Structural geology of large (ancient) rockslides - an indicator for a seismic or climatic origin?

2020 ◽  
Author(s):  
Emilie Lemaire ◽  
Anne-Sophie Mreyen ◽  
Hans-Balder Havenith
Keyword(s):  
Structural Geology ◽  
Rock Slope ◽  
Structural Characteristics ◽  
Mass Movement ◽  
Source Zone ◽  
Slope Failures ◽  
Study Results ◽  
The Alps ◽  
The Stability ◽  
Seismic Origin

<p>The stability of rock slopes is often guided by the structural geology of the rocks composing the slope. Geological structures, such as ductile folds, discontinuities as well as brittle faults and fractures, are known factors contributing to a decrease in slope stability according to their orientation in space - with respect to the general orientation of the main slope and its (seismo-) tectonic damage history. Additionally, a rock slope may undergo many forms of gravitationallyinduced, erosional and/or weathering-induced destabilisation.</p><p>Rock slope failures may be classified and described according to several factors, such as their volume, displacement mechanisms and velocity. In this work, especially deep-seated and very large failures (with a volume of >10<sup>7</sup> m<sup>3</sup>) are analyzed with regard to their structural characteristics.</p><p>Giant rockslides originate as planar, rotational, wedge, compound, or irregular slope failures. Most of them convert into flow-like rock avalanches during emplacement. Here, we will not detail the evolution of rock slope failures but rather focus on their origin. The main goal is to identify features allowing to distinguish seismic trigger modes from climatic ones, notably on the basis of the source zone rock structures. We will present examples of classical anti-dip slope (and along-strike) rock structures that hint at a seismic origin, but we will also consider a series of mixed structural types, which are more difficult to interprete. This morpho-structural study is supported by numerical modelling results showing that seismic shaking typically induces deeper seated deformation in initially ‘stable’ rockslopes.</p><p>For failures only partially triggered by dynamic shaking, these study results could help to identify the seismic factor in slope evolution. Especially in less seismically active mountain regions, such as the Alps and the Carpathian Mountains, these analyses can be used for paleoseismic studies – provided that dating the seismic initiation of mass movement is possible. For instance, we will show that the “Tamins” and the “Fernpass” rockslides in the Alps present structural and morphological features hinting at a partly seismic origin. Furthermore, we present study cases of ancient rockslides in the SE Carpathians (“Balta” and “Eagle’s Lake”), where a pure seismic origin is most probable and currently under discussion (supported by numerical analyses).</p>

scholarly journals Analysis of the Influence of Structural Geology on the Massive Seismic Slope Failure Potential Supported by Numerical Modelling

Geosciences ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 323
Author(s):  
Emilie Lemaire ◽  
Anne-Sophie Mreyen ◽  
Anja Dufresne ◽  
Hans-Balder Havenith
Keyword(s):  
Structural Geology ◽  
Numerical Modelling ◽  
Slope Failure ◽  
Rock Slope ◽  
Tien Shan ◽  
Source Zone ◽  
European Alps ◽  
Rock Slopes ◽  
Slope Failures ◽  
Seismic Origin

The stability of rock slopes is often guided significantly by the structural geology of the rocks composing the slope. In this work, we analysed the influences of structural characteristics, and of their seismic responses, on large and deep-seated rock slope failure development. The study was focused on the Tamins and Fernpass rockslides in the European Alps and on the Balta and Eagle’s Lake rockslides in the southeastern Carpathians. These case studies were compared with catastrophic rock slope failures with ascertained or very likely seismic origin in the Tien Shan Mountains. The main goals was to identify indicators for seismically-induced rock slope failures based on the source zone rock structures and failure scar geometry. We present examples of failures in anti-dip slopes and along-strike rock structures that were potentially (or partially) caused by seismic triggering, and we also considered a series of mixed structural types, which are more difficult to interpret conclusively. Our morpho-structural study was supported by distinct element numerical modelling that showed that seismic shaking typically induces deep-seated deformation in initially “stable” rock slopes. In addition, for failures partially triggered by dynamic shaking, these studies can help identify the contribution of the seismic factor to slope instability. The identification of the partial seismic origin on the basis of the dynamic response of rock structures can be particularly interesting for case histories in less seismically active mountain regions (in comparison with the Andes, Tien Shan, Pamirs), such as in the European Alps and the Carpathian Mountains.

