Abstract: The Huya Fault, located in the steep topographic boundary of the Minshan Mountains in the eastern margin of the Tibetan plateau, has documented many major earthquakes such as the 1630(M=6 3/4), 1973 Huanglong(M_S=6.5) and the 1976 Songpan-Pingwu earthquake swarm(M_S=7.2, 6.7, 7.2). While its activity remains unclear because of lacking Quaternary sediments. In the past few decades, there have been significant advances in understanding the relationship between bedrock channel landscapes and active tectonics, indicating that the bedrock fluvial features can well record the tectonic activity. Many studies reveal that tectonism is the primary factor of landscape evolution in tectonically active regions, and the erosional landscapes can be used to reveal tectonic signals on timescales of 10³~10⁶ years. The Huya Fault crosses the Fujiang drainage basin, making it suitable for the study of bedrock rivers and tectonic uplift in the eastern margin of Minshan. In this study, we calculate the geomorphologic indeices(hillslope, local relief, normalized steepness indices and hypsometric integral) on the basis of the digital elevation model(DEM) SRTM-1. For better understanding the tectonic activity along this fault, we derive some small catchments on the two sides of the Huya fault to analyze the differences of average steepness indices and hypsometric integral. Combining with field observations, lithology, precipitation and modern erosion rates, this study suggests that tectonic activity is the controlling factor of geomorphology in the eastern margin of the Minshan Mountains. We use focal mechanism solutions, GPS data and geomorphic evidence to explore the relationship between the geomorphologic indices of the Fujiang drainage and activity characteristics of the Huya fault. Our results suggest that:(1) The Fujiang drainage basin is in a steady state. The characteristics of the knickpoints indicate that they are mainly controlled by the locally resistant substrate. (2) The suggested value of the geomorphologic index on the west side of the Huya fault is generally larger than on the east side, showing differential tectonic uplift rates across the fault. (3) The difference of the geomorphologic index of the small catchments on both sides of the Huya fault is gradually increasing from north to south along this fault, in accordance with that the north and south segments of the Huya fault are dominated by strike-and reverse-slip, respectively.

Key words: geomorphologic indices, tectonic uplift, strike-slip fault, Huya fault, Fujiang drainage

摘要： 青藏高原东缘岷山东边界的虎牙断裂带强震频发，但因第四系保留有限，目前对于该断裂的活动性仍认识不清。而基岩山区河流地貌与活动构造关系研究发现，河流地貌特征能够很好地记录构造活动信息。虎牙断裂带横跨涪江流域，这为通过河流地貌研究虎牙断裂的活动特征提供了条件。文中选择涪江流域SRTM 30m精度数字高程模型（DEM）数据，利用GIS技术提取了涪江流域坡度（slope）、局部起伏度（local relief）、标准化陡峭指数（k_sn）、面积-高程积分值（HI）等地貌指数，并对跨虎牙断裂带小流域盆地的平均陡峭指数（k_s）和面积-高程积分值进行对比，结合野外调查、岩性、降水与现代侵蚀速率等特征，分析讨论了涪江流域地貌特征与虎牙断裂带活动特征的关系。研究表明：1）涪江流域基本处于稳态状况，区内仅有跨雪山断裂带的河道剖面显示明显的裂点，其余跨断裂河道剖面无明显裂点存在；2）虎牙断裂带两侧地貌指数差异明显，整体上表现为西高东低，这应与虎牙断裂的逆断活动有关；3）断裂两侧的小流域地貌指数差异分析表明，沿虎牙断裂带自北向南抬升作用逐渐增强，反映了虎牙断裂带北段以走滑为主，南段以逆断为主。该研究有助于提高对青藏高原东缘隆升变形机制的理解。

关键词: 地貌指数, 构造抬升, 走滑断裂, 虎牙断裂带, 涪江流域