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Numerous interbedded rock (IR) slopes fail during the Wenchuan earthquake in the mountainous region of western China. Landslides are also triggered in IR slopes with a 60° layer inclination, which are generally stable in gravity-dominant environments. This study examines the effect of seismic motion on the response characteristics and failure patterns of IR slopes with steep layers to develop a landslide hazard assessment tool for earthquake-prone regions. First, we use a centrifuge shaking table test to model the failure process and acceleration responses of two IR slope models with stratigraphic dips of 60° and 80°, respectively, under different seismic intensities. Next, we adopt the Particle Flow Code to examine the crack propagation features and peak ground acceleration amplification effects for the IR slopes. We find that the seismic failure pattern of IR slopes depends largely on rock layer inclination: buckling failure is triggered when rock layers are parallel or nearly parallel to the slope surface, while toppling failure is triggered when the rock layer inclination is significantly higher than that of the slope surface. Following seismic excitation, the damage is mainly observed in the weak rock layers, creating lateral stress on adjacent strong rocks, which undergoes deformation and ultimate macroscopic failure. Further, displacement of the IR slope is negatively correlated to rock layer inclination. Rock layer thickness has a major influence on the damaged area inside the slope mass, while rock layer stiffness mainly affects the deformation distribution near the slope shoulder. • Interbedded slopes with steep layers under earthquake exhibit buckling or toppling. • Using centrifugal shaking table test to reproduce interbedded rock slope failures. • Non-uniform deformation is highly developed in interbedded slopes. • Rock layer inclination is a significant factor on failure type in interbedded slopes. [ABSTRACT FROM AUTHOR]

The Xinmo landslide slope in Sichuan, China, was stable during the intensive Wenchuan Earthquake in 2008 but failed on June 24, 2017. Landslide debris buried Xinmo Village and blocked the Songpinggou River at the slope toe. This study aims to clarify the post-failure behavior of the landslide using two-dimensional discontinuous deformation analysis (2D DDA). The simulation results provide comprehensive information on the initiation and the evolution of the landslide. The failure process determined by the DDA correlates well with the seismic signal analysis results. In addition, the location of the calculated rock deposit is similar to that shown by the topographic map after the landslide. The maximum rock velocity in the landslide is 65.4 m/s. Therefore, the impacts of the high-velocity blocks and the buildings in Xinmo Village must be considered to simulate the burial of Xinmo Village by rocks and the transport of additional rocks across the Songpinggou River. This Xinmo landslide study demonstrates that the DDA accurately simulates the post-failure behavior and determines the impact area of a landslide with complicated failure processes and topography. [ABSTRACT FROM AUTHOR]

Regional active tectonics and historical earthquake records indicate the importance of the triggering effects of historical strong earthquakes on groups of large-scale landslide occurrences in the Wei River midstream section. In this study, a method to assess the triggering effects of historical earthquakes on regional large-scale landslides is presented. The greatest epicentral distances of seismically induced landslides were calculated. The triggering effects of four key historical strong earthquakes with epicenters within 300 km of the Wei River midstream section were analyzed; these are the M s 7.0 Qishan earthquake of 780 BCE, the M s 8.0 Tianshui earthquake of 1654 CE, the M s 8.25 Huaxian earthquake of 1556 CE, and the M s 8.5 Haiyuan earthquake of 1920 CE. Taking the Qishan earthquake as an example, a seismically induced landslide displacement and hazard assessment method based on the Newmark displacement model was developed. The degree of spatial matching of the results for historical-earthquake-triggered landslides and the distribution of actual large-scale landslide deposits were compared quantitatively using the success rate curve method. The results show that of the four historical earthquakes, the Tianshui earthquake had the strongest effect of inducing large-scale landslides regionally along the Wei River midstream section. [ABSTRACT FROM AUTHOR]

