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Abstract The 2008 Wenchuan earthquake in Sichuan, China, dramatically changed the terrain surface by inducing large numbers of landslides. Due to the lack of adequate pre- and post-earthquake Digital Elevation Models, the landslide volume estimation was done either using empirical area-volume relationships over large areas or by field surveys in a few catchments with debris flow threats. The trend of the change of volume of loose materials in the earthquake affected area over the decade since the earthquake remains largely unknown. In this study we were able to address this issue using nine DEMs taken at different years and from different sensors to study the change in loose material volume caused by co-seismic and post-seismic landslides over a period of 9 years. The area around the towns of Yingxiu and Longchi, for which also multi-temporal landslide inventories were available, was selected for this study. Methods to register the DEMs and minimize their vertically bias were applied. The quality of the DEMs was assessed through GCPs and terrain representation. As could be expected, high resolution DEMs showed more realistic volume estimates than the low resolution ones. The analysis showed that the frequency and magnitude of the landslide volume dynamics decreases significantly after the early post-seismic period, and in the last years human activities became a more dominate factor than mass movements. The post-seismic material loss from 2008 to 2014 was close to the gained volume of the co-seismic landslides, and the depletion of the materials was mostly at the toes of the co-seismic landslides. The analysis was done based on gain and loss calculated from the DEMs, and actual volumes could not be calculated due to unknown failure surface depths of the landslides. Highlights • This research shows the potential and problems of multi-temporal DEM analysis in a post-earthquake environment. • Methods to register DEMs were presented. • The analysis showed that the landslide volume decreased significantly in the first 6 years after the earthquake. • In the early post-seismic stage the elevation changes were majorly caused by mass movement while in the later years human activity became a dominate factor [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]

In the 2008 Wenchuan earthquake, the mass ejection type of high-speed and long-run-out landslide was an unusual hazard characterized by its dramatic phenomenon of a huge slope mass launching into the air and becoming airborne for a long distance. Quantitative and qualitative combined techniques were applied to reveal the formation mechanism of this type of landslide. Four prerequisites critical to form mass ejection are identified: high position of the toe of the surface of rupture, critical height and critical inclination of slope, sufficient open space in the movement direction, and adequate take-off speed of ski-jump-like mass ejection. These four area-specific prerequisites provide a promising approach for screening and targeting the potential landslides. Subsequently, a dynamic reliability analysis method that considers the feature of energy–time distribution is proposed. This site-specific method provides a more credible evaluation by emphasizing the most significant period within the whole earthquake duration. Finally, an aerodynamic inverse method combined with an energy-conservation-based method is applied in the quantitative evaluation to calculate take-off speed of mass ejection. This paper provides a viable solution for regional screening and site assessment for new potential targets of this type of landslide. [ABSTRACT FROM AUTHOR]

This paper studies the run-out of earthquake-induced landslides. There are more than 20 mechanical models to explain long run-out of rapid landslides including some earthquake-induced landslides. However, notably few of them considered the effect of seismic loading on the run-out of landslides. In a previous study, we have proposed a model, which is called the multiplex acceleration model (MAM), to interpret the long run-out mechanism, and a shaking-table test has been performed to verify the MAM. Because the previous MAM is a conceptual model and only a single stone has been examined under sine waves by the shaking-table test, the MAM needs to be extended and further verified. In this paper, the MAM was extended by introducing the movement change that was induced by the so-called trampoline effect of earthquake loading, and the latest practical numerical simulation program, discontinuous deformation analysis (DDA), was used to verify the mobility of earthquake-induced landslides. After a conceptual landslide model was used to verify the effect of seismic loading on the mobility, the Donghekou landslide, which was a typical long run-out landslide that was induced by the 2008 Wenchuan earthquake, was analyzed. The results show that: the seismic loading could be one of the factors that could eventually help increase the run-out of landslides. [ABSTRACT FROM AUTHOR]

Abstract: Permanent sliding displacement represents a common damage parameter for evaluating the seismic stability of slopes. Recently developed empirical models for the sliding displacement of shallow (rigid) sliding masses have demonstrated that including multiple ground motion parameters in the predictive model (e.g., peak ground acceleration and peak ground velocity) improves the displacement prediction and reduces it uncertainty. A unified framework is developed that extends these empirical displacement models for application to flexible sliding masses, where the dynamic response of the sliding mass is important. This framework includes predicting the seismic loading for the sliding mass in terms of the maximum seismic coefficient (kmax) and the maximum velocity of the seismic coefficient-time history (k–velmax). The predictive models are a function of the peak ground acceleration (PGA), peak ground velocity (PGV), the natural period of the sliding mass (Ts), and the mean period of the earthquake motion (Tm). The empirical predictive models for sliding displacement utilize kmax and k–velmax in lieu PGA and PGV, and include a term related to the natural period of the sliding mass. This unified framework provides a consistent approach for predicting the sliding displacement of rigid (Ts =0) and flexible (Ts >0) slopes. [Copyright &y& Elsevier]

