Landslides occur frequently in China. Especially, in the western part of China, large-scale landslides are notable for their scale, complex formation mechanism, and serious destruction. This paper ...presents some typical large-scale landslides that occurred in the southwest of China since the beginning of the twentieth century but were rarely reported worldwide. These cases represent different geological conditions and different triggering factors and mechanisms. The analysis shows that about 80% of large-scale landslides occurred in the first slope-descending zone along the eastern margin of Tibet Plateau, which is tectonically very active. The intensive interactions between the endogenic and epigenetic geological process cause serious dynamic change on the high steep slope and then result in the development of large-scale landslides. Strong earthquakes are also common in this area, and repetitive seismic activities make the slopes unstable and more vulnerable to failures. Besides earthquake, the area also experiences high rainfall, which is also responsible for triggering some of the large landslides.
Large-scale landslides in western China are famous for their size, complex formation mechanism and serious destruction. Data were collected from some typical large-scale landslides in mainland China ...in the 20th century. A number of geo-mechanical models have been identified: the “three sections” model (sliding; tension cracking; shearing), “retaining wall collapse”, “horizontal-pushing” in horizontal strata; large-scale toppling in counter-inclined strata; the creep-bending–shearing model etc. Large-scale rock landslides are generally accompanied by sudden brittle failure of the “locking section” along the potential sliding surface. The paper discusses the importance of this “locking section” which is key to assessing slope geohazard and to the development of control/mitigation measures.
Numerous empirical equations have been proposed to estimate the joint roughness coefficient (JRC) of a rock fracture based on its fractal dimension (D). A detailed review is made on these various ...methods, along with a discussion about their usability and limitations. It is found that great variation exists among the previously proposed equations. This is partially because of the limited number of data points used to derive these equations, and partially because of the inconsistency in the methods for determining D. The 10 standard profiles on which most previous equations are based are probably too few for deriving a reliable correlation. Different methods may give different values of D for a given profile. The h–L method is updated in this study to avoid subjectivity involved in identifying the high-order asperities. The compass-walking, box-counting and the updated h–L method are employed to examine a larger population of 112 rock joint profiles. Based on these results, a new set of empirical equations are proposed, which indicate that the fractal dimension estimated from compass-walking and the updated h–L method closely relate to JRC, whereas the values estimated from box-counting do not relate as closely.
•Using fractals to estimate JRC is reviewed with discussion about limitations.•Previously published equations may misestimate the JRC of a rock profile.•Different methods give different Ds and different correlations of JRC with D.•The h–L method for the determination of D is modified and updated.•New correlations are proposed based on examination of 112 joint profiles.
The Daguangbao landslide was the most catastrophic mass movement triggered by the 2008 Wenchuan earthquake with a magnitude scale of Ms. 8.0. The landslide, which was 4.6 km long and 3.7 km wide, had ...a volume of approximately 1.2 × 109 m3. Since its occurrence, many assumptions regarding its initiation and movement mechanisms have been made; however, the mechanisms remain unclear. Our recent field evidence suggested that the Daguangbao landslide occurred along a saturated fault parallel to the bedding in the Paleozoic carbonate strata. We therefore examined whether the shear behavior of the fault material could have favored the initiation and movement of the Daguangbao landslide. First, we performed monotonic and cyclic loading tests on samples taken from the bedding fault breccia using ring-shear apparatus. We then conducted Newmark displacement analysis to examine the initiation and motion of the landslide. The laboratory results showed that the carbonate fault breccia on the sliding layer of the landslide has a high liquefaction potential and the friction coefficient at its steady-state under undrained condition could be as small as 0.04. We also found that with increase of shear displacement, the friction coefficients can at first exponentially increase to the peak-failure value and then exponentially decrease to the steady-state value. These relationships between the friction and shear displacements were incorporated in the Newmark analysis of landslide initiation and motion. The numerical calculation results showed that the landslide occurred 36 s after the 2008 Wenchuan earthquake origin time (at its hypocenter), and the landslide mass, with a speed of 94 m/s, collided with a riverbank in the 76th second. We infer that, in addition to the strong seismic force, pore-water pressure built up within the bedding fault during the seismic shaking, enhancing the instability of the Daguangbao slope, and a further increase of pore-water pressure with progress of sliding elevated the mobility of the landslide.
