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The formation mechanism of Suoertou landslide in Pingding-Huama fault zone, southern Gansu
Abstract
Pingding-Huama fault in southern Gansu Province is an active fault at present with characteristics of sinistral strike-slip. Suoertou landslide is a typical creep fracture zone landslide developed along Pingding-Huama fault zone. Field investigation and monitoring data reveal that Suoertou landslide is a giant landslide characterized by the development of many secondary landslides; landslide is composed of fault fracture zone, gravel soil and accumulated loess; the deformation of the landslide is intense; the landslide has many tension fractures and shear fractures lying in the creep deformation state. Suoertou landslide is formed under the coupling of endogenic and exogenic geological processes: the active fault controls the formation and development of the landslide, the rainfall is the main factor triggering the revival of the landslide. Therefore, the further study of the formation mechanism of Suoertou landslide can provide theoretical basis for the prediction and control of the creep fracture zone landslide.
... The composition of earthflow bodies comprises the main local weak rock lithologies (dominated by slates and phyllites) and a cover of loess and fractured rock. The basalslipsurfacedepth varies from 8 to 50 m ( Huang et al. 2013;Yang et al. 2013;Jiang et al. 2016). We analyzed the controls of movement of these earthflows by combining the characteristics of earthflows with displacements identified by the InSAR technique and the main lithology ( Table 2). ...
... The bedrock not only is characterized as shales, slates, and phyllites, but also contains sections where limestone is carried along by the landslide. The landslide has a length of 4.5 km, and widths range from 120 to 400 m with an area exceeding 3 km 2. It is estimated that the average thickness of the landslide is ~ 65 m with a volume of approximately 80 × 10 6 m 3 ( Huang et al. 2013). The current elevation difference from top to toe is approximately 900 m. ...
... The current elevation difference from top to toe is approximately 900 m. Monitoring data from ground-based instruments and InSAR techniques provide a record of displacement since 2000 ( Huang et al. 2013;Zhang et al. 2016). In addition, there is a rainfall station close to this earthflow, providing sufficient precipitation records to analyze the potential correlation with the time series displacements ( Fig. 7). ...
In the Zhouqu region (Gansu, China), landslide distribution and activity exploits geological weaknesses in the fault-controlled belt of low-grade metamorphic rocks of the Bailong valley and severely impacts lives and livelihoods in this region. Landslides reactivated by the Wenchuan 2008 earthquake and debris flows triggered by rainfall, such as the 2010 Zhouqu debris flow, have caused more than 1700 casualties and estimated economic losses of some US$0.4 billion. Earthflows presently cover some 79% of the total landslide area and have exerted a strong influence on landscape dynamics and evolution in this region. In this study, we use multi-temporal Advanced Land Observing Satellite and Phased Array type L-band Synthetic Aperture Radar (ALOS PALSAR) data and time series interferometric synthetic aperture radar to investigate slow-moving landslides in a mountainous region with steep topography for the period December 2007–August 2010 using the Small Baseline Subsets (SBAS) technique. This enabled the identification of 11 active earthflows, 19 active landslides with deformation rates exceeding 100 mm/year and 20 new instabilities added into the pre-existing landslide inventory map. The activity of these earthflows and landslides exhibits seasonal variations and accelerated deformation following the Wenchuan earthquake. Time series analysis of the Suoertou earthflow reveals that seasonal velocity changes are characterized by comparatively rapid acceleration and gradual deceleration with distinct kinematic zones with different mean velocities, although velocity changes appear to occur synchronously along the landslide body over seasonal timescales. The observations suggest that the post-seismic effects (acceleration period) on landslide deformation last some 6–7 months.
... The moving direction of Suoertou landslide is S135 E with an average slope of 12 . The thickness varies from 20 to 100 m with a volume of >8.8 Â 10 7 m 3(Huang et al., 2013b). The Suoertou landslide has been creeping at rates of 300-600 mm/year since 1970s(Jiang & Wen, 2014). ...
