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摘要
The Maqin-Maqu segment( MMS) of the East Kunlun fault zone(EKLF)is loeated in the seismic gap with a high seismic risk. Study on the geometric characteristics and late Quaternary differential tectonic activity of MMS is critical for carrying out the seismic risk assessment of the cities and towns with relatively high population like the Maqin and Maqu County in the eastern part of EKLF. Previous studies indicated that the late Quaternary left-lateral slip rate along MMS shows an eastward gradient decreasing. However, the geodynamic mechanism to explain this gradient decreasing of slip rate remains controversial. Therefore, accurately identifying the geometric and kinematic characteristics of the major fault zone of MMS and its branch faults can provide important clues for understanding the tectonic transformation mechanism and its seismic risk assessment along the eastern part of EKLF. The geomorphic index can quantitatively describe the geomorphologic characteristics, and effectively extract the active tectonic deformation from surface landscapes. The hypsometric integral index (HI) can well reveal the spatial distribution of the regional tectonic activity intensity by calculating the current three-dimensional volume residual rate of drainage basins. The stream-length gradient index (SL) csan effectively reflect the regional tectonic deformation by identifying the geomorphic anomalies of river longitudinal profiles. And the topographic relief ( TR) can directly evaluate the geomorphologic erosion in response to the regional tectonic activity. These geomorphic indices have been widely used to differentiate active tectonic deformation regionally. In this study, the geological and geomorphic interpretation of high-resolution remote sensing images are employed to determine the spatial distribution and geometrical features of the major fault zone and branch faults of MMS. The 30m AW3D30 data is used to extract systematically 69 drainage basins along the MMS and adjacent area by GIS spatial analysis technology. Our results indicate that the HI indices along the major fault zone of MMS are much higher in the western segment (0.77 ~ 0. 89)than in the eastern one(0. 15-0. 36), and its branch faults like the Awancang Fault(AWCF) and Gahai Fault( GHF)have similar variations. Along the major fault zone of MMS, the TR indices of the Maqin-Oulasuma fault intersection area reach about 400m, and the erosion amounts decrease eastward gradually (middle: 150-180m, east; 50~72m). The TR indices along AWCF also show a trend of decreasing from west( 280 ~ 350m) to east( 18~65m), and the eastern segment ( 25 ~ 100m) of GHF account for~10%~40% of the middle part( ~250m). In addition, the distributions of the Hack profile and SLK index vary spatially. In the western segments, rivers with up-convex Hack profiles and higher SLK abnormal values suggest that they are strongly affected by tectonic activity. Thus, the above-mentioned variations of geomorphic index values along MMS show a continuous eastward decreasing, which is displaying a similar trend as the late Quaternary long-term slip rate gradients along MMS. It demonstrates that quantitative geomorphologic analysis is of great indicative function on decoding geomorphologic responses to active deformation processes. Meanwhile, the spatial distribution of geomorphic index values and field geomorphologic investigations reveal that the major fault zone of MMS and its branch faults can be divided into 3 segments, and their activities also show an eastward decreasing. The HI and 77? indicate that the turning point of tectonic activity intensity of MMS is near the township of Oulasuma. Therefore, we infer that the slip rate gradient decreasing along MMS might be caused by tectonic transformation and strain distribution of the major fault of MMS together with AWCF and GHF, which are composing a typical horsetail-shaped fault system and play a key role on tectono-geomorphic growth in the eastern part of EKLF.
- 出版日期2022
- 单位中国科学院大学
