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We present 10‐year continuous seismic velocity changes from 2007 to 2017 around the Longmenshan fault zone, where the 2008 Mw 7.9 Wenchuan earthquake and the 2013 Mw 6.6 Lushan earthquake occurred. We collected continuous waveforms recorded by 20 broadband stations covering the entire Longmenshan fault zone and used three‐component ambient noise correlation techniques to measure the velocity changes in four different period bands. Our results show that a significant drop, 0.04–0.06%, occurred in the coseismic velocity at the time of the Wenchuan earthquake, near the rupture zone for the period bands of 1–3 and 3–8 s. In addition, only one fourth of the coseismic velocity drop has been recovered 9 years after the earthquake. We also observed a subtle velocity drop, 0.0066%, delayed by ~100 days relative to the time of the mainshock in the period bands of 6–15 s. In the source region of the Lushan earthquake, we detected a weak but reliable coseismic velocity change of ~0.01% in the period band of 1–3 s. The physical mechanism of the seismic velocity change could involve the damage in the shallow subsurface layer (<3 km), the damage in the fault zone at depth (~10 km), and the postseismic slip along the deep rupture zone up to ~20 km. The uncommonly slow postseismic velocity recovery indicates the slow healing of the Longmenshan fault zone after the Wenchuan earthquake, which may be associated with the low rate of stress loading onto the fault zone. Key Points: The 2008 Wenchuan earthquake caused velocity changes in the fault zone at depth (~20 km)An uncommonly slow postseismic velocity recovery was observed, probably implying a slow healing of the Longmenshan fault zoneA weak but reliable coseismic velocity change of ~0.01% was detected related to the 2013 Lushan earthquake [ABSTRACT FROM AUTHOR]

A detailed three-dimensional (3-D) P-wave velocity model of the crust and uppermost mantle under the Chinese capital (Beijing) region is determined with a spatial resolution of 25 km in the horizontal direction and 4–17 km in depth. We used 48,750 precise P-wave arrival times from 2973 events of local crustal earthquakes, controlled seismic explosions and quarry blasts. These events were recorded by a new digital seismic network consisting of 101 seismic stations equipped with high-sensitivity seismometers. The data are analyzed by using a 3-D seismic tomography method. Our tomographic model provides new insights into the geological structure and tectonics of the region, such as the lithological variations and large fault zones across the major geological terranes like the North China Basin, the Taihangshan and the Yanshan mountainous areas. The velocity images of the upper crust reflect well the surface geological and topographic features. In the North China Basin, the depression and uplift areas are imaged as slow and fast velocities, respectively. The Taihangshan and Yanshan mountainous regions are generally imaged as broad high-velocity zones, while the Quaternary intermountain basins show up as small low-velocity anomalies. Velocity changes are visible across some of the large fault zones. Large crustal earthquakes, such as the 1976 Tangshan earthquake (M=7.8) and the 1679 Sanhe earthquake (M=8.0), generally occurred in high-velocity areas in the upper to middle crust. In the lower crust to the uppermost mantle under the source zones of the large earthquakes, however, low-velocity and high-conductivity anomalies exist, which are considered to be associated with fluids. The fluids in the lower crust may cause the weakening of the seismogenic layer in the upper and middle crust and thus contribute to the initiation of the large crustal earthquakes. [Copyright &y& Elsevier]