The neotectonic activity is intense in the Taiwan Straits and the coastal area of South China. This region is one of the earthquake-prone areas of the world. In history, earthquakes of magnitude 6-7 occurred repeatedly in this region with a high recurrence rate. Therefore, this area has always been the focus of seismicity research and coastal earthquake prevention and disaster reduction. The exploration of active faults is the basis for seismic zoning, but the detection and identification of active faults in sea area are more difficult because of the coverage of sea water, which leads to a large number of “blind areas” in marine fault exploration for a long time. Seismic exploration methods are economical, suitable and efficient in detecting active faults in the sea area. This study compares the detection effect of different seismic sources.
In this study, geophysical exploration of active faults was carried out in the southeast Fujian uplift zone in the Taiwan Straits. A mini-multichannel seismic profile of GI gun source and sparker source at the same location was selected for comparative analysis and illustration. Five reflection interfaces(T₁—T₄, Tg)were interpreted on the GI gun profile, and five sets of seismic sequences(A—E)were classified. Six reflection interfaces(T'₁, T₁—T₄, Tg)were interpreted on the sparker source profile, and six sets of seismic sequences(A—D and E₁—E₂)were classified. Three basement faults and two shallow faults with small vertical extension were found, which are active since the late Pleistocene. Among them, the scale of fault F₁ is large, the displacement of the basement fault F₁ is 51ms, and the overall displacement of (T₁—T₄) in the sediments is 35ms. Faults F₂—F₅ are located on the continental side of fault F₁ and can be combined into grabens and horsts in forms, which are inferred to be the associated faults of Fault F₁. It’s found that basement faults can be identified by both GI gun profile and sparker source profile, while the small faults can only be identified by the sparker profile. At the same time, the depth of upper breakpoint on the sparker profile is shallower, and the latest fault activity can be traced back to the Holocene. The locations and geometrical shapes of the three basement faults are similar on the two profiles, but there are imaging differences in the formation shapes around the faults and the distribution patterns of the secondary faults due to the influence of resolution. The similarity of fault detection results shows the effectiveness of the two methods, while the difference of profile imaging shows the necessity of combined detection in practical work.
According to the comparison of the two kinds of data, the sparker profile reveals a finer shallow structure than the GI gun profile does, and the GI gun profile can obtain a clearer basement structure. Based on the fusion results of the two kinds of data, the structural attributes of fault F₁ are further analyzed and explained in detail in this paper, and the Fault F₁ is the result of the reactivation of a basement pre-existing fault in the late Pleistocene and is a depression-boundary fault with an activity pattern of extensional normal faulting, and it is considered in this paper to be part of the South China Binhai fault zone. Therefore, it is necessary to attach importance to the combination of multiple detection methods in marine seismic zoning and marine seismic hazard assessment in order to obtain more detailed fault information.

As the key area of interaction between land and sea, continental shelf is important for the tectonic evolution of continent, sea-land change, sea level eustacy and climate change. Due to the limits of different methods, the understanding of the chronology and potential geological information of the sediments on the continental shelf is not enough. The South China Sea, as the largest marginal sea of the West Pacific, is not only one of the most active areas of marine sedimentation in the world, but also the typical region of the interaction between land and sea. As the main sedimentary area of the East Asia, the South China Sea has received increasing academic research attention. At present, the researches mostly focus on the deep-sea sediments because they are continuous and can record stable signals, even though the relative slow deposition and low resolution. Comparatively, the shallow continental shelf deposits with faster sedimentary rate and higher resolution can provide important geological materials for studying the high-resolution chronology and paleoenvironment. However, the sedimentary signals recorded by the continental shelf sediments are unstable and even missing due to the turbulence of the sedimentary environment of the continental shelf. There are relatively few studies on the continental shelf sediments of the South China Sea, especially the high-resolution chronology of cores, thus limiting the understanding of tectonic and climate evolution of the South China Sea. In order to better constrain the geological chronology of the Late Pleistocene continental shelf sediments in northern South China Sea, study the paleoenvironmental signals in the continental shelf sediments and discuss the driving mechanism of the climate changes in East Asia and provide the chronological framework for the study of marine active tectonics in the South China Sea, the comparison between magnetic susceptibility and Marine Oxygen Isotope based on microscopic paleonotological fossils and carbon isotopic age(¹⁴C)was studied on the Core DG in this paper. Additionally, the results of sediments color and pollens were used to study the paleoclimatic implications. The results of magnetic susceptibility suggest that the chronology of the sediments of Core DG can be constrained from MIS 1 to MIS 9, with the age of the bottom being about 300ka. The relative high and low values of magnetic susceptibility correspond to interglacial and glacial periods, respectively. This is consistent with the paleoclimatic signals evidenced by the changes of pollen and color parameters in the DG core sediments. Therefore, we suggest that the magnetic susceptibility of continental shelf sediments can be affected by the changes of climate. During glacial periods, the relative cold weather, shallow water and increased transportation distance of the sediments resulted in the enhanced oxidation and the formation of minerals with weak magnetic susceptibility(such as hematite), thus the magnetic susceptibility decreased and the redness increased in the sediments. However, during interglacial periods, the relative warm and wet climate, together with the decreased transportation distance of the sediments, led to the formation of minerals with strong magnetic susceptibility(such as magnetite), thus the magnetic susceptibility enhanced significantly and the redness decreased in the sediments. Therefore, the variations of the magnetic susceptibility in the continental shelf sediments in the northern part of the South China Sea can reflect the glacial-interglacial cycles in the East Asia since the late Pleistocene. In conclusion, as a relative dating method used in the unconsolidated sediments in the late Quaternary, the comparison between magnetic susceptibility and Marine Oxygen Isotope is applicative and reliable in constraining the chronology of the Late Pleistocene continental shelf sediments in northern South China Sea, thus providing a new reference for studying and correlating the continental shelf sediments, which can be used reasonably in the Quaternary chronology.

