关键词: 芦山7.0级地震, 龙门乡, 地裂缝, 发震构造

Abstract: An M_S 7.0 earthquake attacked southern segment of the Longmenshan Fault zone on 20 April 2013, in Lushan County, Sichuan Province, southwest of China. The seismic intensity of the meizoseismal area of the Lushan event is Ⅰ Ⅹ(the Chinese Seismic Intensity Scale). The meizoseismal area strikes NE, and is approximately 24km long and 11km wide. In the post-earthquake emergency scientific survey, some members found a series of co-seismic surface rupture signs at Longmen Township, one of the most damaged areas by this quake, north of Lushan County. The reported typical surface rupture signs include intensive shear-fissures along the channel at Zhanghuo Group, rotation of bricks near a white tower at Wanghuo Group, and lots of extensive cracks. On the basis of analyzing such surface rupture signs, Han et al., (2013)deduced that there might be a blind fault along Lushan County and Longmen Township(named the Lushan-Longmen presumed blind fault), and this fault probably was the seismogenic fault. Therefore, to confirm whether there is a potential seismogenic fault along Lushan and Longmen is very important not only to research of seismogenic fault for this earthquake but also to the reconstruction in the disaster-hit areas. Through surface ruptures surveying and trench excavating, we conclude that: there are no co-seismic surface ruptures at Longmen. Meanwhile, artificial seismic prospecting outcome, which shows nonexistence of the Lushan-Longmen presumed blind fault at least 800m below the ground surface, also supports our idea. Consequently, the reported shear-fissures and extensive cracks are not produced by the seismogenic fault, but most likely by ground shaking during the earthquake.

Key words: the Lushan M_S 7.0 earthquake, Longmen Township, ground fissures, seismogenic structure