Longshou Shan, located at the southern edge of the Alxa block, is one of the outermost peripheral mountains and the northeasternmost area of the northeastern Tibetan plateau. In recent years, through geochronology, thermochronology, magnetic stratigraphy and other methods, a large number of studies have been carried out on the initiation time of major faults, the exhumation history of mountains and the formation and evolution of basins in the northeastern Tibet Plateau, the question of whether and when the northeastward expansion of the northeastern Tibet Plateau has affected the southern part of the Alxa block has been raised. Therefore, the exhumation history of Longshou Shan provides significant insight on the uplift and expansion of the Tibetan plateau and their dynamic mechanism. The Longshou Shan, trending NWW, is the largest mountain range in the Hexi Corridor Basin, and its highest peak is more than 3 600m(with average elevation of 2800m), where the average elevation of Hexi Corridor is 1 600m, the relative height difference between them is nearly 2200m. This mountain is bounded by two parallel thrust faults: The North Longshou Shan Fault(NLSF)and the South Longshou Shan Fault(SLSF), both of them trends NWW and has high angle of inclination(45°~70°)but dips opposite to each other. The South Longshou Shan Fault, located in the northern margin of the Hexi Corridor Basin, is the most active fault on the northeastern plateau, and controls the uplift of Longshou Shan.Due to its lower closure temperature, the lower-temperature thermochronology method can more accurately constrain the cooling process of a geological body in the upper crust. In recent years, the low-temperature thermochronology method has been used more and more in the study of the erosion of orogenic belts, the evolution of sedimentary basins and tectonic geomorphology. In this study, the apatite (U-Th)/He(AHe) method is used to analyze the erosion and uplift of rocks on the south and north sides of Longshou Shan. 11 AHe samples collected from the south slope exhibit variable AHe ages between~8Ma and~200Ma, the age-elevation plot shows that before 13~17Ma, the erosion rate of the Longshou Shan is very low, and then rapid erosion occurs in the mountain range, which indicates that the strong uplift of Longshou Shan occurred at 13~17Ma BP, resulting in rapid cooling of the southern rocks. In contrast, 3 AHe ages obtained from the north slope are older and more concentrated ranging from 220Ma BP to 240Ma BP, indicating that the north slope can be seen as a paleo-isothermal surface and the activity of the north side is weak. The results of thermal history inverse modeling show that the South Longshou Shan Fault was in a tectonic quiet period until the cooling rate suddenly increased to 3.33℃/Ma at 14Ma BP, indicating that Longshou Shan had not experienced large tectonic events before~14Ma BP.
    We believe that under the control of South Longshou Shan Fault, the mountain is characterized by a northward tilting uplift at Mid-Miocene. Our results on the initial deformation of the Longshou Shan, in combination with many published studies across the northeastern margin of the Tibetan plateau, suggest that the compression strain of the northeastern margin of the Tibetan plateau may expand from south to north, and the Tibetan plateau has expanded northeastward to the southern margin of the Alxa block as early as Mid-Miocene, making Longshou Shan the current structural and geomorphic boundary of the northeastern plateau.

The horizontal movement of the Helan Shan west-piedmont fault is important to determination of the present-day boundary between the Alashan and North China blocks as well as to the exploration of the extent of the northeastward expansion of the Tibetan plateau. Field geological surveys found that this fault cuts the west wing of the Neogene anticline, which right-laterally offset the geological boundary between Ganhegou and Qingshuiying Formations with displacement over 800m. The secondary tensional joints (fissures)intersected with the main faults developed on the Quaternary flood high platform near the fault, of which the acute angles indicate its dextral strike slip. The normal faults developed at the southern end of the Helan Shan west-piedmont fault show that the west wall of this fault moves northward, and the tensional adjustment zone formed at the end of the strike slip fault, which reflects that the horizontal movement of the main fault is dextral strike slip. The dextral dislocation occurred in the gully across the fault during different periods. Therefore, the Helan Shan west-piedmont fault is a dextral strike slip fault rather than a sinistral strike slip fault as previous work suggested. The relationship between the faulting and deformation of Cenozoic strata demonstrates that there were two stages of tectonic deformation near the Helan Shan west-piedmont fault since the late Cenozoic, namely early folding and late faulting. These two tectonic deformations are the result of the northeastward thrust on the Alashan block by the Tibet Plateau. The influence range of Tibetan plateau expansion has arrived in the Helan Shan west-piedmont area in the late Pliocene leading to the dextral strike slip of this fault as well as formation of the current boundary between the Alashan and North China blocks, which is also the youngest front of the Tibetan plateau.

