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[1] Pn travel times are useful for studying crustal and uppermost mantle structure and regional tectonics because they are affected by crustal velocity and thickness as well as uppermost mantle velocity and anisotropy. We obtained 57,740 Pn travel time picks from 5433 earthquakes and 307 stations from Chinese national and provincial earthquake bulletins and the International Seismological Center bulletins to invert for Pn velocity variation and anisotropy and station delays in China. Our inversion reveals significant features that correlate with surface geology. The main results are as follows: (1) The Pn velocities show a mosaic of very fast and very slow anomalies, mirroring the heterogeneous geology of China at the surface. The Pn velocities are high beneath the major basins in the west (Sichuan, Qaidam, west Tarim, Tulufan, and Junggar) and low in areas of active volcanoes (Myanmar and western Yunnan) and Quaternary volcanism in northern Tibet, in seismically active areas in north China and Tien Shan, and in the southern part of south China (the Hainan plume). (2) The Pn anisotropy beneath the major basins in the west is generally weak. Strong anisotropy is found beneath high-deformation regions (the Tibetan Plateau, southeastern margin of the Tibetan Plateau, western Tien Shan, and part of north China), suggesting the anisotropy is likely related to recent largescale tectonic activity. (3) A large area of north China shows prominent low Pn velocity beneath Archean basement with thin crust. Our observations are consistent with rifting, lithospheric thinning, and mantle upwelling in the region. The Pn anisotropy is consistent with a dextral simple shear in the NNE direction in the lithosphere mantle during the last (and ongoing) major deformation period. (4) The Pn velocity in northern Tibet is generally lower than that in the south. Southern Tibet has significant E-W structure. Lowvelocity anomalies can be traced from northern Tibet across southwestern Tibet and south central Tibet to near the India plate. Anisotropy is absent beneath much of the Himalaya block, but consistent anisotropy with E-W fast direction is present beneath the Lhasa block and large anisotropy (up to 4%) is observed in low-velocity regions of the northern and western Tibet. Complex station delays in the eastern margin of the plateau suggest that the whole crust may be highly deformed. The anisotropy pattern in the southeastern margin of the Tibetan Plateau suggests a mantle lithospheric deformation similar to the clockwise rotation of material observed at the surface. (5) Crustal thicknesses inferred from our station delays are consistent with previous models, which correlate well with surface topography.

We analyzed 18 high-quality waveform doublets with time separations of up to 35 years in the South Sandwich Islands region, for which the seismic signals have traversed the inner core as PKP(DF). The doublets show a consistent temporal change of travel times at up to 58 stations in and near Alaska, and they show a dissimilarity of PKP(DF) coda. Using waveform doublets avoids artifacts of earthquake mislocations and contamination from small-scale heterogeneities. Our results confirm that Earth's inner core is rotating faster than the mantle and crust at about 0.3 degrees to 0.5 degrees per year.

In an effort to confirm inner core anisotropy, we conducted a systematic search for PKP ray paths with various angles from the Earth's spin axis. In particular, we studied paths nearly parallel to the spin axis (polar paths) and those nearly parallel to the equatorial plane (equatorial paths). Data for earthquakes and explosions were collected from Worldwide Standardized Seismograph Network (WWSSN), Long Range Seismic Measurements (LRSM), and Global Digital Seismograph Network (GDSN). Absolute times (DF, BC) and differential times (BC‐DF, AB‐DF) as well as waveform data were examined. For all polar paths, differential times of BC‐DF consistently yield residuals of 1.5 to 3.5s larger than equatorial paths. Absolute DF time residuals exhibit anomalies of the same magnitude (1 to 4s) with DF being early along polar paths while BC residuals have no obvious correlation with the differential time anomalies. DF phases appear multi‐pathed for polar paths and are relatively simple for equatorial paths. These results coupled with previous studies suggest an axisymmetric anisotropy at the top of the inner core.

What happened to the Indian mantle lithosphere (IML) during the Indian-Eurasian collision and what role it has played on the plateau growth are fundamental questions that remain unanswered. Here, we show clear images of the IML from high-resolution P and S tomography, which suggest that the subducted IML is torn into at least four pieces with different angles and northern limits, shallower and extending further in the west and east sides while steeper in the middle. Intermediate-depth earthquakes in the lower crust and mantle are located almost exclusively in the high-velocity (and presumably strong) part of the Indian lithosphere. The tearing of the IML provides a unified mechanism for Late Miocene and Quaternary rifting, current crustal deformation, and intermediate-depth earthquakes in the southern and central Tibetan Plateau and suggests that the deformations of the crust and the mantle lithosphere are strongly coupled.