The deformation pattern in the northeastern margin of Tibetan plateau is characterized by NE compression, clockwise rotation and eastward extrusion, forming the NNE trending dextral strike-slip faults which further divide the region into several sub-blocks. The deformation of Qaidam secondary block is dominant by northwestward extrusion and rotation, which is controlled by the Elashan and East Kunlun faults. However, the deformation style of Dulan area, the junction of these two faults, remains unclear. We discovered a new active fault zone with a length of 60~70km west to Elashan Fault during our recent field geological survey around Dulan area, named Xiariha fault zone(XFZ), which is a dextral strike-slip fault zone trending NW, consisting of the Xiariha and Yingdeerkang faults. According to the remote sensing interpretation and field investigation, it is found that the Xiariha fault zone showed distinct linear characteristics, reverse scarp, sag pond and ridge dislocation on the satellite images and displaced multi-levels of alluvial fans and river terraces. According to previous studies, the exposed age of T1 terraces is Holocene in the Elashan area, which is located at east of Dulan. During the field investigation, we used the unmanned aerial vehicle(UAV)to get the fine geomorphology features along the XFZ. Also, to define the active era, we tried to find the fault section of the XFZ that could provide the information of the contact between the fault and late Quaternary strata. Based on the high-resolution DEM obtained by UAV, the offset of T1 is about 2.5m, indicating its activity in Holocene compared with the Elashan area. Along the XFZ, the fault displaced late Quaternary strata revealed on the section. The geomorphic features and fault section show that the XFZ is a late Pleistocene to Holocene active fault. The Dulan area is located at the convergence of East Kunlun Fault and Elashan Fault, the southeastern end of Qaidam secondary block, which is affected by the regional NE and SW principal compressive stress and shear stress. Under this circumstance, the Qaidam block is experiencing extrusion and rotation and there are a series of NW-trending dextral strike-slip faults parallel to the Elashan Fault and EW-trending sinistral strike-slip faults parallel to the East Kunlun Fault, such as Reshui-Taosituo River Fault, developed in the Dulan area. Therefore, we suggest that the Xiariha Fault and the nearly EW trending, Holocene sinistral Reshui-Taosituo River Fault adjust the extrusion rotation deformation jointly at the southeast end of the Qaidam block under the control of the Elashan Fault and the East Kunlun Fault, respectively. Meanwhile, the new discovery of Xiariha Fault and its activity in Holocene is not only of great significance to understand the regional tectonic deformation model, but also leads to a great change in the understanding of regional seismic risk because of its capabliliby of generating strong earthquakes. Therefore, it is urgent to carry out further research work in this area, improve the understanding of regional strain distribution mode, and provide reference for regional seismic safety issues.

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.

