The geological structure and sliding mode of the slopes in the Yigong landslide source area, Tibet
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摘要:
西藏易贡滑坡源区BH01、BH02与BH03斜坡体呈不稳定状, 严重威胁下游工程设施安全。为防控源区坡体再次高位滑动致灾, 亟待开展斜坡赋存的地质结构及变形趋势分析。文章基于2 m精度的Pleiades数字高程模型及地形影像, 厘定了定量地貌学、地质构造与滑坡学3方面证据, 确定易贡滑坡源区具有前缘叠瓦式逆冲断裂区单面山、逆冲断裂区块体、走滑断裂区块体、走滑断裂区北东向拉裂槽4个次级斜坡单元。现场地质调查发现源区坡体内发育倾向南东、南西两组主控结构面, 这两组结构面是滑坡前缘逆冲断裂、后缘走滑断裂渐进活动的结果。与山脊近直交的北东向拉裂槽可能与晚期东西伸展变形背景相关。研究认为在地质构造影响下, 易贡源区斜坡沿着北东向拉裂槽下延结构面呈现多级、多期次深层滑移, 具有岩质滑坡蠕滑-拉裂-剪断型滑动机制。依据源区拉裂缝扩展的深度判断, 源区BH02坡体具有潜在加速滑移风险, 且BH03坡体亦不稳定。
Abstract:The unstable slopes of BH01, BH02, and BH03 in the Yigong landslide source area in Tibet threaten the safety of major engineering facilities downstream. In order to prevent and control the disaster risk caused by the high-elevation sliding of blocks, it is urgent to analyze the geological structure of the slope in the above-mentioned source area and their deformation trends. Based on the Pleiades digital elevation model with a precision of 2 m and its topographical shadow, this paper draws up evidence from three aspects: quantitative geomorphology, geological structure, and landslide science. In addition, it is preliminarily determined that the source area of the Yigong landslide has four secondary slope units, including the cuesta in the front imbricated thrust-fault zone, the block in the thrust-fault zone, the block in the strike-slip fault zone, and the NE-trending rift zone. There are two primary control structural planes in the slope, dipping southeast and southwest, respectively. The geological survey of the line has confirmed that the above two groups of structural planes are related to thrust faults and strike-slip faults in the imbricated nappe. The NE-trending rift crosscutting the ridge may be related to the recent EW-extensional deformation of the nappe. With the above-mentioned geological structures, the slopes in the Yigong landslide source area show multi-stage and multi-phase deep sliding along the NE-trending rift zone and have the creep-tension-shear sliding mechanism with rock landslide. According to the extension depth of the tensile fractures in the source area, the BH02 block has the potential risk of accelerated slippage. Moreover, the BH03 block is also unstable.
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Key words:
- geological disaster /
- Yigong landslide /
- source area /
- imbricated nappe structure /
- fault /
- sliding mode
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图 1 西藏林芝易贡滑坡构造背景与关键块体位置
a—研究区断裂与地震活动背景；b—区域地质背景；c—易贡滑坡源区强变形坡体分布(镜向NE)
Figure 1. The tectonic geological background and key block location of the Yigong landslide in Nyingchi city, Tibet
(a) The background of fault and seismicity in the study area; (b) The regional geological background; (c) The distribution of strongly deformed slopes in the source area (towards NE)
图 2 易贡滑坡及相邻沟谷地质地貌特征
a—滑坡源区及临区地貌；b—甲中村至后山地质剖面；c—通加村至后山地质剖面；d—易贡扎木弄沟地质剖面
Figure 2. The geologic and geomorphic characteristics of the Yigong landslide and adjacent valleys
(a) The geomorphic characteristics in the source and adjacent areas; (b)The geological section from Jiazhong village to the top of the slope; (c)The geological section from Tongjia village to the top of the slope; (d)The geological section of the Zhamunong gully at Yigong village
图 3 易贡滑坡源区地形及其次级地貌单元
a—源区斜坡单元划分(镜向NE)；b—源于2 m精度地形数据的地貌形态；c—斜坡后缘地形；d—斜坡后缘拉裂槽(镜向SE)
Figure 3. The topography of the Yigong landslide source area and its secondary geomorphic units
(a)The slope zoning in the source area(towards NE); (b)The geomorphology derived from the 2 m precision topographic data; (c) The geomorphic morphology at the upper edge; (d)The crown cracks at the upper edge(towards SE)
图 4 易贡滑坡源区主控结构面展布特征
a—易贡滑坡源区2m精度地形及内部结构面展布；b—倾向SE、走向NE结构面投影；c—倾向W、走向SN结构面投影
Figure 4. The distribution characteristics of the main controlling structural planes in the Yigong landslide source area
(a)The topography and the internal structural plane distribution derived from the 2 m precision data; (b) The projection of a SE-dipping and NE-striking structural plane; (c) The projection of a W-dipping and SN-striking structural plane
图 5 易贡滑坡源区断裂带露头及其地质剖面
a—源区逆冲断裂露头(镜向SE)；b—逆冲断裂带地质剖面；c—逆冲断裂及碎裂岩(镜向NE)；d—沟谷走滑断裂带左侧露头(镜向NE)；e—沟谷走滑断裂带右侧露头(镜向NE); f—源区走滑断裂地质剖面
Figure 5. The outcrop of the fault zone and its geological profile in the Yigong landslide source area
(a)The outcrop of the thrust fault in the source area(towards SE); (b)The geological profile of the thrust-fault zone; (c)The cataclastic rock and the thrust fault(towards NE); (d)The left outcrop of the strike-slip fault zone(towards NE); (e)The right outcrop of the strike-slip fault zone(towards NE); (f)The geological profile of the strike-slip fault in the source area
图 6 易贡滑坡源区叠瓦式推覆构造
a—易贡滑坡源区地质构造(镜向NE)；b—叠瓦式构造模式(Abd El-Wahed et al., 2016)
Figure 6. The imbricated nappe structures in the Yigong landslide source area
(a) The geological structure in the source area(towards NE); (b) The imbricated structural model (Abd El-Wahed et al., 2016)
图 7 易贡滑坡2000年源区滑面形态
a—易贡滑坡楔形体双滑面形态(镜向NE)；b—易贡滑坡主滑面形态(镜向E)
Figure 7. The slip surface morphology in the Yigong landslide source area in 2000
(a) Double-slip surface of the Yigong landslide(towards NE); (b) The main slip surface of the Yigong landslide(towards E)
图 8 易贡源区走滑断裂带及内部碎裂岩结构
a—易贡源区走滑断裂带(镜向NE)；b—易贡源区走滑断裂带内碎裂岩结构(镜向NE)
Figure 8. The strike-slip fault zone and its internal cataclastic rocks in the Yigong landslide source area
(a) The strike-slip fault zone (towards NE); (b)The cataclastic rocks in the strike-slip fault zone (towards NE)
图 9 易贡滑坡源区关键块体及其拉裂缝展布形态
a—蠕滑-拉裂-剪断型锁固岩质滑坡早期识别模式(唐鹏，2021)；b—易贡滑坡源区斜坡变形体分布(镜向NE)
Figure 9. The key blocks in the Yigong landslide source area and the distribution pattern of their tensile cracks
(a)The failure mode of the creep-tension-shear mechanism; (b)The distribution of the deformed slopes in the source area(towards NE)
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