There were several strong earthquakes of M_S≥7.0 occurring in the eastern Tianshan in the history, which is an important part of Tianshan earthquake zone. The Tangbal-Tasdun Fault is a left-lateral strike-slip fault zone of Late Pleistocene in the northwest of Barkol Basin. The study of the characteristics of its late Quaternary activities is one of the important basic work to understand the risk of strong earthquakes in Barkol area. Due to the low level of research in the eastern Tianshan region, there is a lot of controversy over the historical earthquakes. But there is no doubt that this area has the ability of generating earthquakes of magnitude greater than 7.0. Current GPS monitoring data on both sides and inside of Tianshan Mountains shows an about 20mm/a northward movement of the Pamir and Tarim plates, but a 4mm/a crustal movement rate of eastern Tianshan. This indicates that the tectonic activity of the western section of Tianshan Mountains is obviously stronger than that of the eastern section. However, according to the historical earthquake records of eastern Tianshan, there are at least two earthquakes of magnitude 7 or above happening in Barkol region. This indicates that the tectonic activity in the Barcol area is intense and the area has the condition for generating strong earthquakes.
In this paper, the methods of high resolution satellite image interpretation, field observation and analysis, micro-geographic survey and trenching are used. The geometric distribution characteristics of the Tangbal-Tasdun Fault are determined, which reveals the movement and activity of the fault zone. The activity parameters of the fault since late Pleistocene are preliminarily obtained. The results show that the fault is left-handed strike-slip with thrust motion. A surface rupture zone with a length of about 50km is developed in the east of Jijitaizi Village. The fault offset the T2 terrace with a vertical displacement of about 0.9m and a horizontal displacement between 9m and 11m. The vertical displacement of T3 terrace is about 1.6m, and the horizontal displacement is between 13m and 20m. To the west of Hongjingzi Town and Tashbastawu Village, the fault is distributed in a straight line on satellite images. The fault offset the latest geomorphic surface, with the minimum vertical displacement of about 0.1m, the maximum vertical displacement of 2m, and the horizontal displacement of 1.8~4.3m. The horizontal displacement of the fault is larger than the vertical displacement of the same period. The excavation of a trench near Kutaizi village shows that the fault has obvious characteristics of strike-slip movement. According to the phenomena of water spraying and sand emitting along the fault and the relation of cut and cover between the fault and strata, two ancient seismic events are revealed in the trench. The most recent event ruptured the ground surface. According to the empirical formula for magnitude estimation, M=7.13+0.68lgD, it is calculated and inferred that this fault section is qualified for the occurrence of M7.3~7.4 earthquake.

Paleoearthquake study is a basic research that can be favorable for the understanding of deformation pattern, intensity and time scale of the fault structure. The Yanqi Basin is an intermountain basin located in the eastern part of southern Tianshan Mountains. The present-day tectonic stress field of the basin is dominated by compression with strike-slip component. Both the north and the south marginal faults are Holocene active faults. The Kaiduhe Fault on the southern margin is a strike-slip fault. The Hejing Fault on the northern margin is a neogenic thrust-fold belt dominated by thrust faulting and extending towards the basin. The Hejing thrust fault has the potential to generate M7 earthquake in the future. Therefore, it is important to study the rupture model and time series of paleoearthquakes of the Hejing thrust fault-fold belt. According to the surveys, the major thrust fault at the south limb of the Haermodun anticline thrusts inwards the basin, with a dip angle of 30°, producing three paleoseismic scarps in T₁ terrace and washland. We determine the time series of six paleoseismic events by the cut-cover relationship of marker stratums in five trenches, date the age of stratums and colluvial wedges by ¹⁴C and OSL dating method, and obtain the recurrence intervals of the paleoseismic events using progressive constraining method. The rupture models of the Hejing fault are summarized. The fault F₁ ruptured in every paleo seismic event, but fault F₂ only ruptured in event E, F₃ only ruptured in event D and E. In other words, Event D ruptured the three faults simultaneously, Event E ruptured two faults, and the other events only ruptured fault F₁. There exist both certainty and uncertainty in the rupturing of Hejing thrust fault in the paleo-earthquakes.

The Yanqi Basin is an important depression area of the Tianshan Mountains near the northeast margin of the Tarim Basin. The Hejing thrust-fold belt,a renascent thrust-fold belt with intense tectonic activity,is located on the north margin of the Yanqi Basin. We calculated the shortening and uplifting of the Hejing thrust-fold belt since Quaternary to analyze the tectonic activities of this region,then,made a preliminary estimation of the shortening and uplifting rate in the Yanqi Basin and compared the result with other areas to demonstrate the role of the Yanqi Basin in the tectonic deformation of Tianshan in late Cenozoic. With few seismic data but abundant attitude of stratum and fault,we restituted the geometry of the fold to calculate the shortening and uplifting of the fold and slip of the fault on the Hejing thrust-fold belt which has a simple and intact structural pattern,and obtained the shortening amount of 1.79km,0.88km and 26m,respectively since early Pleistocene(1.8Ma),middle Pleistocene(780ka) and late Pleistocene(80ka). The respective shortening rate is estimated as 0.99mm/yr,1.13mm/yr and 0.33mm/yr. The intensity of tectonic activity is not constant on the Hejing thrust-fold belt since the beginning of deformation. Compared with the result of crustal deformation,Yanqi Basin,as a major depression on southeastern Tianshan Mountains,absorbs most of crustal shortening of this area(86°～88°E)and exhibits strong deformation of the newborn thrust-fold belt on the northern margin of the basin.

Reverse fault-anticline is an important structure form in Tianshan area.The study on the syntagmatic relation and formation mechanism between active faults and anticline in reverse fault-anticline will help understand the structure system under extrusion stress.Haermodun anticline is a neogenic thrust-anticline in the north margin of the Yanqi Basin.It is the product of reverse fault extending to the inside of the basin.The main reverse fault of the anticline thrusts inwards the basin,with a dip angle of 30°.The present-day tectonic movement is intense along the fault.By interpreting aerial photos of the Haermodun anticline,measuring the scarp profiles and excavating trenches across the fault,we find that three different types of faults have been developed on the different levels of river terraces crossing the anticline,namely,the main reverse fault in front of the anticline forelimb(southern limb),the back thrust fault on the forelimb and the bending-moment normal fault on the top of the anticline,respectively.The main reverse fault has produced three scarps on T₁ terrace,with heights of 4m,0.8m and 1.8m,respectively,and a high scarp on T₂ terrace with a height of 16m.The back thrust fault has produced 2-4 reverse scarps,with the height up to 4m The bending-moment normal fault has produced about 10 scarps on all levels of terraces except T₁ on the top of anticline,and the height of a single scarp can reach 14.5m.The older the terrace,the higher the total height of scarp.Analysis on the geneses of the three faults reveals that the main reverse fault controls the growth of the Haermodun anticline.The back thrust faults help the main reverse fault release the compressive stress,and the part between the main reverse fault and the back thrust fault is extruded.The bending-moment normal fault is produced in the top of anticline.The top of the anticline is a tensional stress area.Back thrust fault and main reverse fault are synchronous.But the scale of back thrust fault is several times smaller than the main reverse fault.Bending-moment normal faults are synchronous with fold deformation.Accompanying the beginning of fold deformation,the bending-moment normal faults began to expand and grow gradually downwards from the top of anticline,synchronously.