Active Features Study In Late Quaternary Of The Northern Piedmont Fault Of The Changlingshan

The northern piedmont fault of the Changlingshan is belong to Gulang-Zhongwei-Tongxin active fault zoon of the north Qilianshan fault system, which is attributed to strong earthquake active zoon of the northeastern margins of Qinghai-Tibetan Plateau. The epicentral distance from the south of Zhongwei Ms=7(1/2) earthquake (epicenter: N37.5°, E102.7°) to the active fault east port (Baidunzi) and from Gulang Ms=8.0 earthquake (epicenter: N37.4°, E105.3°) to the active fault west port (Huazhuang) is respectively approximate 120Km. In addition, the Zhongwei active fault has paid more attention to study because it is decided to water and electricity dam-site in Heishan gorge of the Huanghe River. And Gulang active fault zone (especially midwest segment was named Tianqiaogou-Huangyangchuan active fault) has worked over far and wide as it is near the epicenters of the Gulang magnitude 8.0 earthquake. However, the northern piedmont fault of the Changlingshan, a joint between the above active faults, is a weakness tache of active fault research in the same area.The northern piedmont fault of the Changlingshan was formed around the early of Galedonoid structure period and went through more than one time tectonic movement in long-term crustal deformation, and be more strengthened since the Himalayan movement periods. This fault is not only formed a first boundary of the different physiognomy units, but also is it a boundary of the different neotectonic domains, as well as the different active crustal blocks. There is a different tectonic environment and sediment construct beside the fault. Further more, the active fault shows that it is a thrust fault itself in the earlier and horizontal sinistral-lateral strike-slip and dip-slip motion in the later stage. The different development stage the active fault experienced is related with the changes of area stress field direction.According to the field investigation, the northern piedmont fault of the Changlingshan is about 58Km-long from the south of Baidunzi of Jingtai country to the westward Huazhuang south, Dajing town. It is shown itself a compressed decumbent "S" in reverse style and striking nearly EW. The interspace of the fault shows that it is protruded obviously to northward. This fault is a left-slip and dip-slip movement and also is a clearly strongly active fault zone since the late quaternary. The active fault is characterized by left-lateral shear strike-slip movement. Therefore, in this paper the features indicated that it is a strongly stick-slipped mode by the macroscopically and microscopically (fault gouge) research.Linking to field investigation, the horizontal sinistral displacements of the active fault gradually increase from east to west. But the vertical displacements have formed from the Holocene period are in the contrast. It is a mutual compensation model between the horizontal and vertical displacement. Using displacements and corresponding ages the paper gets the active fault slip velocity include the horizontality and verticality. The average horizontal...