Landslides can be caused by natural forcing and anthropogenic activities. Zhouqu County (China) on the eastern margin of Qinghai‐Tibet Plateau is set within the active Pingding‐Huama fault zone with evident fractures on the land surface. Frequent landslides and debris flows have occurred in this region due to river erosion, rainfall and deforestation. Here we quantified the slope movements using time‐series synthetic aperture radar interferometry (InSAR) based on the ascending and descending Sentinel‐1 satellite images acquired between October 2014 and August 2020. We observed distinct displacements in the highly fractured fault zone. The eastward and vertical displacement time series between February 2017 and July 2020 were constrained by the common‐day ascending and descending acquisitions. The eastward rates (461 mm/year) were greater than those in the vertical direction (−185 mm/year). We also note displacement discontinuities across the thrust faults beneath the Suoertou and Zhongpai landslides. Seasonal variations in the displacement time series suggest that the cyclic rainfall is the primary driver for the mass wasting processes rather than the tectonic loading. As a complement to in situ observations, our results demonstrate that InSAR is an effective tool to characterize the spatio‐temporal nature of landslide displacements in complicated geological environments.
Plain Language Summary
Zhouqu County in the Pingding‐Huama fault zone in the eastern margin of Qinghai‐Tibet Plateau is identified as a high priority site to research on clusters of landslides and debris flows in a mixed geodynamic setting of active tectonics, seasonal rainfall, river erosion and anthropogenic activities. However, our knowledge about landslide kinematics in this complicated region is still limited. We relied on remote sensing images from one ascending and one descending Sentinel‐1 satellite tracks to constrain the spatial–temporal displacement dynamics of active landslides from 2014 to 2020. The spatial patterns of displacements are determined by thrust faulting, river erosion, and anthropogenic activities. The temporal variations of landslide speed are mainly controlled by the seasonal rainfall rather than the tectonic loading.
... Meanwhile, in highly tectonically active regions, landslides and active faults have been closely related in spatial distribution (Qi et al., 2010;Qi et al., 2021). Some typical landslide movement rates have increased by more than 20% related to the fault activity (Huang et al., 2013;Jiang et al., 2015). Landslide movement rates (LMR) have indicated that more than 70% of global landslides are caused by earthquakes (Broeckx et al., 2020). ...
Landslides are frequent in the Nanpeng River fault zone in southwest Yunnan. Based on a Zhen Qing Expressway survey, the geological conditions and characteristics of landslides in this area were studied. The conclusions are as follows: 1) the geological background was the internal cause of local highly steep slopes and broken rock masses. The main landslide types in study area are fault-type and accumulation landslides. 2) The formation of fault-type landslides is related to endogenous causes, such as tectonic movements, but they are less easily triggered than accumulation landslides. Accumulation landslides are related to broken rock masses and are sensitive to external factors such as rainfall and artificial unloading. 3) The coordinated control of permanent support engineering, local deformation control, and overall support reinforcement should be considered as preventive measures.
... Jiangdingya (Huang et al. 2013;Meng et al. 2013;Meng et al. 2014;Qi et al. 2021aQi et al. , 2021b. In 2010, the Zhouqu debris flow resulted in a serious disaster in which at least 1,756 people perished (Dijkstra et al. 2012). ...
Numerous large-scale fragmented bedrock landslides developed along major fault system is a world-wide phenomenon, which are often characterized with repeated reactivation throughout histories. Due to the large-scale and deep-seated features, it is normally difficult to control such landslides, which in turn pose great threat to local residents and infrastructures. Therefore, monitoring and forecasting these gigantic landslides has become a key protocol for risk reduction. This paper introduces such a typical massive landslide, named Yahuokou landslide, besides Min River in Zhouqu County, Gansu Province, China. Reactivated on July 16, 2019 with a volume of approximately 4×106m3, moving slowly and transitionally starting from top part, its toe had partially blocked the Min River and destroyed roads and houses eventually by August 11, 2019. As to emergency response for such huge slow-moving landslide, there is no standard national protocols. Therefore, how to make effective emergency decision has become a challenge. Based on previous experiences, integrated multi-methods, including UAV imagery interpretation, we applied GNSS monitoring and field investigations in the early stages of landsliding, in order to assist the decision-making. The results show that the movement path of the current displacement is consistent with that of the 1989 reactivation event, and the slide body was separated into three relatively independent blocks with different sliding velocities and responses to rainfall. The upper and lower blocks appeared less affected by rainfall, while the middle block responded more to the changes in precipitations. It proves that the combined approaches using a variety of monitoring techniques can play an effective role in the monitoring of rapidly deformed transitional large-scale landslides, and can also provide a set of reference methods for the emergency disposal of similar landslide hazards.
