Supershear rupture, in which a fracture's crack tip expansion velocity exceeds the elastic shear wave velocity, has been extensively investigated theoretically and experimentally and previously inferred from seismic wave observations for six continental strike‐slip earthquakes. We find extensive evidence of supershear rupture expansion of an oceanic interplate earthquake, the 5 January 2013M_w = 7.5 Craig, Alaska earthquake. This asymmetric bilateral strike‐slip rupture occurred on the Queen Charlotte Fault, offshore of southeastern Alaska. Observations of first‐arrivingSnandSgshear waves originating from positions on the fault closer than the hypocenter for several regional seismic stations, with path calibrations provided by an empirical Green's function approach, indicate a supershear rupture process. Several waveform inversion and modeling techniques were further applied to determine the rupture velocity and space‐time distribution of slip using regional seismic and geodetic observations. Both theoretical and empirical Green's functions were used in the analyses, with all results being consistent with a rupture velocity of 5.5 to 6 km/s, exceeding the crustal and upper mantleSwave velocity and approaching the crustalPwave velocity. Supershear rupture occurred along ~100 km of the northern portion of the rupture zone but not along the shorter southern rupture extension. The direction in which supershear rupture developed may be related to the strong material contrast across the continental‐oceanic plate boundary, as predicted theoretically and experimentally. The shear and surface wave Mach waves involve strongly enhanced ground motions at azimuths oblique to the rupture direction, emphasizing the enhanced hazard posed by supershear rupture of large strike‐slip earthquakes.

Quantifying the regional kinematics is critical for understanding the deformation mechanisms of the Tibetan Plateau. In this study, we construct an elastic block model using a dense GPS velocity field to derive the fault slip rates in SE Tibet. We uncover good agreement between GPS and late Quaternary slip estimates, suggesting that the GPS slip rates estimated from our model can represent the long‐term fault motions in SE Tibet. Specifically, our model shows that the slip along the Xianshuihe fault increases from west to east, which may result from the initiation of the Longriba fault. The Litang, Zhongdian, and Xiaojiang faults and the faults bounding the Lijiang block exhibit extensional motions, in agreement with the regional tectonics and earthquake focal mechanisms. In the regions north of the Red River fault whose kinematics can be described through the rotations of subblocks with small residuals, the fault motions agree with focal mechanism patterns and tectonic block models. In regions south of the Red River fault, the right‐lateral shearing among the Red River, Lancang and Sagaing faults appears to explain the first‐order deformation features. However, the relatively large residuals and complex tectonic setting suggest that various other factors, such as asthenospheric flow and the subduction of the Burma plate may also influence the deformation. Thus, a single model extended to interpret all the geodynamic features in SE Tibet, especially south of the Red River fault, may be overly simple, and the extent to which each factor contributes to this deformation requires further study.

Seasonal variations are observed in GPS time series, but are not included in the International Terrestrial Reference Frame (ITRF) models. Unmodeled seasonal variations at sites used for reference frame alignment are aliased into the reference frame parameters and bias all coordinates in the transformed solution. We augment ITRF2008 with seasonal loading models based either on Gravity Recovery and Climate Experiment (GRACE) measurements or a suite of models for atmospheric pressure, continental hydrology, and nontidal ocean loading. We model the seasonal components using either annual and semiannual terms or a nonparametric approach. When we include a seasonal variation model, the weighted root-mean-square misfit after seven-parameter transformation decreases for 70–90% of the daily GPS solutions depending on the network and seasonal model used, relative to a baseline case using ITRF2008. When seasonal variations are included in the reference frame solution, the observed seasonal variations are more consistent with the GRACE-based model at 80–85% of the GPS sites that were not used in the frame alignment. The suite of forward models performs nearly as well as the GRACE-based model for North America, but substantially worse for other parts of the world. We interpret these findings to mean that the use of ITRF2008 without seasonal terms causes the amplitude of seasonal variations in the coordinate time series to be damped down relative to the true loading deformation and that the observed GPS time series are more consistent with a TRF model that includes seasonal variations. At present, a seasonal model derived from GRACE captures seasonal variations more faithfully than one based on hydrologic models.

The Pishan, Xinjiang, earthquake on 3 July 2015 is the one of largest events (M_w 6–7) that has occurred along the western Kunlun Shan, northwestern edge of the Tibetan Plateau in recent time. It involved blind thrusting at a shallow depth beneath the range front, providing a rare chance to gain insights into the interaction between the Tarim Basin and the Tibetan Plateau. Here we present coseismic ground displacements acquired by high‐resolution ALOS‐2 SAR imagery and derived from GPS resurveys on several near‐field geodetic markers after the event. We observed a maximum displacement exceeding 10 cm in the epicentral region. Analysis of the data based on a finite fault model indicates that coseismic slip occurred on a subsurface plane of 22 km × 8 km in size with a dip of about 27° to the north and a strike of 114°, representing partial break of one ramp fault buried in Paleozoic strata at 8–16 km depths beneath the foothill of the western Kunlun Shan. This blind rupture is characterized largely by a compact thrusting patch with a peak slip of 0.63 m, resulting in a stress drop of 2.3 MPa. The source model yields a geodetic moment of 5.05 × 10¹⁸ N · m, corresponding to M_w 6.4. The Pishan earthquake suggests a northward migration of deformation front of the Tibetan Plateau onto the Tarim Basin. Our finding highlights slip along ramp‐décollement faults to build up the western Kunlun Shan as the Tarim slab is subducting beneath western Tibet.