Catastrophic debris flows are frequently triggered by rainstorms after the 2008 Wenchuan earthquake and pose great threats to residential buildings and human lives in the mountainous areas. However, little effort has been devoted to studying the quantitative assessment of the physical vulnerability of buildings to debris flows in the Wenchuan earthquake-affected areas. To cope with this deficiency, this paper presented a quantitative method to assess the physical fragility of buildings related to debris flows by analyzing the debris flow activity and building damage features. First, we constructed a building database in the area affected by the Cutou debris flow and determined the degree of damage to each building. Then, the momentum flux was selected as a debris flow intensity parameter, considering the combined effect of flow velocity and flow depth. We used the FLO-2D software to reproduce the process of the debris flow that occurred on 20 August 2019 in the Cutou gully and obtained the intensity parameters of the debris flow. Finally, we proposed physical fragility curves for different types of building structures to the debris flow based on the model describing the probability of exceeding different damage states corresponding to different intensities of debris flows. In the case of brick-concrete buildings, when the momentum flux was 8 m3/s2, buildings were moderately damaged at the probability P = 1 with a 95% confidence interval, and complete damage was sustained from a momentum flux of 36 m3/s2. Masonry-wood buildings sustained complete damage from a momentum flux of 5 m3/s2. The structural resistance of buildings to debris flows in the Wenchuan earthquake-affected region can be assessed by using the proposed physical fragility functions, which provide a scientific basis for risk management and mitigation strategies. • We constructed the building database and analyzed damage characteristics. • The intensity process of the debris flow was reproduced by FLO-2D software. • The fragility curves were developed by numerical simulation and the probability model. • Masonry-wood buildings will sustain complete damage from the momentum flux of 5 m3/s2. • Brick-concrete buildings will sustain complete damage from the momentum flux of 36 m3/s2. [ABSTRACT FROM AUTHOR]

Abstract: Effects from the disastrous Ms 8.0 Wenchuan Earthquake of May 12, 2008 show that the seismic hazard is closely related to the proximity of active faults and elevated areas of unstable rock as well as the recurrence rate of large earthquakes. Dextral-slip thrusting in the Longmenshan Mountains formed large displacement along ~250km of the Central Longmenshan Fault and smaller offsets along sub-parallel faults. The distribution pattern of the major destruction has a strong northeast–southwest orientation closely related to the ruptured faults and decreases noticeably 3–5km away from the Central Longmenshan Fault and ~2km from the other faults. Thousands of landslides, rock falls and debris flows triggered by the earthquake lie chiefly adjacent to the principal fault, and smaller-scale landslides along the other faults as well as in distant areas. Some landslides formed dams whose impounded waters threatened downstream cities. Future landslides, rock falls and debris flows will result from rock loosened by the earthquake during rainy seasons or subsequent earthquakes. The Central Longmenshan Fault had maximum displacements of 4.6m dip-slip and 6.1m dextral-slip and the total dip and dextral-slip displacement for all faults is 5.9m and 7.0m, respectively. These faults apparently converge at depth and account for the crustal shortening in the region. Their displacements coupled with convergence rates determined by GPS measurements provide an estimated recurrence interval for an Ms 8.0 earthquake along the Central Longmenshan Fault of between 4600 and 6600years and that for the entire Longmenshan Mountains between 1000 and 3000years. [Copyright &y& Elsevier]

The evaluation of seismic site amplification and its relationship with geological structures play a vital role in earthquake engineering and hazard assessment. This study presents an analysis of topographic and geologic site amplification effects observed in the Qiaozhuang region, Sichuan Province, China. Seismic recordings at several monitoring stations installed on two slopes located at a distance of about 1 km in the study area after the 2008 Wenchuan earthquake provide evidence of strong and variable amplifications. To assess the combined effect of topographic and geological controls in slope response to seismic motions, we built 2D and 3D dynamic numerical models using monitoring data as inputs. Four layers with different P-wave velocities, based on geophysical survey in the study area, are considered in the numerical models. Models that only consider topography give an amplification factor of <3, which is much lower than the amplification factor of 5–6 from the monitoring data, while those models that considered both the topographic variation and four layers agree well with the monitoring data. The 3D modeling results show that the subsurface amplification factor is less than that on the slope surface even at the same elevation. This is also consistent with the monitoring data and further indicates that the combined topographic and geological amplification effect on the slope surface is more significant than the sole geological amplification effect inside the slope. Our numerical simulation results suggest that it is important to consider the combined topographic and geological amplification effects in the hazard assessment of seismically induced slope failures. • This study presents long-term monitoring data of slope seismic response. • Homogeneous numerical models show that topography alone only produces low amplification effects. • The results from three-layer heterogenous 3D model indicat the importance of geological amplification effect. [ABSTRACT FROM AUTHOR]