Fault slip rate is one of the most important subjects in active tectonics research, which reveals the activity and seismic potential of a fault. Due to the improvement of dating precision with the development of dating methods, Holocene geological markers, even the young markers of thousands or hundreds years old, are widely used in fault slip rate calculation. Usually, in strike-slip fault slip rate calculation, there are two types of uncertainties. The first is correspondence of the offset and accumulation time; the second is the lateral erosion of the accumulated offset. In this paper, we suggest that the effect of lateral erosion of the accumulated offset should be removed. We also propose a new method for determining slip rate of strike-slip fault—the differential method. According to analyses of river terrace evolution and displacements accumulation, terrace heights (relative height above river), corresponding ages and measured offsets on the terraces are correlated to each other. We could use the terrace height, corresponding ages and the measured offsets to calculate the offsets that could be used to obtain the fault slip rate. Usually, the heights, ages and offsets of at least three terrace levels are needed in this method. If the terrace height is graded in order, the lateral erosion to each terrace is almost the same. Consequently, direct difference of offset and corresponding ages of the terraces could be used to calculate the fault slip rate. This kind of differential method could avoid the uncertainties from the lateral erosion in fault slip rate determination. By applying the differential method, we got the revised slip rates of 4.7～8.8mm/a on the Altyn Tagh and Kunlun Faults. These low slip rates could fit previous geodetic and geological fault slip rates, shortening rates as well as the millennial recurrence intervals of strong earthquakes along the major segments of these faults.

Interactions of two global-scale geodynamic systems control Cenozoic tectonic evolution of continental eastern Asia: the collisional and convergent system between Indian and Eurasian plates, the subduction and back-arc extensional system along the western Pacific and Indonesian oceanic margins. The warm and broad Tethys Ocean separates the Indian plate in the south from the Eurasian plate in the north, while the former subducts beneath the latter. In the meanwhile, the Pacific plate continuously subducts westward beneath the Eurasian plate. As the rate of subduction decreases with the time, back-arc extensional basins began to form due to trench rollback along the subduction zone. Though it is still under debate on the timing of initiation of collision between India and Eurasia, the main stage or significant collision probably took place between 55 and 45Ma. The collision and subsequent penetration of India into Eurasia cause retreat of the Tethys Ocean, crustal thickening of the southern and central Tibet, uplifting of Proto-Tibetan plateau, and southeastward extrusion of crustal material of Tibetan plateau. The timing and direction of extrusion of Tibet's crustal material coincide with acceleration of trench rollback of back-arc extensional system along the western Pacific and Indonesian oceanic margins. The collision caused shortening and trench rollback induced extension appear to form a causal "source-sink relationship". In the period of 30 to 20Ma, the northeastward convergence of the Tibetan plateau increased as the southeastward extrusion slowed down that in turn caused northeastward and eastward growth of the plateau. The Main Boundary Thrust became southern collisional boundary between the Indian and Eurasian plates. The northern deformational boundary migrated to the Kunlun Fault zone, forming compressional foreland basins such as the Qaidam, Hexi Corridor, and Longxi Basins. The rapid trench rollback has decreased along the subduction and back-arc extensional system along the western Pacific and Indonesian oceanic margins. As a result, the Japan Sea has ceased extension and the North China Plain Basin has changed from rifting to thermal subsidence. The east-west direction extension initiates in the interior of Tibetan plateau since approximate 10Ma ago, forming a series of north-trending grabens and half-grabens in the high altitudes above 5 000m. In the same time, the Tibetan plateau grows outward so that the Qilian Shan uplifted to form a major mountain range along the northern boundary and the Longmen Shan uplifted again to form an about 4000 relief with respect to Sichuan Basin. Along the eastern coast of Eastern Asia, subduction of Pacific plate beneath the Eurasian plate has accelerated to terminate back-arc extension.