... The lower part of the Suoertou landslide is a fault fracture zone with a high degree of weathering, and the upper surface layer is silty clay and residual gravel soil (Zhang, 2018). The landslide has been slowly deforming since it was reactivated in the 1970s Chen, 2013;Huang et al., 2013;Li et al., 2013;Zhang, 2012). Figure 8b shows the Sentinel-1 ascending image LOS deformation velocity from October 5, 2017, to December 30, 2018. ...
Zhouqu County in Gansu Province, Northwest China, is typically highly prone to landslides. On July 12, 2018, a landslide blocked the Bailong River near Zhouqu County, posing a serious threat to the life and property of local residents and the safety of infrastructure. Small baseline subset interferometry synthetic aperture radar technology (SBAS-InSAR) was adopted to identify the potential active landslides in the surrounding area of Zhouqu County, using ascending and descending orbit Sentinel-1 satellite images taken from October 2017 to December 2018. The surface deformation areas detected by SBAS-InSAR were verified by optical remote sensing image interpretation and field investigation, and a total of 23 active landslides were identified finally. The deformation characteristics of four typical landslides are analysed in detail using deformation velocity and rainfall data. It is found that the deformation velocity of landslides in this area is mainly affected by rainfall and there is a lag effect. The results can provide a reference for the prevention and control of landslide risk in Zhouqu County.
The NW-SE-striking fault zone in the Bailong River Basin in the northeastern margin of the Qinghai-Tibet Plateau have the most densely distributed, large complex landslides in China. However, the failure of large complex landslides along the fault zone and the causes of their complex geomorphic characteristics are unclear. The purpose of this study was to explore the relationship between the fault zone and the spatial distribution, direction of movement, and geomorphic characteristics of large landslides. We inventoried 29 large landslides in the middle reaches of the Bailong River and described their characteristics. Statistical analysis revealed differences in the spatial relationship between the faults and landslides of different scales. Almost all of the landslide bodies with an area >1 km² are distributed on the faults; in addition, the strike of the faults was found to constrain the direction of movement of the landslides to the WNW-ESE direction. Statistical results show that the cross sections of landslides in the study area are asymmetric arc, corresponding to which there are significant differences in the geomorphological characteristics of the north and south sides of landslides. The geometric characteristics, physical properties (i.e., material weakness) of the fault zone and rapid uplift of the hanging wall were responsible for the asymmetric shape of landslide cross sections and the geomorphic difference. We present a conceptual model based on the relationship between the fault zone and landslides, which facilitates an improved understanding of the relationship between the fault zone and landslide evolution.
A 3-D model of shear fracture in an elastic half-space provides insight into the initiation of sliding along weak pre-existing surfaces in rock or consolidated sediments. An elastic model is justified physically if regions of non-elastic deformation associated with sliding are small relative to the size of the shear fracture. A subsurface elliptical shear fracture parallel to the surface simulates sliding at depth along a pre-existing weakness (e.g. a bedding plane). Based on the stress concentration at the shear fracture perimeter, the model predicts landslide scars will tend to have elliptical shapes in map view and width-to-length values of 0.5–1, consistent with many observations. As a shear fracture spreads, the stress concentration at its perimeter promotes its propagation up towards the surface. The model predicts that sliding at depth causes and precedes fracturing at the surface. For a shear fracture less then twice as long as it is wide, surficial fracturing should start in the head and from there ‘unzip’ down along the slide flanks. Depending on the ambient stress state and the shear strength loss at the slide base, a shear fracture might need to become several or more times wider and longer than its depth to develop a sufficiently intense stress concentration to propagate out of plane to the surface. This accounts for the large length-to-thickness ratios of many natural slides. The model also accounts for the following generic landslide characteristics: a steep, arcuate, concave-downhill head scarp; an echelon pattern of opening-mode fractures along the flanks and subparallel to the head scarp trace; subsidence and normal faulting near the head of a slide; and uplift with thrust faulting near the slide toe.