scholarly journals Locating rock slope failures along highways and understanding their physical processes using seismic signals

2021 ◽  
Vol 9 (3) ◽  
pp. 505-517
Author(s):  
Jui-Ming Chang ◽  
Wei-An Chao ◽  
Hongey Chen ◽  
Yu-Ting Kuo ◽  
Che-Ming Yang
Keyword(s):  
Slope Failure ◽  
Rock Slope ◽  
Scaling Law ◽  
Mass Movement ◽  
Volume Estimation ◽  
Seismic Signals ◽  
Slope Failures ◽  
Physical Processes ◽  
Seismic Parameters ◽  
Duration Magnitude

Abstract. Regional monitoring of rock slope failures using the seismic technique is rarely undertaken due to significant source location errors; this method also still lacks the signal features needed to understand events of this type because of the complex mass movement involved. To better comprehend these types of events, 10 known events along highways in Taiwan were analyzed. First, a hybrid method (GeoLoc) composed of cross-correlation-based and amplitude-attenuation-based approaches was applied, and it produced a maximum location error of 3.19 km for the 10 events. We then analyzed the ratio of local magnitude (ML) and duration magnitude (MD) and found that a threshold of 0.85 yields successful classification between rock slope failure and earthquake. Further, GeoLoc can retrieve the seismic parameters, such as signal amplitude at the source (A0) and ML of events, which are crucial for constructing scaling law with source volume (V). Indeed, Log(V) = 1.12 ML + 3.08 and V = 77 290 A00.44 derived in this study provide the lower bound of volume estimation, as the seismic parameters based on peak amplitudes cannot represent the full process of mass loss. Second, while video records correspond to seismic signals, the processes of toppling and sliding present column- and V-shaped spectrograms, respectively. The impacts of rockfall link directly to the pulses of seismic signals. Here, all spectrogram features of events can be identified for events with volumes larger than 2000 m3, corresponding to the farthest epicenter distance of ∼ 2.5 km. These results were obtained using the GeoLoc scheme for providing the government with rapid reports for reference. Finally, a recent event on 12 June 2020 was used to examine the GeoLoc scheme's feasibility. We estimated the event's volume using two scalings: 3838 and 3019 m3. These values were roughly consistent with the volume estimation of 5142 m3 from the digital elevation model. The physical processes, including rockfall, toppling, and complex motion behaviors of rock interacting with slope inferred from the spectrogram features were comprehensively supported by the video record and field investigation. We also demonstrated that the GeoLoc scheme, which has been implemented in Sinwulyu catchment, Taiwan, can provide fast reports, including the location, volume, and physical process of events, to the public soon after they occur.

scholarly journals Forecasting dam height and stability of dams formed by rock slope failures in Norway

2020 ◽  
Author(s):  
Thierry Oppikofer ◽  
Reginald L. Hermanns ◽  
Vegard U. Jakobsen ◽  
Martina Böhme ◽  
Pierrick Nicolet ◽  
...  
Keyword(s):  
Linear Relationship ◽  
Rock Slope ◽  
Landslide Dam ◽  
Power Laws ◽  
Dam Failure ◽  
Validation Dataset ◽  
Slope Failures ◽  
Empirical Relationships ◽  
The Stability ◽  
Semi Empirical

Abstract. Based on an inventory of 69 dams formed by rock slope failures in southwestern Norway and published landslide dam inventories from other parts of the World we developed semi-empirical relationships linking the maximum dam height (HD.max in m) to dam volume (VD in 106 m3) and other relevant parameters such as valley width (WV in m) or dam area (AD in km2). Power-laws are obtained for HD.max = f(VD) and HD.max = f(VD, WV), while a linear relationship links HD.max to the ratio VD / AD. For dams in southwestern Norway, the linear relationship HD.max = 1.75 × VD / AD has least uncertainties and provides best results when comparing predicted dam heights with a validation dataset composed of existing dams in northern Norway and numerically modelled dams for possible rock slope failures. To assess the stability of future dams we use the predicted dam heights in the dimensionless blockage index DBI and relating this index to the probability of dam failure derived from our dataset and other published databases on landslide dams. This study underlines the potential of semi-empirical relationships for assessing dam height and stability that needs to be included in preliminary hazard and risk assessment for unstable rock slopes, because damming of a river is an important secondary effect of landslides due to upstream flooding and possible outburst floods in case of dam failure.

