1. College of Geo-Exploration Science and Technology, Jilin University, Changchun 130026, China;
2. Laboratory of Seismology and Physics of Earth's Interior, University of Science and Technology of China, Hefei 230026, China

New Vp and Vs models of the aftershock gap between the 2013 Lushan and 2008 Wenchuan earthquakes were obtained using 7190 events recorded by 102 stations in the southeastern margin of the Tibetan Plateau. The new velocity models and event locations were inverted by the regional-scale version of double-difference tomography algorithm. The new velocity structure shows that the aftershock gap is an obviously low-velocity zone in the upper crust, whereas the aftershock regions of the Lushan and Wenchuan earthquakes show high-velocity anomalies. The low-velocity anomaly of the aftershock gap in the upper crust may indicate that the materials of the gap are weak and ductile, which is not prone to accumulate stress and cause big earthquakes. As a result, it is less likely that the big earthquakes will occur in the gap in the future.