The mainshock of April 20, 2013 Sichuan Lushan M _S7.0 earthquake was relocated using a 3-D velocity model. Double difference algorithm was applied to relocate aftershock sequences of Lushan earthquake. The locations of 2405 aftershocks were determined. The location errors in E-W, N-S and U-D direction were 0.30, 0.29 and 0.59 km on average, respectively. The location of the mainshock is 102.983°E, 30.291°N and the focal depth is 17.6 km. The relocation results show that the aftershocks spread approximately 35 km in length and 16 km in width. The dominant distribution of the focal depth ranges from 10 to 20 km. A few earthquakes occurred in the shallow crust. Focal depth profiles show fault planes dip to the northwest, manifested itself as a listric thrust fault. The dip angle is steep in the shallow crust and gentle in the deep crust. Although the epicenters of aftershocks distributed mainly along both sides of the Shuangshi-Dachuan fault, the seismogenic fault may be a blind thrust fault on the eastern side of the Shuangshi-Dachuan fault. Earthquake relocation results reveal that there is a southeastward tilt aftershock belt intersecting with the seismogenic fault with y-shape. We speculate it is a back thrust fault that often appears in a thrust fault system. Lushan earthquake triggered the seismic activity of the back thrust fault.

The Shanxi rift is located in the central part of the North China Craton (NCC). With strong tectonic deformation and intense seismic activity, its crust‐mantle deformation and deep structure have always attracted wide attention. Using teleseismic events observed in a dense network of 610 temporary and 127 permanent stations in the central NCC, we obtained the crust‐mantle S wave velocity structures by the joint inversion method of receiver functions and surface wave dispersion data. Our results show that the crust thickens in the northern part of the Shanxi rift (41 km) and thins in the southern part (35 km). The Taiyuan and Linfen basins, located in the central part, have high‐velocity zones in the lower crust and upper mantle; beneath the Yuncheng basin in the south, there are low‐velocity zones in the lower crust and uppermost mantle (30–80 km); the Datong basin, located in the northern part of the rift, exhibits a wide range of low‐velocity anomalies in the middle to lower crust and upper mantle. We speculate that the destruction of the NCC and associated lithospheric thinning had a significant impact on the southern part of the rift, but is still in its early stage in the central part, which retains most of the craton features. An upwelling of the asthenospheric magma occurred beneath the western part of the Datong basin. The horizontal deflection of the asthenospheric flow causes low‐velocity anomalies in its surrounding area, which is consistent with LAB topography.

In summers of 2002 and 2003, temporary seismic stations had recorded a large number of small earthquakes and a series of swarms near Changbaishan Tianchi volcano. Earthquake location result shows that these earthquakes mainly occurred near the Tianchi caldera. Almost all swarms were concentrated at southwest of the caldera, and no swarms occurred in northeast area where earthquakes densely concentrated. In other seasons, the permanent station CBS is the only seismic station to monitor volcanic earthquakes in Tianchi volcano. Waveform correlation analysis of seismic data recorded at CBS in different time shows that earthquake swarms occurred in other seasons also concentrated in the southwest Tianchi Lake. High‐precision relative location shows that hypocenters of earthquake swarm distributed along northwest with a dip angle of 80° to southwest. During the July 13, 2003 earthquake swarm the hypocenters migrated from deep to shallow and deeper events had upward first motion directions almost at all stations. That means they had obvious expansion component in source mechanism. Taking into account of significant surface deformation in Changbaishan Tianchi volcano since 2002, geochemical anomalies and harmonic‐spectral earthquakes, we believe that the earthquake swarm activity was caused by magmatic and hydrothermal activity and pressure increase of magma near the depth of 5km.

The cratonic Sichuan Basin is located east of the Tibetan Plateau, and is surrounded by mountains that have undergone complex deformation and uplift since the Cenozoic. Imaging mantle structure is important for understanding its formation, and to date most models suggest a deep cratonic root underlies the basin, blocking eastward extrusion of lithospheric material beneath Tibet. Here, we obtain detailed upper mantle structure from teleseismic tomography in the region utilizing travel time data from earthquakes recorded at 506 seismic stations, including 25 new stations in the poorly sampled Sichuan Basin. Contrasting to previous models, we show eastward and southeastward dipping high‐velocity anomalies extending eastward ∼150–400 km into the upper mantle from the Sichuan Basin. We suggest, the southeastward subduction of the Yangtze Block occurred in the Mesozoic and may be reactivated in the Cenozoic, with the relatively thin and weak lithosphere to the east of the Sichuan Basin prone to deformation in response to the eastward growth of the Tibetan Plateau. A west‐dipping high‐velocity anomaly beneath eastern Tibet is interpreted as delaminated lithosphere. This delamination may accelerate the development of the Xianshuihe fault zone and the horizontal extrusion of the Tibetan Plateau. Beneath the East Qinling orogen, the eastward extrusion of the plateau material is not obvious suggesting limited horizontal lithospheric extrusion is present north of the Sichuan Basin.