Abstract: The influence of site effects on landslide triggering during earthquakes has been inferred in several studies, but its evaluation is made difficult by the complexity of factors controlling the dynamic response of potentially unstable slopes and also by the lack of local ground motion instrumental observations. This work explores this problem and reports new findings based on an ongoing long term accelerometric monitoring conducted on a landslide-prone test area in the Apennine Mountains, Italy, where the presence of site effects enhancing seismic susceptibility of local slopes has been invoked on the basis of historic accounts of landsliding triggered at large epicentral distance. The recordings relative to low-to-moderate magnitude earthquakes showed significant amplifications affecting hillslope portions covered by thick (>5m) colluvia and pronounced amplification maxima oriented along the local maximum slope direction on a recent deep-seated landslide. While the amplifications seem most likely linked to high impedance contrast between surface materials and underlying substratum, the causes of directivity are less clear. The case of the monitored test site together with evidence of site response directivity identified on other hillslopes, suggest that the directivity phenomena can result from a combination of topographic, lithological and structural factors that act together to re-distribute shaking energy, focusing it on site-specific directions. Thus, it is difficult to single out the critical factors controlling such phenomena and no general criterion for the identification of sites affected by directivity is proposed here. Nevertheless, the presence and orientation of site response directivity can be revealed through reconnaissance techniques by using recordings of seismic weak motion and/or ambient microtremors, and calculating azimuthal variation of shaking energy and horizontal-to-vertical ground motion spectral ratios. A comparison with the recordings obtained during the recent MW =6.3 earthquake that hit the Abruzzo region in April 2009 demonstrated that analysis relying on data from low energy events can furnish valid indications for slope behaviour also under stronger shaking, provided the data are well differentiated in terms of distance, azimuth and source characteristics. Furthermore, the comparative analysis of the Abruzzo earthquake recordings at a landslide and reference sites showed that directivity properties of strong shaking had been correctly anticipated using earlier weak motion observations. However, under the complex slope conditions the identification of resonance frequencies from horizontal-to-vertical spectral ratios estimated from weak-motion accelerometric recordings does not seem reliable, and better results have been obtained by velocimetric microtremor recordings. [Copyright &y& Elsevier]

Abstract: During the twentieth century, several methods to assess the stability of slopes during earthquakes were developed. Pseudostatic analysis was the earliest method; it involved simply adding a permanent body force representing the earthquake shaking to a static limit-equilibrium analysis. Stress-deformation analysis, a later development, involved much more complex modeling of slopes using a mesh in which the internal stresses and strains within elements are computed based on the applied external loads, including gravity and seismic loads. Stress-deformation analysis provided the most realistic model of slope behavior, but it is very complex and requires a high density of high-quality soil-property data as well as an accurate model of soil behavior. In 1965, Newmark developed a method that effectively bridges the gap between these two types of analysis. His sliding-block model is easy to apply and provides a useful index of co-seismic slope performance. Subsequent modifications to sliding-block analysis have made it applicable to a wider range of landslide types. Sliding-block analysis provides perhaps the greatest utility of all the types of analysis. It is far easier to apply than stress-deformation analysis, and it yields much more useful information than does pseudostatic analysis. [Copyright &y& Elsevier]

Abstract: Although, thanks to the new developments in investigation techniques, modeling, and data analyses, much progress has been made in our understanding of collateral seismic hazards, important new lessons are still being learned from historic and recent earthquakes. By referring to the accompanying papers included in this Special Issue and other recent literature, we present an overview of current issues and future challenges of research on earthquake, triggered landsliding. We also offer some recommendations for future research priorities, as a proposed starting point for the next generation of research on earthquake-induced slope failures. These include i) the compilation of many more complete seismic landslide inventories with adequate contextual information, as well as of retrospective inventories; ii) the improvement of regional-scale assessments of seismic landslide susceptibility and hazard; iii) the development of new methods for regional scale analysis of hazards from large catastrophic landslides; and iv) the long-term monitoring of representative test slopes instrumented with an array of accelerometer stations. [Copyright &y& Elsevier]

Abstract: A new comprehensive areal model of earthquake-induced landslides (CAMEL) has been developed to assist in planning decisions related to disaster risk reduction. CAMEL provides an integrated framework for modeling all types of earthquake-induced landslides using fuzzy logic systems and geographic information systems. CAMEL is designed to facilitate quantitative and qualitative representation of terrain conditions and knowledge about these conditions on the likely areal concentration of each landslide type. CAMEL has been empirically evaluated with respect to disrupted landslides (Category I) using a case study of the 1989 M =6.9 Loma Prieta, CA earthquake. In this case, CAMEL performs best in comparison to disrupted slides and falls in soil. For disrupted rock fall and slides, CAMEL''s performance was slightly poorer. The model predicted a low occurrence of rock avalanches, when none in fact occurred. A similar comparison with the Loma Prieta case study was also conducted using a simplified Newmark displacement model. The area under the curve method of evaluation was used in order to draw comparisons between both models, revealing improved performance with CAMEL. CAMEL should not however be viewed as a strict alternative to Newmark displacement models. CAMEL can be used to integrate Newmark displacements with other, previously incompatible, types of knowledge. [Copyright &y& Elsevier]

• Slope stability is a critical consideration for superstructures and infrastructures. • Estimation of the earthquake-triggered landslide displacement is one of the most important topics of slope engineering. • Newmark sliding block model is a widely used method for predicting earthquake-induced ground displacement. • A new useful and more appropriate regression equation has been obtained to estimate the Newmark displacement. Landslides are one of the most important results of earthquakes. Estimation of the earthquake-triggered landslide displacement is a major topic for engineering because the amount of ground displacement is significant for seismic hazard assessment. Newmark sliding block model is a method commonly used to estimate earthquake-induced ground displacements. Based on this method some regression analyses have been carried out and different equations have been obtained. In this study, primarily, previous studies have been updated according to significant world wide earthquake records (2307 strong ground motion records belonging to 26 earthquakes). Then, in scope of this paper, a new regression equation has been obtained and the results have been examined. In consequence of the comparisons, it has been determined that the new formula has more appropriate results in terms of the regression parameters (R2 and standard deviation). All of these regression equations are suitable for a general approximation to the topic. These equations are useful to predict the amount of displacement for regionalscale seismic landslide hazard but they are not proposed for spesific design. [ABSTRACT FROM AUTHOR]