•Displacement-dependent sliding strengthening and weakening friction laws are obtained based on ring shear tests•Initiation mechanism of the Daguangbao landslide is proposed based on Newmark displacement analysis•Buildup of high pore-water pressure within the sliding surface enhanced the initiation and mobility of the Daguangbao landslide
Large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking. Most moderate‐ and large‐magnitude earthquakes trigger landslides, ranging from ...small failures in the soil cover to massive, devastating rock avalanches. Some landslides dam rivers and impound lakes, which can collapse days to centuries later, and flood mountain valleys for hundreds of kilometers downstream. Landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows. Cracks and fractures can form and widen on mountain crests and flanks, promoting increased frequency of landslides that lasts for decades. More gradual impacts involve the flushing of excess debris downstream by rivers, which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency, settlements, ecosystems, and infrastructure. Ultimately, earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales. Two recent events have attracted intense research into earthquake‐induced landslides and their consequences: the magnitude M 7.6 Chi‐Chi, Taiwan earthquake of 1999, and the M 7.9 Wenchuan, China earthquake of 2008. Using data and insights from these and several other earthquakes, we analyze how such events initiate processes that change mountain landscapes, highlight research gaps, and suggest pathways toward a more complete understanding of the seismic effects on the Earth's surface.
Plain Language Summary
Strong earthquakes in mountainous regions trigger chains of events that modify mountain landscapes over days, years, and millennia. Earthquake shaking can cause many tens of thousands of landslides on steep mountain slopes. Some of these sudden slope failures can block rivers and form temporary lakes that can later collapse and cause huge floods. Other landslides move more slowly, in some cases in a stop‐start fashion during heavy rains or earthquake aftershocks. Debris from these landslides can clog channels, and during heavy rainfall, the debris can be transported downstream for many kilometers with catastrophic consequences. New landslides tend to happen more frequently than usual for months to years following an earthquake because the strong ground shaking has fractured and weakened the slopes. Other effects of large earthquakes can last, in various forms, over geologic time scales. Over the past two decades, our understanding of these issues has advanced because of the detailed study of the 1999 Chi‐Chi earthquake in Taiwan and the 2008 Wenchuan earthquake in China. We compile and discuss the results of research on these and other earthquakes and explain what we have learned, what we still need to know, and where we should direct future studies.
Key Points
Coupled surface processes initiated by strong seismic shaking are important hazards in mountain landscapes
Earthquake‐induced landslides pose challenges to hazard and risk assessment, management, and mitigation
Multidisciplinary approaches further the understanding of the earthquake hazard cascade, yet challenges remain
The Ms 8.0 Wenchuan earthquake on May 12, 2008 triggered tens of thousands of landslides and produced large amounts of loose material. The loose material accumulated in gullies or on slopes provides ...abundant sources for the consequent debris flows, which will endanger resettled residents and destroy urban reconstruction. During the 5years following the Wenchuan earthquake event, heavy rainfalls have already induced a great number of debris flows in the earthquake-damaged area, resulting in serious casualties and property losses. The co-seismic landslides and the debris flows induced by rainfalls in the Mianyuan River basin are analyzed using multi-temporal remote sensing images. More than 2000 landslides were triggered and about 4.0×108m3 of loose material was generated in the Mianyuan River basin, and the volume of erodible material is 6.0×107–1.6×108m3. There were 1.27×107m3 of bed load sediments and 6.3×105m3 suspended load sediments transported into the river system in the past 5years. The active mass movements will last for a long period in the Mianyuan River basin.
•Characteristics of post-seismic landslides following the 2008 Wenchuan earthquake•2259 landslides mapped in the Mianyuan River basin, with a volume of 4.0×108m3•The volume of erodible material is 6.0×107–1.6×108m3 in the Mianyuan Riverbasin.•Only 1.27×107m3 of bed load has been transported into the Mianyuan River.•Active mass movements will last for a long period in the Mianyuan River basin.
