青海达日断裂中段构造活动与地貌发育的响应关系探讨

THE RELATIONSHIPS BETWEEN NEOTECTONIC ACTIVITY OF THE MIDDLE SEGMENT OF DARI FAULT AND ITS GEOMORPHOLOGICAL RESPONSE,QINGHAI PROVINCE,CHINA

青海达日地区发育了多条晚第四纪活动断裂带,以NW—NNW向和近SN向为主。通过航卫片解译和野外实地调查发现,达日断裂中段晚第四纪新活动性尤为显著,其性质以左旋走滑为主,至今部分地段仍保存了清晰的1947年达日7级地震地表破裂带,其破裂样式具有分段性和多样性,反映了局部构造应力的差异。达日地区作为典型的活动构造区,是研究新构造运动与地貌响应的理想场所。因此,文中采用ASTER GDEM V2数据提取了该地区的水系网络和亚流域盆地参数,计算了亚流域盆地面积-高程积分曲线和积分值(HI值),讨论了其构造活动性及地貌响应的关系。区内黄河的6个亚流域盆地的面积-高程积分曲线形态分析结果表明,这6个亚流域盆地均处于地貌演化阶段的"壮年期",其演化过程表现出很好的同步性,反映了区域性构造隆升或沉降作用的总体结果。而且,区内亚流域盆地的面积-高程积分值(HI值)分布特征表明,HI低值分布与第四纪断陷盆地和河谷盆地范围相一致,反映了局部不同构造沉降和侵蚀作用的结果;HI高值则主要出现在达日地震地表破裂带由NWW向NW转向的部位,以及早侏罗世与晚三叠世花岗闪长岩体分布的地方,也很好地反映了局部构造作用的变化和地层岩性的差异。

There are numerous Late Quaternary active faults in Dari area, Qinghai Province, with the major strike orientation of NW-NWW and SN. Through analyzing of satellite images and field investigation, we observed significant new activity of the middle segment of Dari Fault during Late Quaternary. The Dari Fault locates in the south of Qinghai Province, and it＇s a left-lateral strike-slip active fault. Along the studied segment, the surface rupture zones of the M 73/4 earthquake are still preserved. The rupture styles of the M 78/4 earthquake surface rupture zones are varied and diversified in different segments. This feature is represented by changes of local tectonic stress. The Dari area, as a typical active tectonic zone, is ideal for studying the neotectonics and the geomorphological responses. So in this paper, we also discussed the relationship between the tectonic activities and its geomorphological response in the study area. Analysis on ASTER GDEM V2 digital data enabled us to extract the sub- basins and rivers in this region, and finally determine the hypsometric curves and hypsometric integral （HI values） of the sub-basins. Hypsometry is adopted to analyze the evolution processes of six sub- basins of the Yellow River in the study area. The results show that the geomorphological evolution of the six sub-basins is in the stage of maturity, and the evolution process is highly synchronized, indicating the overall result of regional tectonic uplift or subsidence. Furthermore, the distribution characteristics of the hypsometric integrals （HI value） of the sub-basins reveal that the location of low HI value areas coinsides with the distribution of Quaternary graben basins and valleys, reflecting the results of different local tectonic subsidence and erosion. On the other hand, the high HI areas mainly occur where the strike of the Dari earthquake surface rupture zone changes from NWW to NW and where Early Jurassic and Late Triassic granodiorites are distributed, indicating clearly the variation of local tectonics and difference in lithology.