Abstract: The quantitative study of geomorphic features associated with active faults is important for revealing paleoseismic and fracture characteristics. Faulting associated morphology, namely fault scarp, is an important geomorphological response to fault activity; therefore, it is a good geomorphic mark for effectively identifying active faults. In recent years, the rapid development of UAV low-altitude remote sensing technology has enabled rapid acquisition of high-resolution geomorphic data. In this study, we used UAV low-altitude remote sensing for geomorphologic observation to collect high-resolution digital terrain data near the fault scarp at Zhangliugou Beach. The fault scarp is located on a Class II terrace, covering a rectangular area of 800 m×400 m for imaging acquisition. After a series of imaging processing, we finally acquired DEM (digital elevation model) data with a ground resolution of 0.1 m in the target area. Based on this DEM data, elevation and slope profiles orthogonal to the fault scarp can be extracted. Using the topographic information displayed in the elevation profiles, the height of the fault scarp was determined to be 2.81±0.05 m. The slope curve feature from the slope profiles inferred that the scarp experienced at least two fault-off activity events, and the fault scarp has an upward “bulge style”. Through trench interpretation, we also determined that at least two active events occurred at the lower fault scarp: the earlier seismic event was close to 3.68±0.14 ka B.P., and the 1927 magnitude 8 earthquake was the latest activity. The cumulative vertical displacement of the two fracturing activities was 2.80±0.2 m. Comparing the above two research methods, we found that the trench structure analysis yielded basically the same quantitative geomorphological information as that obtained from the low-altitude remote sensing technology, both could effectively reveal the paleoseismic period and cumulative co-seismic displacement. Finally, by considering both sedimentary/structural information of strata units in the trench and slope profile features, we proposed the “scarp bulge” geomorphological response pattern based on the fault-propagation folds model to explain the occurrence of the upward “bulge style” of scarp. Experimental results proved that technology using UAV low-altitude remote sensing for geomorphologic observation can quantitatively or semi-quantitatively reveal the activity information of the underlying fault of scarp. When it is combined with traditional fracture research methods, this technology can more fully explain depositional and structural features as well as topography and geomorphology of active faults. And it can be used, in general, as an auxiliary method in traditional paleoseismic research for its unique methodological advantages.

Key words: active faults, digital terrain data, the morphology of fault scarp, UAV low-altitude remote sensing