Meso-Cenozoic inversion structures developed in northern Songliao Basin represent the third tectonic evolution stage of the basin following the rifting stage and the depression stage of thermal cooling. The paper collects systematically 30 regional seismic reflection profiles laid out to cover the Da'an-Dedu Fault and its adjacent14 3-D seismic projects, and on this basis, accurately tracks and interprets a total of seven seismic reflection horizons of T₀₆, T₁, T₁₁, T₂, T₃, T₄ and T₅. At the same time, geological age of key reflection horizons is re-determined based on 52 boreholes data, the distribution characteristics and pattern of different periods are analyzed, and the geometric configuration and deformation characteristics and mechanisms of Meso-Cenozoic inversion structures developed in the northern Songliao Basin are discussed in particular. The study concludes that the inversion structure is the main deformation model of Da'an-Dedu Fault in the late Mesozoic and early Cenozoic, which coincides to the geometric shape and deformation mechanism of the "thrust-fold" structures.
Based on the experimental shallow seismic exploration results of section line No.10 and No.11 in the research area, we find that the small faults, which are widely developed on the top of anticline and disconnect the reflection interface of T₀₆, represent the latest activity of Da'an-Dedu Fault, and the deformed layer formed in mid-Pleistocene may indicate the latest activity time of Da'an-Dedu Fault, which is mid-Pleistocene.
In addition, according to the study on shallow seismic exploration results, modern earthquake activity and focal mechanism solutions, we strongly believe that the latest activity of "thrust-fold" inversion structures of the Da'an-Dedu Fault has an obvious effect on the near surface reflection layers, which offsets the lower-middle Pliocene and controls the moderate-strong earthquake activity of the research area and the adjacent areas. These structures should be regarded as one of the most important and typical seismogenic structures in the interior of Songliao Basin and in the Northeast China region. Based on this, we can understand scientifically the deformation process of the interior of Songliao tectonic block through the research of structural deformation of Da'an-Dedu Fault developed inside the block after the late Cenozoic era, and the future earthquake activities controlled by the Da'an-Dedu Fault.

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.

On July 22,2013,an earthquake of M_S 6.6 occurred at the boundary between Minxian County and Zhangxian County,Gansu Province of China. Many landslides were triggered by the earthquake and the landslides were of various types,mainly in falls,slides,and topples occurring on loess cliffs,and also including soil deep-seated coherent landslides,large-scale soil avalanches,and slopes with cracks. Most of the landslides were distributed in an elongated area of 250km²,parallels to the Lintan-Dangchang Fault, with about 40km in length and the largest width of 8km. Landslides occurrence shows obvious difference along the central line of the elongated area,corresponding to different characteristics of different segments of the seismogenic fault. The elongated landslides main distribution area and the location of the epicenter indicate that the direction of the fault rupture propagation is from southeast-east to northwest-west. Finally,two probable reasons causing the horizontal distance of about 10km between the central line of the elongated area and the Lintan-Dangchang Fault are presented.

On July 22,2013,the Minxian-Zhanxian M_S 6.6 earthquake occurred at the central-northern part of the South-North Seismic Belt. In the area,complicated structural geometries are controlled by major strike-slip fault zones,i.e.the Eastern Kunlun Fault and the Northern Frontal Fault of West Qinling. The distribution of related seismic disasters,namely,the ellipse with its major axis trending NWW,is in good accord with the strike of the Lintan-Tanchang Fault. Severe damages in the meizoseismal area of the Minxian-Zhangxian M_S 6.6 earthquake are located within the fault zone. So it is considered that the earthquake related damages are closely related to the complicated geometry of the Lintan-Tanchang Fault,and it also indicates that the earthquake is the outcome of joint action of its secondary faults. Based on field investigations,and by integrating the results of previous studies on active tectonics,structural deformation and geophysical data,it can be inferred that the southward extension of the Northern Frontal Fault of West Qinling and the northeastward extrusion of the Eastern Kunlun Fault in the process of northeastward growth of Tibetan plateau are the main source of tectonic stress. Basic tectonic model is provided for strong earthquake generation on the Lintan-Tanchang Fault.

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.

The co-seismic rupture is one of the important contents in active tectonic mapping.As the late Quaternary landform is a basic recording medium for the recent deformation of active fault,such as the co-seismic rupture,it is quite useful to acquire the activity information of the active fault from various landforms.We implemented a field work along the southeastern segment of the Xianshuihe Fault,mapped the rupture and excavated some trenches.The preservation characteristics of the surface rupture of the 1786 Moxi earthquake were discussed for the glacial area of the Tibetan plateau,the fluvial and flooding area and seriously eroded area at the margin of the Tibetan plateau,respectively.The cracks and offsets were preserved continuously in the glacial landforms such as the moraines and glacial outwashes along Kangding to Yajiageng segment.As the landforms in the fluvial and flooding area were unstable under strong erosion and rapid deposition,the surface rupture can be discovered in the trenches excavated in Yuejinping village and Ertaizi village with gaps for some previous earthquakes.There was no deposition from the erosion landform to record the surface rupture.We can only infer the earthquake effected area and the ruptured fault from the indirect relationship between landslides and the earthquake strong motion or the fault rupturing.Based on the integrated analysis with the geometry and tectonic setting of the southeastern segment of the Xianshuihe Fault,the Kangding-Tianwan segment of the Xianshuihe Fault was taken as the seismogenic fault of the 1786 Moxi earthquake,and the total length of the rupture is about 80 kilometers.

