SURFACE RUPTURE AND HAZARD CHARACTERISTICS OF WENCHUAN EARTHQUAKE WITH MAGNITUDE 8.0 IN SICHUAN PROVINCE

On May 12 of 2008t,he Wenchuan M8.0 earthquake in Sichuan Province occurred on the Longmenshan tectonic belt at the eastern margin of the Qinghai—Tibet Plateau.Through field investigation and survey,the major surface rupture occurred on the segment of Beichuan—Yinxiu fault from the southwest of Yingxiu to Shikanzi of Nanba in Pingwu County,with a length of 220 km.It shows the fault produces a thrust and dextral slip.The maximum displacement along the fault is about 6 m;horizontal component is equivalent to the vertical direction.Another segment from Xiange in Dujiangyan City to Sangzao in Anxian County produces a 100 km coseismic surface rupture in length,also displaying a thrust and dextral characteristic of the fault.The maximum vertical displacement on this segment is about 2 m;and the ratio of the vertical component and the horizontal is between 1∶3 and 1∶1.The distribution of surface rupture and the characteristics of coseismic displacements show that the thrust-dextral slip of Beichuan—Yingxiu fault led to the Wenchuan M8.0 earthquake,representing strong ground motion destroy,surface cracking directly and secondary geological hazards(such as landslip,hillside creep) pulling down or burying the civic structures.Based on macroscopical surveys,tudies of InSARa,nd records of seismographs,the axis of isoseismal line extends at N40°–50°E orientation along the Longmenshan tectonic belt.Its typical characteristic is a unilateral,multipoint instantaneous rupture.The earthquake produced three intensity damaged areas with seismic magnitude XI,and remarkably enhanced the damages of normal earthquake attenuation in the North Sichuan province,the South Gansu Province and Hanzhong region of Shaanxi Province.