scholarly journals Analytical technique for stability analyses of the rock slope subjected to slide head toppling failure mechanisms considering groundwater and stabilization effects

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Victor Mwango Bowa ◽  
Wenping Gong
Keyword(s):  
Analytical Solutions ◽  
Rock Slope ◽  
Failure Mechanisms ◽  
Jointed Rock ◽  
Shear Forces ◽  
Stability Analyses ◽  
Study Results ◽  
Toppling Failure ◽  
The Stability ◽  
Jointed Rock Slope

AbstractThe contributions of the current analytical models on the prediction of the stability of the slope subjected to slide head toppling failure mechanisms, have always focused on the idealized geometry comprising regular blocks dipping into the slope face. Besides, the influence of groundwater and stabilizations from the lowermost block of the slope have been overlooked in the available literature. In this article, the analytical solutions that incorporates the kinematic mechanisms of the jointed rock slope under the influence of groundwater and stabilizing the lowermost block subjected to slide head toppling are derived based on the limit equilibrium. Furthermore, a real slide head toppling failure case history was studied to illustrate the effectiveness of the presented analytical solutions. The investigation results indicate that the presence of groundwater in the jointed rock slope, lowers the distributions of the normal and shear forces thereby inducing slide head toppling. Reinforcing the lowermost block of the slope, enhances the distributions of the normal and shear forces thus improving the stability of the jointed rock slope. The study results depict that the presented analytical solutions can provide an accurate and efficient stability analyses of the jointed rock slope subjected to slide head toppling failure mechanisms considering the presence of groundwater and stabilization effects.

scholarly journals Locating rock slope failures along highways and understanding their physical processes using seismic signals

2020 ◽  
Author(s):  
Jui-Ming Chang ◽  
Wei-An Chao ◽  
Hongey Chen ◽  
Yu-Ting Kuo ◽  
Che-Ming Yang
Keyword(s):  
Rock Slope ◽  
Scaling Law ◽  
Mass Movement ◽  
Hybrid Approach ◽  
Volume Estimation ◽  
Seismic Signals ◽  
Slope Failures ◽  
Physical Processes ◽  
Seismic Parameters ◽  
Duration Magnitude

Abstract. Regional monitoring of rock slope failures by the seismic technique is rarely studied due to significant source location errors, and it still lacks the signal features needed for understanding events of this type because of the complex mass movement involved. To better understand events of this type, ten known events along highways in Taiwan were analyzed. First, a hybrid approach (GeoLoc) composed of cross-correlation-based and amplitude-attenuation-based approaches was applied, and it produced a location error of maximum 3.19 km for the ten events. Then, we analyzed the ratio of local magnitude (ML) and duration magnitude (MD) and found that a threshold of 0.85 yields successful classification between rock slope failure and earthquake. Further, the GeoLoc can retrieve the seismic parameters, such as signal amplitude at the source (A0) and ML of events, which are crucial for constructing scaling law with source volume (V). Indeed, Log(V) = 1.12 ML + 3.08 and V = 77,290 A00.44 derived in this study provide the lower bound of volume estimation, since the seismic parameters based on peak amplitudes cannot represent the full process of mass loss. Second, while video records correspond with seismic signals, the processes of toppling and sliding present column- and V-shaped spectrograms, respectively. The impacts of rockfall directly link directly to the pulses of seismic signals. Here, all spectrogram features of events can be identified by event volumes larger than 2,000 m3, corresponding to the farthest epicenter distance ~2.5 km. The previous results were obtained using the GeoLoc scheme for providing the government rapid reports for reference. Finally, a recent event on 12th June 2020 was used to examine the GeoLoc scheme’s feasibility. We estimated the event's volume by the two scalings: 3,838 m3 and 3,019 m3, which was roughly consistent with the volume estimation of 5,142 m3 from the digital elevation model. The physical processes, including rockfall, toppling, and complex motion behaviors of rock interacting with slope inferred from the spectrogram features were comprehensively supported by the video record and field investigation. We also demonstrated that the GeoLoc scheme, which has been implemented in Sinwulu catchment, Taiwan, can provide fast reports, including the location, volume, and physical process of events of this type to the public soon after they occur.