Strong earthquakes, especially in continental mountainous areas, can trigger extensive mass wasting, producing large amounts of debris that accumulates along the hillslopes or in drainage channels. ...The coseismic deposits and disturbed slopes are prone to be reactivated or remobilized by heavy rainfalls in the subsequent years after the earthquake. Predicting how long post-seismic landslide activity will return to the pre-earthquake level is a key to risk assessment and management. However, this is still poorly understood, and lacks quantitative prediction approach. The 2008 Wenchuan earthquake triggered an unprecedented number of landslides, creating an extraordinary natural laboratory to investigate the evolution of post-seismic landslides and their impacts on environment. Using the vegetation recovery rate as an indicator, we present the observational evidence of the post-seismic landslide evolution based on MODIS NDVI time series between 2000 and 2018. Using a simple vegetation recovery rate (VRR) function, we quantify the rate of vegetation regrowth in the Wenchuan earthquake affected area, and discuss the decaying trend of post-seismic landslide activities. Our findings show that 83% of the co-seismic landslides become inactive within a decade. The NDVI trend suggests that landslide activity may return to the pre-earthquake level within 18 years. The sensitivity of vegetation regrowth to post-seismic landsliding thus offers a great potential to improve our understanding of the spatio-temporal evolution of the post-seismic landslide activities.
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•First decadal time series analysis is carried after 2008 Wenchuan Mw 7.9 earthquake.•NDVI0 is proposed to minimize uncertainty in the vegetation damage area estimation.•Vegetation recovery rate function is used to locate active and inactive landslides.•Recovery of vegetation to the pre-earthquake level is expected within 18 years.
The behavior of reactivated and first‐failure landslides after large displacements is controlled by the available shear resistance in a shear zone and/or along slip surfaces, such as a soil‐bedrock ...interface. Among the factors influencing the resistance parameter, the dependence on the shear rate can trigger catastrophic evolution (rate‐weakening) or exert a slow‐down feedback (rate‐strengthening) upon stress perturbation. We present ring‐shear test results, performed under various normal stresses and shear rates, on clayey soils from a landslide shear zone, on its parent lithology and other lithologies, and on clay‐rock interface samples. We find that depending on the materials in contact, the normal stress, and the stress history, the shear‐rate‐dependent behaviors differ. We discuss possible models and underlying mechanisms for the time‐dependent behavior of landslides in clay soils.
Plain Language Summary
The occurrence and behavior of landslides depend on a number of geologic, climatic, and anthropic factors. Among them, the resistance of the deforming material plays a fundamental role. It is controlled by various parameters, such as the mineral composition of the soil or rock and its structure, the pressure and chemistry of the water filling the pores, the temperature and deformation rate at which the movement occurs. We present the results of laboratory experiments in which we simulate the landslide condition by shearing, one against the other, samples of a clayey soil, of the rock from which the soil derives and of other rocks, or samples made for one half by soil and for the other half by rock. We use samples from the shear zone of a real landslide, and we show that the behaviors of various material assemblies, when sheared at different velocities, are different: the strength can both increase or decrease with the shear velocity. We also show that the pressure we apply to the samples—to simulate landslides of different depths, or different water pressures within the pores—and the compression history can affect the behavior.
Key Points
A clayey soil, various rocks, and soil‐rock interfaces have been sheared at rates and normal stresses typical of landslides
The sample assemblies showed different shear‐rate‐dependent patterns, related also to mineralogy, normal stress, and stress history
The observed patterns may lead to different behaviors and evolutions in landslides
The 2008 Mw 7.9 Wenchuan Earthquake (Sichuan, China) was possibly the largest and most destructive recent earthquake as far as the geo-hazards are concerned. Of the nearly 200,000 landslides ...triggered originally, many remobilized within a few years after the initial event by rainfall, which often caused catastrophic debris flows. The cascades of geo-hazards related to the Wenchuan Earthquake motivated research worldwide to investigate the triggering and mechanisms of co-seismic landslides, their rainfall-induced remobilization, the generation of debris flows, the evolution of their controlling factors, and the long-term role of earthquakes in shaping the topography. On the eve of the 10th anniversary of the 2008 Wenchuan Earthquake, we present a short review of the recent advances in these topics, discuss the challenges faced in the earthquake-related geo-hazards mitigation practice, and suggest priorities and guidelines for future research.
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