Trapped waves in different sections of Longmenshan fault belt were observed,and the results show the difference between the northern and southern portions of this fault belt.Guanzhuang and Leigu surveying lines are located at the northern portion of the fault belt,and the result indicates that the width of the rupture zone underground in this area is about 160-180 m.The center position of rupture zone underground corresponds to the surface breaking trace,and is equally distributed at the edges of the two fault walls.However,Hongkou surveying line is located at the southern portion of the fault belt,and the result indicates that the width of the rupture zone underground in this area is about 180-200 m.The rupture zone underground is mainly distributed below fault scarp.The Wenchuan Ms8.0 earthquake and Lushan Ms7.0 earthquake both occurred at the Longmenshan fault belt.The results will provide information for the structure background of the two violent earthquakes. Trapped waves in different sections of Longmenshan fault belt were observed, and the results show the difference between the northern and southern portions of this fault belt. Guanzhuang and Leigu surveying lines are located at the northern portion of the fault belt, and the result indicates that the width of the rupture zone underground in this area is about 160-180 m. The center position of rupture zone underground corresponds to the surface breaking trace, and is equally distributed at the edges of the two fault walls.However, Hongkou surveying line is located at the southern portion of the fault belt, and the result indicates that the width of the rupture zone underground in this area is about 180-200 m. The rupture zone underground is mainly distributed below fault scarp. The Wenchuan Ms8.0 earthquake and Lushan Ms7.0 earthquake both occurred at the Longmenshan fault belt. The results will provide information for the structure background of the two violent earthquakes.