Tectonic geomorphology introduces the quantitative topographic factors to describe and characterize the landform in real world, which is accepted as one efficient approach in neotectonics study now. More and more qualitative and quantitative researches have been implemented to delve into the response of surface topography to tectonic activity, or discuss the further subsequent geomorphology evolution. The various topographic characteristics along the middle-east segment of the Haiyuan Fault, which is located on the northeastern margin of Tibet plateau, indicate the different geotectonic backgrounds and evolution processes. Five quantitative topographic factors (i.e. elevation, slope, local relief, residual relief and channel steepness)derived from 90-m-grid SRTM DEMs all demonstrate higher values on the western section, lower values on the eastern section and middle section as well. However, all factors slightly increase to local peak values at the southeastern tailing end. Combining with average annual precipitation and geologic mapping, we discuss the basic mechanism about how geotectonic, climate and bedrock type would impose and build up various landforms. As demonstrated by our analysis our analysis, the precipitation is thought to aggravate the surface erosion and accelerate the landform evolution, and there is no significant correlation between the distribution of topographic factors and the bedrock type. Statistic result indicates the relative strong extrusion uplift on the western section. The middle part is a transitional zone and affected by Yellow River incision and widespread fluvial terraces. The influence of compressive folding at the southeastern tail of large strike-slip fault is also revealed by topographic variations.

The reconstruction of Green function by cross-correlating long time ambient noise has been extensively used by seismology community and found its applications in many fields such as structural inversion and stress-related velocity monitoring. Analysis on the ambient noise energy, especially its azimuthal distribution and seasonal variation is now becoming more and more important to obtain reliable and precise information from noise cross-correlation function(NCF). In this paper, more than four years vertical records of 33 broadband stations in Ningxia and its adjacent region are cross correlated and stacked monthly to obtain the distribution and variation of noise energy for both 5～10s and 10～20s periods range using normalized background energy flux method. Seasonal variations of strength for both ranges are observed and agree well with the ocean wave activity, which are strong in winter in the northern hemisphere and relatively weak in summer for same hemisphere. But the azimuthal variation are different. For 5～10s noise, the energy mainly comes from the costal line of southeast China. For 10～20s noise the azimuth of the dominant energy has strong seasonal variation. Back projections of the corresponding dominant noise energy azimuth range indicate that the noise field in Ningxia is controlled by several oceans simultaneously but certain ocean may take the main control on the overall noise energy distribution. Due to the none-uniform and none-random properties of noise filed there, we suggest that evaluation of noise field characters should be made before further studies are conducted, especially for time lapse based investigation.

A possible three-dimensionally highly-curved fault,suspected as the ruptured structure of the Lushan M7.0 earthquake,is revealed by relocated aftershocks. A recent study shows that obvious differences exist between curved fault and straight fault under the ground in regard to dislocation patterns and co-seismic stress responses on the planes ruptured during an earthquake. Infinite half-space dislocation models reveal that the characters of surface displacements due to a curved fault are similar to that from straight reverse fault as a whole. Nevertheless,the horizontal displacements due to slip on a curved fault show closer trend parallel to the direction of regional shortening and higher magnitude than that from a straight fault. Subsequently,the curved fault is suggested to be more capable of transferring horizontal movement of hanging-wall materials in large area. Relative to the case on a straight fault,horizontal displacement in foot-wall area of a curved fault decays more with distance from source fault. On the other hand,the curved fault generates obviously less co-seismic uplift while larger and more extensive surface drop somewhere than the reverse fault or left-lateral reverse fault of the same size but with straight fault planes does. For relatively small magnitude of main shock,it is not easy to determine whether the structure of rupture during Lushan earthquake is highly-curved fault or not due to the sparse observations on co-seismic deformation like GPS.Dense and high-resolution observations should be required to survey the features of focal structure in detail.