No earthquake greater than M6 has been documented on the Yilan-Yitong Fault,and no trace of activity since the late pleistocene has been seen either at the northeastern section of the famed Tanlu grand fault zone in eastern China.Thus this fault is recognized active in the early Quaternary and capable of generating moderate quakes.By analyzing high-resolution satellite images and field work,a 70km-long geomorphic scarp in Tonghe County of Heilongjiang Province and a 10km-long geomorphic scarp in Shulan County of Jilin Province were discovered.The scarps are 1～2m high and offset the young terraces.Subsequently,the trench at Tonghe County revealed fault displacement which almost reaches the surface.The uppermost stratum dislocated by the fault is dated to be 1730±40 years B.P.Analysis of geomorphic feature of the fault scarp and the trench profile suggests that an M≥7 paleoearthquake occurred along the fault since 1730±40 B.P.The trench at Shulan County reveals the faulted late Pleistocene stratum covered by stratum dated to be 2360±40 years B.P.All these data suggest that some segments of Yilan-Yitong Fault are active since Holocene and M7 earthquake occurred.So,further detailed research will be necessary to determine the range of the latest activity of this fault,the time of the rupture and recurrence intervals of major earthquakes.These data will be of great significance for earthquake zonation and assessment of seismic risk in this region.

The slip rate decreased at Subei,Shibaocheng and Shulehe regions on the eastern segment of Altyn Fault,the regions called as "singularity points". Subei is one of "singularity points" on the eastern segment of Altyn Fault,and the north of Yemahe Fault in the northeast of Subei is the fault we study in this paper. The fault is located in the northeast of Yemahe Basin. It starts at Erdaogou gully in the east and ends at Niujuan gully,extending along the Yema mountain front and parallel to the Altyn Fault in the direction of NEE on the whole. It separates Sinian from Quaternary gravel layer. There are plenty of left-lateral slip-strike and thrusting geomorphologic phenomena and exposed stratigraphic sections on the sides of gullies. Ridges and gullies are dislocated synchronously.Through more than one month investigation,we obtained the distribution and the geological and geomorphologic characteristics of the fault,measured a series of left-lateral slip gullies,ridges and thrust scarps and got the relevant data. Some samples are also collected. The left-lateral slip of gullies is distributed from 1.3m to 175m,and the height of thrust scarps is from 0.95m to 8.53m. The horizontal averaged slip rate of the fault is calculated to be 1.27?0.18mm/a,and the averaged thrusting rate is 0.4?0.07mm/a. This fault,together with the Danghenanshan thrust fault at its south,resolved part of the movement components of the eastern segment of Altyn Fault.

Geo-slicer method,a newly developed technique for detecting active fault,is designed to take a slice of unconsolidated Quaternary strata whose texture and structure are not destroyed. The Sanhe-Pinggu M8 earthquake of 1679 is the biggest one recorded in Beijing area. The macroscopical epicenter is located around Pangezhuang Village,Xiadian Town,Hebei Province. We successfully applied the geo-slicer method to detecting the rupture of this earthquake near its epicenter. Through our test research,we gained the following knowledge: 1)the detailed deposit structure of the unconsolidated strata can be kept in the geo-slicer; 2)the power unit should be selected to fit to different site conditions,and for Beijing area,a power unit with "grab+vibrant hammer" is better than that with "crane+hammer" ; 3)there is some shortening due to the vibration of the power,but the shortening is generally less than 5%. Moreover,synthesizing the information from the geo-slicers and trench,we found two earthquake events. One is the 1679 earthquake and the other is the one before the 1679. The vertical seismic displacements are 1.4m and 1.2m,respectively.

