APPLICATION OF SMALL UNMANNED AERIAL VEHICLE(sUAV)IN THE SELECTION OF SUITABLE SITES IN PALEO-SEISMIC STUDY OF BEDROCK FAULT SURFACES

doi:10.3969/j.issn.0253-4967.2023.04.002

Abstract

Abstract:

Bedrock normal fault scarps, as classical topographic features and geomorphological markers along mountain range fronts, form in consolidated bedrock due to faulting in extensional settings. They generally preserve more complete records of paleo-earthquakes than fault scarps in unconsolidated sediments. With the development of technologies such as fault surface morphology measurement and terrestrial cosmogenic nuclide dating, bedrock fault planes have become a nice object for paleo-earthquake study in bedrock areas. The reconstruction of paleo-seismic history from a bedrock fault scarp in terms of the times, co-seismic slips and ages by a combination of quantitative morphological analysis, TCNs dating and other physical/chemical index has been proven feasible by several previous studies.

However, this success heavily relies on a suitable site selection along the bedrock fault scarp because erosional processes can exhume the bedrock fault surface, and the sedimentary processes can bury the bedrock fault surface. Namely, non-tectonic factors such as gully erosion, sediment burial, and anthropogenic activity make bedrock fault planes difficult to record and preserve paleo-seismic information.

Therefore, to successfully extract paleo-seismic information from the bedrock area, it is necessary to select suitable study points along the bedrock fault scarp in advance. Traditional survey and mapping methods are time-consuming and labor-intensive, and it is difficult to understand bedrock fault scarps. The resolution of satellite images cannot obtain the fine structure of bedrock fault scarps. Small unmanned aerial vehicle(sUAV), combined with Structure-from-Motion(SfM)photogrammetry has emerged over the last decade. It is used as an established workflow in acquiring topographic data by filling the spatial gap between traditional ground-based surveys and satellite remote sensing images. As a low-altitude photogrammetry technology, it can quickly obtain high-precision three-dimensional surface structures of bedrock fault scarps.

In this paper, taking the Majiayao bedrock fault scarp at the northern foot of Liulengshan in Shanxi Rift as an example, the high-precision and three-dimensional topographic data of the bedrock fault was obtained by using sUAV combined with SfM photogrammetry technology. The high-resolution and high-precision images of tectonic landforms can be obtained conveniently and efficiently by sUAV survey. The sUAV-obtained photos can be further processed by the SfM photogrammetry for generating a digital 3D structure of the bedrock fault scarp with true or shaded color.

The non-tectonic factors such as rock collapse, sediment burial, and gully erosion along the bedrock fault scarp are identified by interpreting the 3D model of the bedrock fault scarp. The profile shape characteristics of the erosion, burial and tectonic fault scarps are summarized through fine geomorphological interpretation and fault profile analysis. For the erosion profile, the hanging wall slope is down-concave, showing that the fault surface below the ground surface has been partially exposed. For the bury profile, the hanging wall slope shows an obvious concave-up shape, indicating that the lower part of the bedrock fault surface has been partially buried by the colluvium. For the tectonic profile, the hanging wall slope shows a smooth and stable slope, showing the exhumation of bedrock fault scarp is controlled purely by tectonics. Finally, the study sites suitable for paleo-earthquake study on bedrock fault surfaces were selected, showing the important role of sUAV aerial survey technology in the selection of paleo-earthquake study sites in bedrock areas.

This study illustrates that based on the high-precision three-dimensional surface structure of the bedrock fault plane from sUAV aerial survey, the existence of non-tectonic factors such as gully erosion, sedimentary burial and bedrock collapse can be clearly identified. These non-tectonic sites can be excluded when selecting suitable sites for paleo-earthquake study indoors. The shape analysis of bedrock fault scarp is also helpful to determine whether the bedrock fault surface is modified by surface process and suitable for paleo-seismic study. The sUAV aerial survey can play an important role in paleoseismic research in the bedrock area, which can accurately select the study points suitable for further paleo-seismic work in the bedrock area.

Key words: small UAV aerial survey, site selection of paleoearthquake study, 3D model of bedrock fault scarp, fault profile shape, Liulengshan northern piedmont fault

摘要：

随着断层面形貌测量、宇宙成因核素测年等技术的发展, 基岩断层面成为在基岩区古地震研究的良好研究对象。但是, 受沟谷侵蚀、沉积覆盖和人为改造等非构造因素影响, 并非所有出露的基岩断层面都能完整记录和保存古地震信息。因此, 必须在基岩断层面上选择合适的研究点。传统的野外测量方法耗时费力, 难以掌握基岩断层面的整体信息, 即使通过高分辨率卫星影像也无法获得基岩断层面的精细结构。小型无人机航测(sUAV)采用低空摄影测量技术, 可快速获取基岩断层面高精度的地表三维结构, 为筛选目标工作点提供便利。文中以山西地堑系六棱山北麓断裂的马家窑基岩断坎为例, 采用小型无人机航测结合SfM摄影测量技术, 获得了基岩断层面的高精度三维地形数据, 通过精细地貌解译和断层坎剖面分析识别了沿断层坎分布的崩塌破坏、沉积埋藏和侵蚀剥露等非构造因素, 分析了侵蚀、埋藏和构造这3种典型的基岩断层面的形态特征, 选取了适合开展古地震研究的基岩断层面点, 展现了小型无人机在基岩区古地震研究工作中发挥的重要应用潜力。

关键词: 小型无人机航测, 古地震研究选点, 基岩断层面3D模型, 断层坎剖面形态, 六棱山北麓断裂

ZOU Jun-jie, HE Hong-lin, ZHOU Yong-sheng, WEI Zhan-yu, SHI Feng, GENG Shuang, SU Peng, SUN Wen. APPLICATION OF SMALL UNMANNED AERIAL VEHICLE(sUAV)IN THE SELECTION OF SUITABLE SITES IN PALEO-SEISMIC STUDY OF BEDROCK FAULT SURFACES[J]. SEISMOLOGY AND GEOLOGY, 2023, 45(4): 833-846.

邹俊杰, 何宏林, 周永胜, 魏占玉, 石峰, 耿爽, 苏鹏, 孙稳. 小型无人机(sUAV)在基岩区古地震研究选点中的应用[J]. 地震地质, 2023, 45(4): 833-846.

Figures/Tables 6

Fig. 1 Location of the study area(a), the distribution of aimed faults, and the location of the studied bedrock fault scarp(b).

Fig. 2 SUAV aerial survey(a), measurement of ground control point(b) and 3D model construction of bedrock fault scarp(c).

Fig. 3 The panoramic view and 3D topography of the Majiayao bedrock fault scarp on the Liulengshan northern piedmont fault.

Fig. 4 Three typical topography profiles of the bedrock fault scarps: erosional(a), buried(b)and tectonic(c).

Fig. 5 Schematic diagram of ways that may lead to exposure, burial, and deconstruction of bedrock fault scarps at the basin-range boundary(modified from Zou et al., 2022).

Fig. 6 The role of UAV aerial survey in the process of paleo-seismic research on the bedrock fault surface.

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