天山北麓库松木楔克断裂东段褶皱带晚第四纪地壳缩短及大地震风险

挤压造山带前缘的活动推覆构造是特大地震（≥8级）多发的场所，地表活动逆断层上盘常伴随活动褶皱出现。逆冲型地震的发震断层通常隐伏于地下或部分出露地表，地表断层滑动速率不能代表其深部的滑动速率，导致低估其发生大地震的震级和风险。以往的工作发现，隐伏活动逆断层的长度、倾角与上盘伴生的褶皱规模、形态有关，滑动速率为地表断层和褶皱的缩短速率之和。通过对库松木楔克断裂东段阶地和洪积扇堆积物形成年代测试和分析，结合实际测量断错地貌和褶皱弯曲洪积扇、阶地地形剖面，获得断裂东段晚第四纪的地壳缩短量，进而得到隐伏逆冲断层的滑动速率。建立研究区逆冲推覆构造的三维构造模型，获得逆冲推覆构造的几何参数，评估潜在地震的最大震级。选择合适的位置开挖古地震探槽，识别古地震事件，采集和测定地层年代样品，限定古地震年代，评价大地震的发震风险。结合大地测量、地质和地球物理资料，分析库松木楔克断裂在现今天山构造变形中的作用。

The active nappe structure at the front of the compressive orogenic belt is the site where many large earthquakes (M≥8) occurred in the world. On the upper plate of active reverse fault, some active folds are often accompanied. Seismogenic faults of thrust earthquakes are usually buried underground or partially exposed on the surface. Slip rate of surface reverse faults cannot represent the deep slip rate. For this reason, it often leads to an underestimation of the magnitude and risk of large earthquakes. Previous research shows that the length and dip angle of the hidden reverse fault are related to the scale and shape of folds associated with its upper plate. The slip rate of the hidden active reverse fault should be the sum of the shortening rates of the surface faults and folds..The distribution of active faults, active folds, flood fans, and terraces was determined through the tectonic geomorphic interpretation of satellite remote sensing data with high accuracy in the eastern segment of the Kusongmuxieke fault in the northern piedmonts of the Tianshan Mountains. Collecting and organising geological, seismic, and other geophysical data, we can establish a three-dimensional spatial structural model of thrust and nappe structures in the study area. On the alluvial fans and terraces with different ages, high-precision digital topographic maps are plotted with SfM at the typical locations of active fault structural geomorphology, and we can also obtain the faulty micro-topography and vertical displacement of active faults. Perpendicular to the fold axis direction, the topographical sections on flood fans or terraces surface were measured. Using the line-length balanced cross section, we can obtain the crustal shortening of folds recorded at different times since the late Quaternary. Some trenches with 2.5~3.0m depth are excavated at the location where the ground surface is weakly eroded on the alluvial fan across active fold area. No less than five cosmogenic nuclide samples were collected on each profile. The 10Be nuclide content is tested for each sample, and the age of landform exposure is fitted for each fans or terraces using mathematical method. Combining with regional climate change data, the landform ages are situated at the turning period from ice age to interglacial period. Based on the age of the geomorphic surface, displacement of the fault, and the amount of fold shortening, the crustal shortening rate in the eastern section of the Kusongmuxieke fault will be calculated. The geometric parameters and activity parameters of the thrust nappe are used to estimate the maximum magnitude of potential earthquake using statistical relations. Select appropriate fault geomorphic sites, we excavate paleoearthquake trenches with a depth of about 2.5m, identify paleoseismic events, collect and test serial dating samples, and limit paleoseismic events since the late Quaternary. Using the probability method, we can evaluate the risk of large earthquake. Based on geodetic surveys, active structures, and geophysical data, we will further study the role of Kusongmuxieke fault in today's mountain tectonic deformation.