scholarly journals Morphotectonics of mass movements on slopes

2000 ◽  
Vol 22 ◽  
Author(s):  
Adrian E. Scheidegger
Keyword(s):  
Stress Field ◽  
Principal Stress ◽  
Mass Movement ◽  
Mass Movements ◽  
Stress Directions ◽  
The Alps ◽  
The Stability ◽  
The Himalaya

The study describes the neotectonic effects on morphology of mass movements. Whilst the external (meteorological or seismic) processes are the immediate triggers of mass movements, their location and orientation is pre-designed by the tectonics of the area. The direction of mass movement is naturally in the direction down the slope of the valleys. If the latter are natural, they are parallel to the prevailing joints, which are shearing features of the neotectonic stress field. Most landslides, thus, are "shear" - or "wedge"-type failures. However, this is not true in the case of older valleys having been cause d e.g. by nappe-edges emplaced much before the present-day resulting in "mountain fractures" and "valley closures", and particularly by artificial cuts: in such cases, slides occur mainly on faces oriented at right angles to one of the principal neotectonic stress directions. Evidently, the stability of the object is reduced in this case and slides occur more frequently than if the valleys or cuts run parallel to such principal stress directions. These findings are illustrated by specific examples from the Himalaya and the Alps.

scholarly journals Semi-empirical prediction of dam height and stability of dams formed by rock slope failures in Norway

2020 ◽  
Vol 20 (11) ◽  
pp. 3179-3196
Author(s):  
Thierry Oppikofer ◽  
Reginald L. Hermanns ◽  
Vegard U. Jakobsen ◽  
Martina Böhme ◽  
Pierrick Nicolet ◽  
...  
Keyword(s):  
Linear Relationship ◽  
Rock Slope ◽  
Power Laws ◽  
Dam Failure ◽  
Validation Dataset ◽  
Slope Failures ◽  
Empirical Relationships ◽  
Empirical Prediction ◽  
The Stability ◽  
Semi Empirical

Abstract. Based on an inventory of 69 dams formed by rock slope failures in southwestern Norway and published inventories from other parts of the world, we developed semi-empirical relationships linking the maximum dam height (HD.max in metres) to dam volume (VD in 106 m3) and other relevant parameters such as valley width (WV in metres) or dam area (AD in square kilometres). Power laws are obtained for HD.max=f(VD) and HD.max=f(VD, WV), while a linear relationship links HD.max to the ratio VD∕AD. For dams in southwestern Norway, the linear relationship HD.max=1.75×VD/AD has the least uncertainties and provides the best results when comparing predicted dam heights with a validation dataset composed of existing dams in northern Norway and numerically modelled dams for possible rock slope failures. To assess the stability of future dams, we use the predicted dam heights in the dimensionless blockage index (DBI) and relating this index to the probability of dam failure derived from our dataset and other published databases on landslide dams. This study underlines the potential of semi-empirical relationships for assessing dam height and stability that needs to be included in preliminary hazard and risk assessment for unstable rock slopes, because damming of a river is an important secondary effect of landslides due to upstream flooding and possible outburst floods in the case of dam failure.

scholarly journals Stability Analysis of Jointed Rock Slope by Strength Reduction Technique considering Ubiquitous Joint Model

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Ruili Lu ◽  
Wei Wei ◽  
Kaiwei Shang ◽  
Xiangyang Jing
Keyword(s):  
Rock Slope ◽  
Reduction Method ◽  
Domain Size ◽  
Jointed Rock ◽  
Strength Reduction ◽  
Hydropower Station ◽  
Strength Reduction Method ◽  
Vertical Side ◽  
The Stability ◽  
Jointed Rock Slope

In order to study the failure mechanism and assess the stability of the inlet slope of the outlet structure of Lianghekou Hydropower station, the strength reduction method considering the ubiquitous joint model is proposed. Firstly, two-dimension numerical models are built to investigate the influence of the dilation angle of ubiquitous joints, mesh discretization, and solution domain size on the slope stability. It is found that the factor of safety is insensitive to the dilation angle of ubiquitous joints and the solution domain size but sensitive to the mesh discretization when the number of elements less than a certain threshold. Then, a complex three-dimension numerical model is built to assess the stability of the inlet slope of the outlet structure of Lianghekou Hydropower station. During the strength reduction procedure, the progressive failure process and the final failure surface of the slope are obtained. Furthermore, the comparison of factors of safety obtained from strength reduction method and analytical solutions indicates that the effect of vertical side boundaries plays an important role in the stability of jointed rock slope, and the cohesive force is the main contribution to the resistant force of vertical side boundaries.

