关键词: 芦山7.0级地震, 地表破裂迹象, 芦山-龙门隐伏推测断裂, 发震构造

Abstract:

The co-seismic surface rupture signs of the "4.20" Lushan M_S7.0 earthquake are found at Longmen Township,Lushan County. The sites of rupture signs have a linear distribution with a 2～3km length and N40°～50°N strike. The maximum shortening of the rupture is about 8cm,uplifting is about 1～2cm. Strike-slip component is not observed,but the dynamic process of the earthquake is characterized by compression from northwest to southeast. The observed co-seismic surface ruptures can be oblique shear-fissure,or thrusting crack,however most of them are extensive fissures,which can be explained by the local extensive stress-field on the top of the thrust bending. Although these ruptures have different geometric shapes or variant mechanic features,they similarly reflect the northwest-southeast compression and the surface lift-bending on the top of a thrusting seismogenic structure. Comparing with Dachuan-Shuangshi Fault(frontal fault)and Dayi-Mingshan Fault(piedmont fault),Lushan-Longmen presumed blind fault is more likely the seismogenic fault,which is also consistent with the results of the Lushan earthquake sequence relocations and the seismic intensity contours. As the seismogenic fault of the Lushan earthquake has surpassed the frontal fault of Longmen Shan,it may be a new-generated tectonics,which implies that it is important to re-evaluate the seismic risk at the piedmont area of the Longmen Shan. However,the conclusions are still very primary and geophysical survey is needed to demonstrate the existence of the Lushan-Longmen presumed blind fault.

Key words: Lushan M_S 7.0 earthquake, surface rupture, Lushan-Longmen presumed blind fault, seismogenic structure