The newest active time and segmentation of the fault are of special significance in the safety evaluation of major engineering projects.This paper discusses the active times and segmentation characteristics of the Guanguanling Fault zone through interpreting aerial photos,field investigation,topographic and geomorphic surveys and analysis of trench logs on paleoearthquake in connection with the study of the geological and seismologic problems in Heishanxia project of the Huanghe River.The Guanguanling active fault zone lies on the northeastern margin of the Qinghai-Tibet block.It is part of the Zhongwei-Tongxin arc active fault zone,striking near EW generally,with a total length of about 60km.It consists of 5 discontinuous secondary faults arranged in left step en echelon,namely,Jingtaixiaohongshan(F_1-1),Guanguanling(F_1-2),Shajing(F_1-3),Zhongweixiaohongshan(F_1-5)and Qingshan-Gushanzi(F_1-4),respectively.Since Late Quaternary,the fault is characterized with intense sinistral strike-slip and compressional thrust and has offset a series of ridges and small gullies and terraces.At the same time,fault scarps were developed along the fault zone.The study reveals that the latest earthquake occurred 700～1200a BP,the largest displacement took place in Guanguanling,and the maximum horizontal sinistral displacement reaches 6m since Holocene.

The Kalpintag nappe is located at the southwestern foot of the Tianshan Mountains,consisting of several rows of NE-to EW-trending fold-reverse fault zones.This paper demonstrates the activities and slip rate of the frontal faults of the first to third row fold-reverse fault zones located to the west of the Piqiang-Bachu phosphorite mine.The newly-found evidence shows that the front of each fold-reverse fault zone is composed of several faults of typical reverse fault type.The faults with newest activity are located at the forefront of the fold-reverse fault zones,and the active period of the faults is late Pleistocene-Holocene.They dissect the T₀,T₁,T₂ and T₃ terraces,resulting in fault scarps of different heights.According to the in-situ measurement of the fault scarps and the dating data of the relevant samples,it is estimated that the amount and rate of vertical displacement along the faults since the formation of the T₀ terrace are 0.9～1.1m and 0.53～0.65mm/a,respectively,while the amount and rate of the corresponding crustal shortening are 1.93～2.56m and 1.14～1.52mm/a,respectively.Similarly,it is estimated that the amount and rate of vertical displacement since the formation of the T₁ terrace are 1.4～1.8m,and 0.36～0.46mm/a,with the corresponding crustal shortening of 3.00～3.86m,and shortening rate of 0.77～0.99mm/a.The vertical displacement amount and rate since the formation of the T₂ terrace are about 2.1～3.0m and 0.31～0.45mm/a,respectively,and the amount and rate of the corresponding crustal shortening are 4.50～6.98m and 0.67～1.04mm/a.The amount and rate of vertical displacement since the formation of the T₃ terrace are 3.4～4.2m and 0.28～0.35mm/a,and the amount and rate of the corresponding crustal shortening are 7.29～9.22m and 0.61～0.77mm/a,respectively.Based on the obtained amount and rate of crustal shortening since the formation of T₀ terrace,the total amount and rate of crustal shortening of the Kalpintag nappe since 1.7ka can be estimated to be 9.65～12.80m and 5.68～7.53mm,respectively.

Growth strata (i.e. progressive unconformities) are linked to a particular structure at depth and a record for different tectonic and sedimentation processes. they locate in foreland basins on the fronts of fold and thrust belts and exhibit extremely varied attitudes. The inherent synchroneity of growth strata and coupled fold or fault activity make growth strata crucial to interpret fold-and-thrust geometry and kinematics. On the balanced cross-section the sequences of growth strata have characteristic wedge-shaped sedimentation. In coeval depositional systems, fault-bend folding, fault-propagation folding and detachment folding are interpreted as the dominant mechanisms. The other modes of folding are recognized later in the 1980s,for example, Trishear folding and Chester and Chester folding, and so on. Though several types of theoretical behavior are expected, all growth strata can be grouped into two fundamental mechanisms: hinge migration and Limb rotation. Growth strata result from a simultaneous interference of several processes such as tectonics, sedimentation and erosion. The interplay between tectonic and surface processes has been shown to constrain the evolution of orogens through a feedback mechanism, the competition between tectonic uplift and shortening, syntectonic sedimentation rate and syntectonic erosion rate controls the final shape and the occurrence and geometries of fault breakthrough in thrust-related anticlines. According to variety of limb and hinge, synsedimentary wedge, variety of strata occurrence and thickness and regional geological setting, growth strata can be identified. In the future, the study of thrust-related folding processes within folds and thrusts belts will be developed by multi-models and ways. Synchroneity and continuity of growth strata and coupled fold or fault activity can be depicted accurately. Based on the present work and good examples of growth strata, paleomagnetic stratigraphy can provide some important information about chronology and tectonic process. Through reviewing briefly the importance, geometry and kinematics of growth strata, we conclude that the Sikouzi section should be a molasses basin occurring in the front of thrust-fold mountain belt where there exist growth strata and progressive unconformities. However,detailed investigation should be done on this in the future.

