Although the kinematics and mechanics of the Yilan-Yitong fault zone (YYFZ) since the Mesozoic-early Cenozoic were studied very well in the past decades,few results about the average recurrence interval of great earthquakes in late Quaternary,which is the most important parameter for us to understand the active tectonics and potential seismic hazard of this crucial structure,were obtained because of its unfavorable work environments.Based on interpretations of high-resolution satellite images and detailed geologic and geomorphic mapping,we discovered that there exist linear fault scarp landforms and troughs in the Shangzhi part of YYFZ with a length of more than 25km.Synthesized results of trenches excavation and differential GPS measurements of terrace surfaces indicate two paleo-events EⅠ and EⅡ occurring in Shangzhi part during the late Holocene,which resulted in ca.(3.2±0.1) m accumulated vertical coseismic displacement with strike-slip motion accompanied by thrusting and shortening deformation.¹⁴C samples dating suggests that event EⅠ might occur at (440±30) and (180±30) a BP and event EⅡ might happen between (4 090±30) and (3 880±30) a BP,and the average recurrence interval of major earthquakes on the YYFZ is around (3 675±235) a.Historical written records discovered from Korea show that the event EⅠ may correspond to the earthquake occurring in AD 1810(Qing Dynasty in Chinese history) in Ningguta area with magnitude 7.0.

The Dengdengshan and Chijiaciwo faults situate in the northeast flank of Kuantanshan uplift at the eastern terminal of Altyn Tagh fault zone, striking northwest as a whole and extending 19 kilometers and 6.5 kilometers for the Dengdengshan and Chijiaciwo Fault, respectively. Based on satellite image interpretation, trenching, faulted geomorphology surveying and samples dating etc., we researched the new active characteristics of the faults. Three-levels of geomorphic surfaces, i.e. the erosion rock platform, terrace I and terrace Ⅱ, could be found in the northeast side of Kuantanshan Mountain. The Dengdengshan Fault dislocated all geomorphic surfaces except terrace I, and the general height of scarp is about 1.5 meters, with the maximum reaching 2.6 meters. Three paleoseismic events are determined since late Pleistocene through trenching, and the total displacement of three events is about 2.7 meters, the average vertical dislocation of each event changed from 0.5 to 1.2 meters. By collecting age samples and dating, the event Ⅰ occurred about 5ka BP, event Ⅱ occurred about 20ka BP, and event Ⅲ occurred about 35ka BP. The recurrence interval is about 15ka BP; and the vertical slip rate since the late Pleistocene is about 0.04mm/a.
The Chijiaciwo Fault, however, dislocated all three geomorphic surfaces, and the general scarp height is about 2.0 meters with the maximum up to 4.0 meters. Three paleoseismic events are determined since late Pleistocene through trenching, and the total displacement of three events is about 3.25 meters, the average vertical dislocation of each event changed from 0.75 to 1.5 meters, and the vertical slip rate since the late Pleistocene is about 0.06mm/a. Although the age constraint of paleoearthquakes on Chijiaciwo Fault is not as good as that of Dengdengshan Fault, the latest event on Chijiaciwo Fault is later than Dengdengshan Fault's. Furthermore, we infer that the recurrence interval of Chijiaciwo Fault is 15ka BP, which is close to that of Dengdengshan Fault.
The latest event on Chijiaciwo Fault is later than the Dengdengshan Fault's, and the vertical displacement and the slip rate of a single event in late Quaternary are both larger than that of Dengdengshan Fault. Additionally, a 5-kilometer-long discontinuity segment exists between these two faults and is covered by Quaternary alluvial sand gravel. All these indicate that the activity of the Chijiaciwo Fault and Dengdengshan Fault has obvious segmentation feature.
The size of Chijiaciwo Fault and Dengdengshan Fault are small, and the vertical slip rate of 0.04~0.06mm/a is far smaller than that of Qilianshan Fault and the NW-striking faults in Jiuxi Basin. All these indeicate that the tectonic deformation of this region is mainly concentrated on Hexi Corrider and the interior of Tibet Plateau, while the activties of Chijiaciwo and Dengdengshan faults are characterized by slow slip rate, long recurrence interval(more than 10ka)and slow tectonic deformation.

