利用DEM技术自动提取龙门山南段青衣江阶地面的研究

河流阶地面是一种时间性、连续性非常高的层状地貌面,利用跨断层地区的河流阶地变形可以定量地判别一个地区的断层活动性。青衣江横跨龙门山断裂带南段是一条区域性大河,由于龙门山南段构造活动强烈且河流阶地被侵蚀程度严重,为了在室内更好、更快地解译青衣江河流阶地,使野外调查工作更具有针对性,本文在龙门山南段青衣江流域小关子至飞仙村一段,采用航测遥感技术制作的2m分辨率DEM和1/5万数字高程模型,基于Arc GIS和MATLAB平台进行了阶地面提取和聚类分析,以模拟野外测量阶地的流程,试图通过计算机提取,快速获取该地区更多的残余地貌面,建立起较为完整的河流阶地纵剖面。研究结果表明:野外测量数据与计算机自动提取结果相似度较高,具有较好的一致性;在完整的阶地剖面中发现了芦山盆地内部阶地具有疑似拱曲现象;在大川-双石断裂附近阶地有翘起现象,推测芦山盆地西缘阶地拱曲是由大川-双石断裂东侧的一条未知断层引起的,大川-双石断裂附近阶地的翘起现象可能是在断层逆冲推覆过程中形成的,同时结合区域年代历史数据,推测该地区(芦山盆地至大川-双石断裂)至少在晚更新世曾发生过构造活动。

An Automated Method to Extract Fluvial Terraces of Qingyi River on the Southern Longmenshan

River terrace is a kind of timeliness and continuous landforms and when crossing a fault they can be used effectively to identify the regional tectonic activity. Qingyi river is a regional river across the southern Longmenshan, because of the influence of fault activity and erosion, there retain a few of terraces. In order to identify fluvial terrace quickly and reduce the workload in the field, we utilized ArcGIS and MATLAB platform to extract terrace based on 2m DEM derived from aerial remote sensing technology and 1:50,000 digital elevation model, and then we carried out clustering analysis, field measuring simulation, Finally we obtained more local residual terraces through the computer quickly, and generated a more complete longitudinal profile of river terraces. Our field measurements confirmed high similarity and consistency with computer automatic extraction. In the complete terrace profile, we found a suspected arch phenomenon in Lushan basin and tilt of terrace around Dachuan-Shuangshi fault. We speculate thrust-nappe generate the tilt around Dachuan-shuangshi fault and an undiscovered fault on the east of Dachuan-shuangshi fault lead to the arch phenomenon in Lushan basin. Combining ages of terraces near this region, we infer this region has experienced tectonic activity since late Pleistocene.