The Kalpintag Fault locates at the most forefront of Kalpintag nappe tectonics, and can be separated into eastern and western segments by Piqiang Fault. Six large trenches are excavated along the western segment and four paleoearthquakes can be distinguished in the three trenches of them. The first paleoevent occurred about 12ka BP, the second event occurred about 8.6ka BP, the third event occurred about 5ka BP,and the last event occurred after (1.73±0.15) ka BP, which probably is the Xike'er M6.8 earthquake in 1961 AD. The four paleoevents are characterized by 3～4ka quasi-periodic recurrence interval. The Kalpintag nappe structure are composed of 5～6 rows of fold-reverse fault zones. The faults with the latest activity are located at the forefront of the fold-reverse fault zones with 10km spacing between each fault. The north-dipping and listric style fault surfaces merged into the detachment surface in the deep along the bottom of Cambrian at 6～10km depth. The field investigation discovered that earthquake ruptures and paleoearthquake traces can be found not only along Kalpintag Fault but also along other faults, but the rupture length and seismic slip are smaller than that formed by an M≥7 earthquake. Although five paleoearthquakes since 14ka BP are obtained along western segment of Kalpintag Fault, some events are probably missed because of less trenches and dating samples. Many problems such as magnitude of these events, seismogenic fault and their rupture zones formed by one or several events await study in the future.

The Kalpintag fold nappe is located at the northwestern foot of the Tianshan Mountains. Since Cenozoic, owing to the Indian-Eurasian collision, the Mesozoic fold structures of Tianshan have been rejuvenated, uplifted and pushed northward and westward. As a result, several rows of fold-reverse fault zones have been progressively formed within the foreland basins. This paper describes in detail the Cenozoic deformation features and propagation of the fold-reverse fault zone on the west of the nearly south-north-trending Piqiang fault zone. The results show that the Cenozoic deformation of the nappe was characterized by wavy differential uplift, and this has caused the successive formation of the fold-reverse fault zone from the southern side of the Tianshan Mountains to the Tarim Basin. Among them, the early-formed folds are close to the Tianshan Mountains, while the latter-formed folds are close to the Tarim Basin, indicating the general tendency of northward propagation of the fold-reverse fault zone during their formation process. The distance of propagation may reach up to 76km. Moreover, the front of individual fold-reverse fault zone consists of several fault strands, which are associated with folds and have different ages of formation and time of recent activity. The early-formed faults are close to the Mountain side and the latter-formed close to the basin, indicating the northward propagation of the frontal faults of the individual fold. The distance of propagation is about 100～500m. The mechanism of the propagation of the fold-reverse fault zone is discussed in this paper as well.

Kalpin thrust tectonic is an active reverse fault fold zone at the southwestern Tianshan front piedmont, it consists of five to six rows of arc fold zones which are formed by Cambrian-Quaternary sedimentary rocks. The major morphology of the anticline is multiple box-shaped or asymmetry inclined, mostly, and it is similar to that of fault-bend fold and fault-propagation fold. Depending on the seismic reflection surveys data, the reverse faults on the front of the nappe in Kalpin thrust tectonic zone form an integrate detachment surface in the deep along the gypsum stratum in Cambrian. The depth of the detachment is shallower in the southeast and deeper in the northwest. The depth of the detachment fault is deeper in the west part (about 9km deep) and shallower in the east part (about 5km deep) of the Piqiang fault. In the middle part of the Kalpin reverse fault-fold zone, we have made two balanced cross-sections at the two sides of Piqiang fault. On the two geological cross-sections, we construct the structure mode at depth using fault-bend fold or fault-propagation fold model. The length of the two sections is 73km and 78km, respectively. The restored sections yield a crustal shortening of 40km to 45km, the shortening rate is 33% and 37%, respectively. Calculating the long-term shortening rate from these two across-sections is difficult, because the time of initiation of deformation is poorly known. Geological evidence suggests that most of the shortening began in the beginning of the deposition of the thick conglomerate unit in lower Quaternary. If the initiation time is about 2.5Ma, the shortening rate of Kalpin thrust tectonic zone is 15.4～17.3mm/a.

