Activity Study On Xinjiang Fukang Fault Zone Since The Late Quaternary

Fukang fault zone is the boundary line of Bogeda Mountain and Zhungaer basin. It is located at the front of thrust faulting zone whose thrust direction is south to north. Fukang fault belongs to the western part of the Bogeda piedmont fault zone. It is meaningful to carry out the studies regarding deformation features, activity intensity and activity history since the Late Quaternary on this fault zone systematically. Based on the previous researches, in this paper, we carried out detailed field investigation, measurement on the deformation zone, large-scale trenches evacuation, and so on. It is to discuss a part of the problems about the fault geometry, kinematics and study the paleoearthquake further. It is our aim to provide a reliable basis for analyzing the deformation of Bogda arched nappe structure.Fukang fault zone is consisted of three segments that are Gumudi, Shuimohe, and Sigonghe fault zone. The long-term thrust faulting affects the landform evolution and deposition seriously, and it is characterized by differences in topography that is hills in the south and basin or plain in the north. River geomorphology and piedmont alluvial fans are sensitive to the tectonic activity, alluvial fans along the fault were beaded-style development, and the image features significantly; the different-time alluvial fans in the mountain rivers were embedded-style widespread development. The deformations of river terraces were recorded since the late Quaternary.Through field investigation and trench excavation we have a better understanding on the fault geometry and kinematics. Fukang fault is characterized by low-angle thrusting from south to north with20°. Fracture deformation style is complex under the environment of local tensile stress, leading to that normal faults develop combined with thrust faulting, and existing expansion forward and backward with "overlap" or "stack" style. The thrust faulting cuts folds that develops in the south of fault zone. Data shows that the fault extends down with "plow" style and lower angle, and that it is convergent with Yamalike fault zone and Erdaogou fault zone.Paleoearthquake studies show that six paleoseismic events have happened since the late Pleistocene in the fault zone. The first one can not determine the specific time. The remaining five were in chronological order:before (21.60±1.83)Ka.BP,(15.02±1.27)Ka.BP,(11.03±0.84～13.59±1.16)Ka.BP, not long before (8.32±0.67)Ka.BP, and (4.91±0.42々5.27±0.45) Ka.BP. The events interval is2.0-6.5Ka. The max earthquake oblique dislocation was3.1m, and estimated magnitude is about7.3. By comparing the intervals and the elapsed time, it is indicated that the seismic risk of Gumudi fault zone is strong, while Sigonghe fault is not significant.