Many NW-trending faults are developed in West Shandong. Cangshan-Nishan Fault,about 130km long,striking 310°～340°,dipping to SW and NE with dip angle 70°～80°,is the largest one among these faults. According to geomorphological characteristics and relationship between fault and Quaternary deposits,Cangshan-Nishan Fault can be divided into three segments: the western segment(Fangshan-Tianhuang segment),about 30km long,controlling the western margin of Qufu Basin; the middle segment in the bedrock area(Tianhuang-Ganlin segment),about 80km long,forming a valley and controlling evolution of Baiyan River; and the eastern segment(Ganlin-Cangshan segment),buried in the Quaternary basin,about 20km long.
The western segment(Fangshan-Tianhuang segment)appears as a linear scarp in the satellite images. Field investigation shows that the linear scarp is mainly composed of rock with 2～5m high in topography. On the northeast side of the scarp is mountains composed of Archaeozoic Taishan group gneiss,and on the south-west side is late Pleistocene alluvial fan. A lot of profiles reveal that the late-Pleistocene deposits(the thermoluminescence dating results)are dislocated by the fault. The fault cross sections near the Qufu city show it is a normal fault with high scarps. The highest scarp is 4.7m high and the normal vertical slip rate is 0.07mm/a. However,the fault cross sections near the Tianhuang Town show it is a reverse fault with high dip angle. The highest scarp is about 1.5m high, lower than that near the Qufu city. All these information indicate that the fault,from west to east,is changed gradually from normal feature to reverse feature,and the height of fault scarp is decreased gradually from west to east.
Based on reported results in this area,Cangshan-Nishan Fault is a left-lateral strike-slip hinge fault. The results presented in this paper suggest that the western segment is dominated by normal dip-slip with left-lateral strike-slip component,the middle segment is dominated by left-lateral strike-slip with reverse dip-slip component. As the axes of hinge fault,the middle segment is the most active segment of Cangshan-Nishan Fault. Besides Cangshan-Nishan Fault,a series of NW-trending faults are developed in West Shandong with weak activity since late-Pleistocene. Many moderate-strong earthquakes are related to these NW-trending faults. We thus think these NW-trending faults have capability of generating moderate-sized quakes.

Many NW-trending faults have been developed on the north of the eastern segment of Altyn Tagh Fault. The Tarwan Fault,about 10km long and striking NW on the whole,is the western segment of the largest Tarwan-Dengdengshan-Chijiaciwo Fault among these faults. The fault appears as a straight linear scarp in the satellite image and a geomorphic scarp of dozens of centimeters to 5 meters high,topographically. The scarp dips NE and is composed mainly of beds of early Pleistocene conglomerate and Holocene aeolian sandy soil. As revealed by a measured topographic profile,the scarp composed of Holocene aeolian sandy soil is about 5m high,and that of early Pleistoscene conglomerate is about 1m high. Field investigation and trenches excavated on the vertical scarp have revealed the Tarwan Fault is a thrust fault,striking NW and dipping SW.The Geogene mudstone is thrust over the early Pleistocene conglomerate,with a throw of 0.5m. The Holocene aeolian sand and late Pleistocene gravel layers overlying the fault are not dislocated. The hanging wall of the fault is Geogene mudstone with rich groundwater and well-developed vegetation. Due to the protection and control of sand movement with vegetation,aeolian sand was accumulated constantly and preserved,and as a result,the aeolian sand layer became higher gradually. The foot wall of the fault consists of a Gobi gravel layer of a few centimeters thick on the surface and hard cemented conglomerate of early Pleistocene under it,with groundwater and vegetation being undeveloped. Therefore,Holocene aeolian sand is only developed on the hanging wall of the fault,and there is no Holocene stratum developed in the footwall. The height of the scarp formed on the early Pleistocene conglomerate is far lower than that on the Holocene aeolian sand. These findings indicate that the topographic scarp composed of Holocene aeolian sand was produced by external dynamic process rather than faulting,and that the Tarwan Fault is an early-middle Pleistocene thrust fault.