On the basis of 1/10,000 active fault mapping in Fuzhou Basin, interpretation of aerial photos and detailed field investigation, 11 sites on six faults in the basin were selected for exploratory trenching. The main results of trenching are as follows:(1)Two trenches were dug across the Hutou-Miaopu Fault. One of the trenches reveals a fault plane, which is developed in lava bed and covered by Quaternary strata with an age of 75?6ka B.P. The other trench reveals that a series of joints are developed in tuff bed, but they do not offset the overlying strata of 119?10ka in age. These facts may indicate that the fault had ceased moving since late Pleistocene.(2)Two trenches were excavated across the Gushan Fault. No fault plane can be identified in one of the trenches, but the second trench reveals a minor fault plane, which is developed in granite and does not offset the overlying strata of 100?9ka in age. It can be concluded, therefore,that the fault had also ceased moving since late Pleistocene.(3)Two trenches were excavated across the Wuhushan Fault. In both trenches, the relationships between the volcanic rocks and Quaternary deposits, as well as the fault planes in volcanic rocks and overlying Quaternary deposits are well exposed. A series of minor fault planes developed in granitic rocks are well exposed in one trench, and these minor faults do not offset the overlying strata of 98?8.3ka in age. It is postulated, therefore,that the fault might have ceased moving since the early stage of late Pleistocene.(4)The micro-gemorphological expression of the Minhou-Nanyu Fault can be distinctly traced along the fault strand. A fault trough is observed at Heshangsi Temple, where two trenches were excavated to identify the two faults on the eastern and western sides of the trough. The trench logs show that the fault planes that are developed in granitic rocks do not offset the overlying Quaternary deposits of 29?2ka in age. Obviously, the Minhou-Nanyu Fault had ceased moving since the late stage of late Pleistocene.(5)One trench was excavated across the Tongkou-Hongshanqiao Fault. The trench log reveals two fault planes, which dislocate the same bed of Quaternary strata and are covered by the younger bed. The age of offset bed is dated to be 193?16ka B.P, and that of the overlying bed is 100?9ka. It is suggested, therefore, that the fault had also ceased moving since late Pleistocene.(6)A 4-5 meters deep trench was excavated across the Bayishuiku-Shanggan buried fault. Geophysical prospecting data suggested that the fault probably passes the trenching site. However, no fault is found in the trench, and the Quaternary deposits here are nearly horizontal. The age of bottom deposits is dated to be 39?3ka B.P. It seems that the Bayishuiku-Shanggan Fault had ceased its activity since the late stage of late Pleistocene. The afore-mentioned conclusions are merely drawn from the results of trenching, and more detailed study is needed in the future.

The Western Jiuquan (Jiuxi) Basin is located in the westernmost part of the Hexi Corridor. The basin is bounded by the Qilian Mountain fault on the south, by Alytn Taugh fault on the north, and by Jiayuguan fault on the east, respectively. The Hexi Corridor is one of the seismically active regions in western China. According to historical records, a large number of strong earthquakes had occurred in this area. Recently, we have discovered three Holocene active faults through the interpretation of aerial photos and field investigation in the Jiuxi basin. These three faults are called Xinminpu, Yinwashan and Yumen faults, respectively. The Xinminpu fault is a Holocene thrust fault, which is 17km in length, striking 315°and dipping southwest, located in the northern part of the basin. A fault scarp of 14m height was developed on the hanging wall of the fault, and it is superposed by the newly formed fault scarp with free surface. The rate of vertical motion along the fault is determined to be 0.24mm/yr. The Yinwashan fault is a Holocene thrust fault located on the alluvial fan at the eastern piedmont of the Yinwashan Mountain, striking 315°with a length of 17km and dipping southwest. The rate of vertical motion along the fault is determined to be 0.18mm/yr. Two Holocene paleoearthquake events have been identified through trenching on the fault. The first event occurred 10.64±0.83ka B.P., while the second event occurred between 4.09±0.31ka B.P. and 8.22±0.63ka B.P. The Yumen fault is also a Holocene thrust fault, which is nearly EW-striking and south dipping, located on the alluvial fan at the northern piedmont of the Qilianshan Mountain. A fault scarp of less than 2m height was developed along the fault. The fault scarp was perhaps produced by a historical earthquake. The rate of vertical motion along the fault is determined to be 0.25mm/yr. Two Holocene paleoearthquakes were revealed by trenching on the fault. The first earthquake occurred at 3.05±0.24 ～3.20±0.25ka B.P. The second occurred after 3.05±0.24ka B.P. As mentioned above, all the three Holocene faults belong to thrust fault, and thus no obvious horizontal displacement can be observed along the fault. This may indicate that this area is dominated by compressional deformation. According to historical records, the Jiuquan earthquake of 756 A.D. is the latest historical earthquake occurred in this area. It is postulated that the Xinminpu fault or Yumen fault would be ruptured during this earthquake, but currently we are unable to determine which fault was ruptured by this earthquake on the basis of available dating data. The ages of paleoearthquakes and the characters of surface ruptures along the three faults suggested that the three faults were activated independently or sometimes in cluster.

