that the depth of the source and the depth of the scattering process have strong effects on P-to-S conversion and partitioning of energy into trapped or leaking signals. The Lg-wave excitation spectra from these mechanisms are also investigated. The modeling shows that S*-to-Lg excitation is generally stronger for low frequencies and shallow source depths whereas P-pS-to-Lg scattering is stronger for high frequencies.

High-quality vertical component seismograms of teleseismic P waves recorded at 151 stations of the European seismic network have been used to image the rupture process of the 2011 Tohoku Earthquake rapidly by a two-step back-projection method. The spatio-temporal distribution of rupture fronts suggests that the earthquake ruptured northeastwards and southwestwards over a total length of more than 340 km during at least 143 s. The fact that three fault segments ruptured at regions having different lateral heterogeneities implies that the earthquake comprised three sub-events. The first sub-event ruptured northeastwards during the first 25 s, and then turned to the northwest direction. The second sub-event ruptured at a relatively high speed of 2.78∼4.70 km/s. The third sub-event ruptured with a direction variation from southwest to southeast near the latitude of 37• . In addition, considering that the first front of the second sub-event appeared at 74.6 s and was about 28 km away from the epicenter, we propose that the second sub-event might have been triggered by the localized increase in tectonic stress in the vicinity of the hypocenter that resulted from the rupture of the first sub-event.

A rapid, robust multiarray backprojection method was applied to image the rupture pattern of the 2015 Gorkha, Nepal Mw7.8 main shock and its Mw7.3 aftershock. Backprojected teleseismic P wave trains from three regional seismic arrays in Europe, Australia, and Alaska show that both earthquakes ruptured unilaterally and primarily eastward, with rupture speeds potentially decreasing with depth. The rupture of the main shock first extended ESEward at ∼3.5 km/s over ∼120 km, with later rupture propagation further downdip on the eastern segment at ∼2.1 km/s. The aftershock ruptured the fault SE of the main shock's ruptured plane. It began to rupture updipward for ∼20 km at a speed around 1.2 km/s, then it may have accelerated to 3.5 km/s for the next 50 km. The apparent depth‐dependent rupture speeds of the two earthquakes may be caused by along‐dip heterogeneities in fault strength, with a higher stress concentration on the updip part of the Nepalese Main Himalayan Thrust.

a Mw 8.6 strike-slip earthquake struck the northern Sumatra offshore region, and became the largest intraplate event ever recorded there. Preliminary study results show a remarkably complex rupture pattern, on a fault system manifested by north-south trending paleotransform faults and east-west striking abyssal hill fabric. To image the rupture pattern of the earthquake, we backprojected teleseismic P wave recordings observed at three regional seismic networks (EU, AU, and F-net). Our results indicate that the earthquake ruptured on a conjugate fault system, composed of two subparallel WNW-ESE trending faults, and a NNE-SSW striking fault in between, for a duration of at least 120 s. The rupture started at the WNW end of the first WNW-ESE trending fault located at the east of the conjugate fault system, and propagated toward ESE. It then jumped to the second NNE-SSW trending fault located west of the first fault, and first extended SSWward and 15 s later NNEward. After its end on the second fault, the rupture jumped onto the third WNW-ESE trending fault and continued WNWward. The static Coulomb stress changes calculated from the rupture of the first and then the second faults, based on simplified uniform slip models, suggest that initiation of the rupture on the second fault could be statically and dynamically triggered by the first fault. However, the third fault was primarily dynamically triggered by S or even Love waves radiated from the southern branch of the second fault.