As the outermost fault zone in the northeastern margin of the Tibetan plateau,the deep structures,distribution,movement feature and deformational mechanism of the Niushoushan-Luoshan Fault zone are crucial to understand the formation and evolution of the arcuate fault zones in the northeast corner of the Tibetan plateau. In this paper,we analyze four seismic reflection sections across the Niushoushan-Luoshan Fault zone and map in detail the area within the fault zone. These data indicate that the Niushoushan-Luoshan Fault zone is a discrete fault zone. The fault zone can be subdivided into three parts: the south part,i.e.the Luoshan Fault,is characterized by positive flower structure,shown as remarkable right lateral strike-slip; in the middle segment,that is,the Niushoushan Fault,no active fault exists on the east flank of the Niushoushan,and this region is dominated by intensive folding; the north part,the Sanguankou Fault,is a left-lateral strike-slip fault. The discontinuity and segmentation feature of the Niushoushan-Luoshan Fault zone suggest different deformational styles in different locations of the fault zone associated with the process of northeastward propagation of the Tibetan plateau.

K-Feldspar MDD(Multiple Diffusion Domain)and fission track are two commonly-used methods in low closure temperature thermal chronometry.By modeling both the feldspar ³⁹ Ar/⁴⁰ Ar data and the fission track age and track-length data,the thermal history that sample underwent can be revealed and the effective temperature range of both feldspar ³⁹ Ar/⁴⁰ Ar method and fission track method is extended.Because of the multiple resolution of modeling,it is important to restrict the modeling process to gain a reasonable result,though it seems difficult.The possible problem in modeling thermal history is presented in this paper,and the helpful method that can be used to improve the result is illustrated by the sample collected along Saishitengshan in the northern margin of Qaidam Basin.Three rapid cooling events,occurring at 130～150Ma,30～40Ma and 5～10Ma respectively,in northern margin of Qaidam Basin are revealed by feldspar MDD method and fission track method.

Based on the field work and seismic reflection profiling data,the paper investigates the deformation characteristics of the Longquanshan Fault zone.The main thrust fault of the Longquanshan Fault belt lies in the west of the Longquanshan anticline and has different properties from northeast to southwest.In the north segment and south segment of the Longquanshan Fault,the plane of fault dips to northwest and is uncontinuous,but in the middle segment,the plane of fault dips to southeast and is continuous.Therefore,the middle part of the fault is the main segment of the Longquanshan Fault.Structural geometries of the middle segment of the fault suggest classical fault-propagation folding and the fault ruptured along different axial directions.Historical earthquakes and geomorphological response to activity of the Longquanshan Fault indicate that the fault was active from the early Pleistocene to late Pleistocene,and its activity is weak since the late Pleistocene,and gradually decreases from south to north.

Xiongpo anticline locates in Chengdu Basin,to the southeast of Longmenshan tectonic zone.It is an important deformation area where the Longmenshan thrust-nappe structure intrudes into the Chengdu Basin.The Pujiang-Xinjin Fault is an associated fault to Xiongpo anticline.The deformation mode between the fault and anticline fold is in concordance obviously.The geologic section across the anticline indicates that the south segment of Xiongpo anticline is an asymmetric fold and the northeast segment is symmetric,wide and gentle relatively.The fold includes Mesozoic and pre-Mesozoic strata.The topographical investigation reveals that the faulting is always associated with folding.At the northeast part of fold,the fold axial direction is parallel to the fault strike.Near the fault,the strata dips are remarkably different and the height difference of topography is large.The investigation of the Pujiang-Xinjin Fault did not reveal any obvious fault profiles and new activity characteristics.The Pujiang-Xinjin Fault has no influence on the gullies and T1 terraces widely developed in this area,but it controls the pluvial terrace which corresponds to T4 terrace of Nanhe river(the first-order branch of Minjiang River).The OSL age of the pluvial terrace is older than 130ka.All above indicates that the activity age of the Pujiang-Xinjin Fault is at the early-Quaternary.By the late-Quaternary,the faulting weakened or was nearly inactive.So in the area,the major tectonic character is faulting associated with fold deformation,which is also the major deformation mode of Xiongpo anticline.