The Zhongwei-Tongxin fault zone is one of the arcuate active fault zones in northeastern margin of Tibetan plateau. An earthquake of M =7 1/2 occurred on the middle segment of the fault zone in 1709 A.D. The structures of the fault zone are complicated and composed of a series of secondary faults. The fault zone can be divided into three segments according to the differences in the style of movement, strength and time of activity of the secondary faults. The study of the behavior of paleo-seismicity on the fault zone, therefore, is of great significance to better understanding of the segmented rupturing and the assessment of future seismic risk. The western segment of the fault zone is nearly E-W-trending with a total length of about 60km, most of which is covered by wind carried sand. The recent activity of the faults on this segment is displayed most distinctly at Xiaohongshan area. The middle segment trends NWW with a length of 55km. This segment is the most active one among the three segments of the fault zone. A series of streams, terraces, ridges and alluvial fans were sinistrally offset along the fault. The average left lateral-strike slip rate since Holocene is 3.58mm/a. The eastern segment changes from NW-trending to NNW-and S-N-trending, having a length of about 40km. This segment is located in the compressional area of Zhongwei-Tongxin left-lateral strike slip fault zone, where folding deformation is predominant and the fault is activated weakly. Seven trenches were excavated recently along the fault zone. Five of them are located on the middle segment and the rest on the western segment. Combining new data from the seven trenches and results obtained before, we discuss in this paper the recurrence behavior of paleoearthquakes on Zhongwei-Tongxin fault zone. The seven trenches have revealed six paleoearthquake events of the past 14 000 years along Zhongwei-Tongxin fault zone. One of them occurred in late Pleistocene and had ruptured the whole fault zone, while the others all occurred in Holocene and had ruptured only the middle or western segment. The 1709 Zhongwei earthquake of M =7 1/2 had ruptured only the middle segment of the fault zone. We postulate, therefore, that the magnitude of paleoearthquake that ruptured the middle or western segment of the fault zone should be about 7 1/2,while that of the event ruptured the whole fault zone should be about 8. In addition, we find that the temporal distribution of paleoearthquakes on the Zhongwei-Tongxin fault zone was neither uniform nor evidently clustered.

The 240km long Haiyuan fracture zone is a typical active fault in the inland of China. The 1920 Haiyuan earthquake (M_S8.6) has made the whole fault offset sinistrally. Our recent research on the large scale geological-geomorphological mapping and 3-D trench excavation at Gaowanzi,Haiyuan fault has revealed that at least 7 paleoearthquakes have been occurred since Holocene. And we have also studied the time intensity distribution of these events. Except the earthquake of 1920,these events have their ages about (10004±3196),(6689±169),(6120±505),(4208±577),(2763±372),(1005±465) and 30a,respectively,and the recurrence interval between two adjacent events is (3315±3200),(561±532),(1920±766),(1425±686),(1578±595) and (980±465)a,respectively. It shows that recurrence of these events is not uniform. At least 4 events comply with the Quasi periodic occurrence model and their average recurrence interval is (1641±207)a while the former 3 events and the later 2 events have the possibility of complying with the nonquasi-periodic occurrence model. This implies that the fault activity has the stage feature in the time distribution,that is,it complies with different occurrence models in different period. We have obtained the horizontal displacements of events Ⅲ,Ⅳ,Ⅴ,Ⅵ,Ⅶ. They are (5.6±2.3),(1.5±1.1),(1.5±1.1),(2±1) and (7±0.5)m,respectively. It indicates that the intensity distribution is also not uniform. The intensity of event Ⅲ is nearly the same as that of event Ⅶ while that of other events is much smaller. This suggests that the characteristic slip of the Haiyuan fault is graded,that is,large characteristic earthquakes occurred on the master segments while relatively small ones occurred on the secondary segments. The recurrence interval of the large earthquakes which have nearly the same intensity as that of 1920 earthquake is about 6000a since middle Holocene while that of small earthquakes with 1～2m horizontal displacement is 1000～2000a. There are 3 events whose displacement is 1～2m occurred between these two large earthquakes. So we estimate that the next earthquake is a relatively small one with a horizontal displacement of 1～2m.