GEOMORPHIC EXPRESSIONS OF QUATERNARY TECTONIC STRESS FIELD IN THE SOUTHERN SECTION OF THE EASTERN PIEDMONT FAULT ZONE OF TAIHANGSHAN MOUNTAIN
Han Mu-kang Zhu Shi-long (Dept. of Geography, Peking University) Zhao Jing-zhen Zhan Xian-rong (Seismological Bureau of Henan Province)
The southern section of the NNE-trending Eastern Piedmont Fault Zone of Taihang-shan Mountain is represented by the Tangyin graben which demonstrates itself as a semig-raben in its northern segment and as a graben properly in the southern segment, and was formed in Tertiary time, filled mainly with lacustrine and fluvial-lacustrine deposits of the same age. This graben experienced right-lateral compressional and uplifting movements under the action of the NE-SW principle compressional stress since the Quaternary time that pro-duced the following effects: the Tertiary vast ancient lake which was formed by the right-lateral tensional downfault under the action of principal compressional stress of the above mentioned direction during the Tertiary time disappeared; the Pliocene lacustrine and flu-vial-lacustrine deposits in the piedmont zone west of the Tangyin graben uplifted as a high terrace and those east of the Tangyin graben upheaved as a long upwarp paralleling the gra-ben; and two pairs of NW-trending en echelon drag upwarps and downwarps formed on the narrow long block within the graben. The upwarps consist of the Pliocene lacustrine and fluvial-lacustrine deposits, and the downwarps are filled with the Quaternary alluvium. Such distinct features of the Quaternary tectonic stress field in the area studied are in-dicated by landforms, by distribution of the Tertiary and Quaternary strata and the traces of recent faulting in them, by changes of drainage density and channel slope within the Tang-yin graben. They are also revealed by interpretation of lineaments on the satellite images and its statistic analysis, repeated levelling and focal mechanism solution. The integrate application of various methods with preclusion of non-tectonic effects and the comparison of their results are emphasized. During the statistic study of fractures and faults displayed in the form of lineaments on satellite images and in the form of valley tre-nds on topographic maps, a choice of the Tertiary-Quaternary active faults and identifica-tion of their nature and sense of motion are stressed.