Multistage Rock-Slope Failures Revealed in Lake Sediments in a Seismically Active Alpine Region (Lake Oeschinen, Switzerland)

2018 ◽  
Vol 123 (4) ◽  
pp. 658-677 ◽  
Author(s):  
Sibylle Knapp ◽  
Adrian Gilli ◽  
Flavio S. Anselmetti ◽  
Michael Krautblatter ◽  
Irka Hajdas
Keyword(s):  
Lake Sediments ◽  
Rock Slope ◽  
Alpine Region ◽  
Slope Failures

Recurrent rock avalanches progressively dismantle mountain ridges in the Longmen Shan, China, most recently in the 2008 Wenchuan earthquake

2021 ◽  
Author(s):  
Janusz Wasowski ◽  
Maurice McSaveney ◽  
Luca Pisanu ◽  
Vincenzo Del Gaudio ◽  
Yan Li ◽  
...  
Keyword(s):  
Wenchuan Earthquake ◽  
Ambient Noise ◽  
Slope Failure ◽  
Mass Movement ◽  
Rock Avalanche ◽  
Ground Vibration ◽  
Source Area ◽  
Slope Failures ◽  
Rock Avalanches ◽  
Beichuan County

<p>Large earthquake-triggered landslides, in particular rock avalanches, can have catastrophic consequences. However, the recognition of slopes prone to such failures remains difficult, because slope-specific seismic response depends on many factors including local topography, landforms, structure and internal geology. We address these issues by exploring the case of a rock avalanche of >3 million m<sup>3</sup> triggered by the 2008 Mw7.9 Wenchuan earthquake in the Longmen Shan range, China. The failure, denominated Yangjia gully rock avalanche, occurred in Beichuan County (Sichuan Province), one of the areas that suffered the highest shaking intensity and death toll caused by co-seismic landsliding. Even though the Wenchuan earthquake produced tens of large (volume >1 million m<sup>3</sup>) rock avalanches, few studies so far have examined the pre-2008 history of the failed slope or reported on the stratigraphic record of mass-movement deposits exposed along local river courses. The presented case of the Yangjia gully rock avalanche shows the importance of such attempts as they provide information on the recurrence of large slope failures and their associated hazards. Our effort stems from recognition, on 2005 satellite imagery, of topography and morphology indicative of a large, apparently pre-historic slope failure and the associated breached landslide dam, both features closely resembling the forms generated in the catastrophic 2008 earthquake. The follow-up reconstruction recognizes an earlier landslide deposit exhumed from beneath the 2008 Yangjia gully rock avalanche by fluvial erosion since May 2008. We infer a seismic trigger also for the pre-2008 rock avalanche based on the following circumstantial evidence: i) the same source area (valley-facing, terminal portion of a flat-topped, elongated mountain ridge) located within one and a half kilometer of the seismically active Beichuan fault; ii) significant directional amplification of ground vibration, sub-parallel to the failed slope direction, detected via ambient noise measurements on the ridge adjacent to the source area of the 2008 rock avalanche and iii) common depositional and textural features of the two landslide deposits. Then, we show how, through consideration of the broader geomorphic and seismo-tectonic contexts, one can gain insight into the spatial and temporal recurrence of catastrophic slope failures  in Beichuan County and elsewhere in the Longmen Shan. This insight, combined with local-scale geologic and geomorphologic knowledge, may guide selection of suspect slopes for reconnaissance, wide-area ambient noise investigation aimed at discriminating their relative susceptibility to co-seismic catastrophic failures. We indicate the feasibility of such investigations through the example of this study, which uses 3-component velocimeters designed to register low amplitude ground vibration.</p>

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