关于芦山7.0级地震在龙门一带是否存在同震地表破裂的讨论

DISCUSSION ON WHETHER THERE ARE COSEISMIC SURFACE RUPTURES OF THE LUSHAN M_S 7. 0 EARTHQUAKE AT LONGMEN AREA AND ITS IMPLICATIONS

4.20芦山地震后,有学者在芦山县龙门乡发现一系列的线性裂缝和砖块的旋转变形等"地震地表破裂迹象",由此推测芦山—龙门一线存在隐伏逆断裂,并认为该断裂有可能是此次地震的发震断裂。因此,进一步探讨芦山—龙门一线是否存在潜在的发震断裂,无论是对研究芦山7.0级地震的发震断裂,还是对灾区的重建指导都十分重要。在龙门乡开展了地质灾害调查、跨谷地的地质剖面实测,槽探和人工地震勘探等工作。结果显示:至少在800m深度范围内,不存在芦山-龙门隐伏断裂。此带上的地裂缝等现象不是由断层位错引起,而更可能是地震动在阶地陡坎附近造成的地基或边坡效应所致。

An Ms 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 meizos- eismal area of the Lushan event is IX （the Chinese Seismic Intensity Scale）. The meizoseismal area strikes NE, and is approximately 24km long and 1 lkm wide. In the post-earthquake emergency scien- tific 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. Mean- while, artificial seismic prospecting outcome, which shows nonexistence of the Lushan-Longmen pre- sumed 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.