On 12 May 2008,a magnitude 8.0 earthquake occurred beneath the steep eastern margin of Tibetan plateau in Sichuan,China.Rupture occurred over a length of～240km along the central Longmenshan Fault(Beichuan-Yinxiu Fault)and ～72km along the Longmenshan piedmont fault(Guanxian-Jiangyou Fault).In order to know clearly the activity of the middle segment of Longmenshan Fault,we surveyed the earthquake rupture and excavated 5 trenches in the north part of the central Longmenshan Fault.Four of the five trenches have revealed the deformation of the Wenchuan earthquake and the characteristics of strong earthquake activity on this segment.The 4 trenches are briefly described as follows.The Fenghuang village trench locates on T₂ terrace or T₃ terrace of Pingtong River.The trench logs show that there is another earthquake event except the Wenchuan earthquake.As a tectonic deformation character,the thrust fault is exposed on the surface,the underground soils were thrust over the cultivated surface soil,forming thrust nappe and extrusion wedge.The bedrock near the fault has been compressed and fractured seriously,which is represented by overlap of some old scarps with new ones on the ground surface.The trench on T₁ terrace at Pingtong Panxuanlu records the zigzag deflections of marker bed.According to the recovery of marker bed,it is possible that there was an earlier earthquake event whose magnitude is equivalent to the present Wenchuan earthquake,because the footwall is higher than the hanging wall after the marker bed flattened,and the Wenchuan earthquake scarp on flood plain and T1 terrace is much lower than the scarp at the trench site.The scarp with a length of～20m and height of～2.7m is revealed by the trench excavated near the Da′ai School,but we can't see obvious signs of fault and faulting.Perhaps the fault displacement is represented by slightly folding of each deposit layer,which is one of the surface deformation models of thrust faulting.On T₁ terrace at Miaoziwan village,Nanba town,the trench displays that the vertical displacement of arc-deflection on marker bed is equal to the earthquake scarp height,indicating that this phenomenon is caused by the present earthquake event alone.Now,there are no results of dating samples,so we obtained the topographical age by comparing the adjacent surfaces.According to the dating results of terrace,the forming time of T₁ terrace is about 3000～5000a and T₂ terrace about 12000～20000a.It is revealed that the recurrence interval of strong earthquake on the northern segment of central Longmenshan Fault is more than 3000a.

Field investigation on the surface ruptures of the M_S8.0 Wenchuan earthquake along the segment between Beichuan and Qingchuan shows that there is one surface rupture zone developed on this segment,which extends generally along the Beichuan-Qingchuan Fault zone.Observation at Huangjiaba Chenjiaba,Guixi,Pingtong,Nanba,and Shikan suggests that the surface ruptures on this segment spread continuously along the trend of the fault,with single structure and a length of 60～90km.The surface rupture has not reached Guanzhuang of Qingchuan county.The observable rupture zone is about 62km,between Beichuan and Shikan,trending 20°～55° in general,dipping NW with an angle of 70°,showing mainly thrusting with dextral strike-slipping.The most distinct feature of the surface ruptures of this earthquake is the vertical surface bending,which indicates the thrusting of the deep fault.Its horizontal motion on this segment displays as dextral strike slipping,without sinistral slipping component.The value of the vertical coseismic displacements decreases gradually from 3m at Huangjiaba to about 1.5m at Nanba and Shikan;The amount of the dextral displacements does not change evidently,generally between 1.5m and 2.0m.Features of the surface rupture show that the causative tectonics of this M_S8.0 Wenchuan earthquake is the Yingxiu-Beichuan-Qingchuan Fault,whose movement is characterized mainly by thrusting,with a dextral slipping component,and the thrusting direction is from west to east.