A probabilistic framework that considers the variability and uncertainty of the ground motions caused by earthquakes and the parameters of the slope material is proposed to assess the seismic stability of rock slopes. A stochastic ground motion simulation method, which reflects certain earthquake scenarios and site characteristics, was used to generate accelerograms as seismic inputs. Then, the probabilities of failure (P f) of the slopes when subjected to earthquake ground motions were computed via Monte-Carlo simulations based on the simulated ground motions and the decoupled Newmark permanent-displacement analysis. An example rock slope was used to illustrate the proposed procedure and verify its rationality. The results showed that the magnitudes of the earthquakes and the source-to-site distances had significant influences on the seismic stability of the slopes. For an earthquake of the same magnitude, the P f of the slope decreased rapidly as the source-to-site distance increased. In addition, given the same source-to-site distance, the P f of the slope increased steadily as the magnitudes of the earthquakes increased. Also, it was found that the influence of coefficient of variation of the slope's shear strength parameters (i.e., c , φ) was not negligible when the uncertainty of earthquakes was not considered. However, it may be overshadowed by the significant influence of a great earthquake, especially when the variability of ground motions is taken into account. The results that were obtained agreed well with observed earthquake-induced landslide phenomena and the statistical data of two typical earthquakes that occurred in Japan and China, which implies that the proposed method is accurate. • A probabilistic approach to assess rock slope seismic stability is proposed. • The uncertainties associated with earthquakes and slope were considered simultaneously. • Influence of earthquake and variability of slope's strength parameters was investigated. • The results agreed well with the observed earthquake-induced landslide phenomena. [ABSTRACT FROM AUTHOR]

Catastrophic debris flows are common after large earthquakes and pose a significant risk for recovering communities. The depositional volume of these large debris flows is often much greater than the initiation volume, suggesting that bulking of the flow plays an important role in determining their volume, speed, and runout distance. Observations from recent earthquakes have driven progress in understanding the relationship between triggering rainfall events and the timing of post-earthquake debris flows. However, we lack an adequate mechanism for quantifying bulking and applying it within a hazard context. Here we apply a 2D dynamic debris flow model (Massflow) that incorporates a process-based expression of basal entrainment to understand how debris flow bulking may occur within post-earthquake catchments and develop hazard maps. Focussing on catchments in the epicentral area of the 2008 M w 7.9 Wenchuan Earthquake, we first parameterised the model based on a large debris flow that occurred within the Hongchun catchment, before applying the calibrated model to adjoining catchments. A model sensitivity analysis identified three main controls on debris flow bulking; the saturation level of entrainable material along the flow pathway, and the size and position of initial mass failures. The model demonstrates that the difference between small and very large debris flows occur across a narrow range of pore-water ratios (λ). Below λ = 0.65 flows falter at the base of hillslopes and come to rest in the valley bottom, above λ = 0.70 they build sufficient mass and momentum to sustain channelised flow and transport large volumes of material beyond the valley confines. Finally, we applied the model across different catchments to develop hazard maps that demonstrate the utility of Massflow in post-earthquake planning within the Wenchuan epicentral region. • Focussing on the Wenchuan region in China, we apply a 2D dynamic debris flow model (Massflow) • We use Massflow's process-based expression of basal entrainment to examine debris flow bulking • We find a narrow range of pore-water ratios (λ) mark the difference between small and large debris flows • Finally, we applied the model across different catchments to develop hazard maps [ABSTRACT FROM AUTHOR]