At 14:28,May 12,2008,a great earthquake of M_S8.0 occurred in Wenchuan County,Sichuan Province.It produced two ruptures along the Longmenshan Thrust Belt,with the major one of ca.240km along the central fault zone and minor one of ca.70km along the mountain front fault zone,respectively.Baishahe rupture section,located at the southern end of the rupture of Wenchuan earthquake,extends 14km along Baishahe River,11km north of Dujiangyan City.This rupture section presents complicated geometric features,and is composed of several segments.Almost each segment has different strike from others(from 0 to 90°),but the section has an average strike of 50°.Co-seismic slip along the rupture section also shows complexity and multiformity.Up-thrust of the northwest wall is the main vertical co-seismic slip,and the maximum height of fault flexure scarp is 6.5m,but local backward flexure scarps exist there;the right-slip is the main co-seismic strike slip,and the maximum right-slip offset is 4.8m,but local left-slip offset also appears.A rupture plane of 40°/NW∠76° crops out at the northern end of the rupture section.Two groups of striations present on the plane,75°SW and 80°SW.This indicates not only that reverse faulting is major,and strike-slip faulting is minor,but also two rupture events in the earthquake.Based on the analysis of the rupture geometric features and co-seismic slip distribution,we have found the following knowledge: 1)The gradual change of the rupture plane from low angle at source depth to high angle at surface compels the horizontal shortening to transform into uplifting,causing directly the ratio of strike-slip to horizontal shortening approaching to 1,and forming backward fault flexure scarp behind the main rupture zone;2)The direction and amount of strike slip are determined by three factors of strike of rupture,azimuth of reference and gravity;3)The thickness of the overlying unconsolidated deposits affects the scope and style of rupture at the surface.

Field investigations show that the M_S8.0 Wenchuan earthquake of 12^th May 2008 ruptured two NW-dipping imbricate reverse faults along the Longmenshan Fault zone at the eastern margin of the Tibetan Plateau.This earthquake generated a 240km long surface rupture along the Beichuan-Yingxiu Fault characterized by right-lateral oblique faulting and a 90km long surface rupture along the Guanxian-Jiangyou Fault characterized by dip-slip reverse faulting.Maximum vertical and horizontal dispacements of 6.2m and 4.9m,respectively,were observed along the Beichuan-Yingxiu Fault,whereas a maximum vertical displacement of 3.5m occurred along the Guanxian-jiangyou Fault.This co-seismic surface rupture pattern,involving multiple structures,is among the most complicated of recent great earthquakes.Its surface rupture length is the longest among the co-seismic surface rupture zones for reverse faulting events ever reported.Aftershocks recorded by local network clearly outline the hanging wall of the Beichuan-Yingxiu Fault and indicate that the fault dips about 47? to the west.Industry seismic lines,in addition to surface ruptures and aftershocks,allow us to build a 3D model for the rupture geometry that shows crustal shortening is the dominant process along the Longmen Shan to accommodate long-term deformation.Oblique thrusting accomplished by the earthquake indicates that the east-southeastward extrusion of Tibet Plateau accommodates,in part,the continuing penetration of the Indian plate into the Eurasian plate,and this extrusion is transformed at the eastern margin of the Tibetan Plateau into crustal thickening and shortening along the Longmenshan Fault zone that is responsible for the growth of high topography in the region.

On the 12th of May,2008,a devastating M_S 8.0 earthquake struck Wenchuan County,Sichuan Province.The earthquake rupture extends about 200km,and the maximum co-seismic strike-slip displacement and vertical displacement are(4.8±0.2)m and(5±0.2)m,respectively.Only one fault plane(N32°E/NW∠76°)has been found on the southern section of the rupture.The high dip of the fault plane and high angle stria on the fault plane show that the fault is dominated by reverse motion,with a small amount of right-lateral strike-slip component in this segment.

The Yishu Fault zone is a part of the Tanlu Fault zone that passes through Shandong Province and the northern area of Jiangsu. It is composed of 5 nearly parallel faults among which the Anqiu-Juxian Fault is the most important and prominent active fault since late Pleistocene and is usually considered to be the seismogenic fault of the 70 BC M 7 Anqiu earthquake and the 1668 AD M 8¹/₂ Tancheng earthquake. By detailed research in recent years, e.g. the active fault mapping implemented during the “Eighth Five-Year Plan” period, we have gained thorough knowledge of the middle segment of the Anqiu-Juxian Fault to the south of Juxian, while the knowledge of the segment to the north of Juxian has been poor, even no active fault profiles have ever been found. Recent discoveries about the geometry and activity of the Anqiu-Zhuli segment of the Anqiu-Juxian Fault are introduced in this paper. The segment consists of the Nanliu sub-segment, the Shuangguan-Meicun sub-segment and the Zhuli sub-segment. All these sub-segments are distributed along the linear boundary line between hilly area and plain, or locate in the eastern slope of the NNE-trending hills. These fault segments are featured with right-lateral strike-slip movement combined with dip component, and their latest activity age is late Pleistocene to early Holocene. In conclusion, The Anqiu-Juxian Fault is the predominant active structure between Juxian and Changyi in the north of Shandong, and it should have some connections with the occurrence of the 70 BC M 7 Anqiu earthquake. Since the elapsed time is nearly 2100 years, the future earthquake risk in this area shall be emphasized.