A database of potential paleoseismic evidence in Switzerland

Kremer, Katrina; Gassner-Stamm, Gabriela; Grolimund, Remo; Wirth, Stefanie B.; Strasser, Michael; Fäh, Donat

doi:10.1007/s10950-020-09908-5

Cited by 21 publications

(31 citation statements)

References 61 publications

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“…This earthquake (EQ-8) falls into a period of Alpine-wide enhanced seismicity between 9.5 – 9.9 ka BP during which some of the largest rockslides in the Alps took place (e.g. Flims, Köfels) 42 .…”

Section: Resultsmentioning

confidence: 99%

Seismic control of large prehistoric rockslides in the Eastern Alps

et al. 2021

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Large prehistoric rockslides tend to occur within spatio-temporal clusters suggesting a common trigger such as earthquake shaking or enhanced wet periods. Yet, trigger assessment remains equivocal due to the lack of conclusive observational evidence. Here, we use high-resolution lacustrine paleoseismology to evaluate the relation between past seismicity and a spatio-temporal cluster of large prehistoric rockslides in the Eastern Alps. Temporal and spatial coincidence of paleoseismic evidence with multiple rockslides at ~4.1 and ~3.0 ka BP reveals that severe earthquakes (local magnitude ML 5.5–6.5; epicentral intensity I0 VIII¼–X¾) have triggered these rockslides. A series of preceding severe earthquakes is likely to have progressively weakened these rock slopes towards critical state. These findings elucidate the role of seismicity in preparing and triggering large prehistoric rockslides in the European Alps, where rockslides and earthquakes typically occur in clusters. Such integration of multiple datasets in other formerly glaciated regions with low to moderate seismicity will improve our understanding of catastrophic rockslide drivers.

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Section: Resultsmentioning

confidence: 99%

Seismic control of large prehistoric rockslides in the Eastern Alps

et al. 2021

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“…The age of the Köfels rockslide was determined several times through radiocarbon dating of wood buried by the rockslide deposits , surface exposure dating of rockslide boulders (Kubik et al, 1998) and actually by treering analysis and radiocarbon dating of new wood samples (Nicolussi et al, 2015). The last dating campaign, yielding 9527-9498 cal BP, led to a significant refining of the timing of the Köfels landslide event and even was able to constrain the season during which the event occurred.…”

Section: The Köfels Rockslidementioning

confidence: 99%

Geographic-information-system-based topographic reconstruction and geomechanical modelling of the Köfels rockslide

Zangerl

Schneeberger

Steiner

et al. 2021

Nat. Hazards Earth Syst. Sci.

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Abstract. The Köfels rockslide in the Ötztal Valley (Tyrol, Austria) represents the largest known extremely rapid landslide in metamorphic rock masses in the Alps. Although many hypotheses for the trigger were discussed in the past, until now no scientifically proven trigger factor has been identified. This study provides new data about the (i) pre-failure and failure topography, (ii) failure volume and porosity of the sliding mass, and (iii) numerical models on initial deformation and failure mechanism, as well as shear strength properties of the basal shear zone obtained by back-calculations. Geographic information system (GIS) methods were used to reconstruct the slope topographies before, during and after the event. Comparing the resulting digital terrain models leads to volume estimates of the failure and deposition masses of 3100 and 4000 million m3, respectively, and a sliding mass porosity of 26 %. For the 2D numerical investigation the distinct element method was applied to study the geomechanical characteristics of the initial failure process (i.e. model runs without a basal shear zone) and to determine the shear strength properties of the reconstructed basal shear zone. Based on numerous model runs by varying the block and joint input parameters, the failure process of the rock slope could be plausibly reconstructed; however, the exact geometry of the rockslide, especially in view of thickness, could not be fully reproduced. Our results suggest that both failure of rock blocks and shearing along dipping joints moderately to the east were responsible for the formation or the rockslide. The progressive failure process may have taken place by fracturing and loosening of the rock mass, advancing from shallow to deep-seated zones, especially by the development of internal shear zones, as well as localized domains of increased block failure. The simulations further highlighted the importance of considering the dominant structural features of the rock mass. Considering back-calculations of the strength properties, i.e. the friction angle of the basal shear zone, the results indicated that under no groundwater flow conditions, an exceptionally low friction angle of 21 to 24∘ or below is required to promote failure, depending on how much internal shearing of the sliding mass is allowed. Model runs considering groundwater flow resulted in approximately 6∘ higher back-calculated critical friction angles ranging from 27 to 30∘. Such low friction angles of the basal failure zone are unexpected from a rock mechanical perspective for this strong rock, and groundwater flow, even if high water pressures are assumed, may not be able to trigger this rockslide. In addition, the rock mass properties needed to induce failure in the model runs if no basal shear zone was implemented are significantly lower than those which would be obtained by classical rock mechanical considerations. Additional conditioning and triggering factors such as the impact of earthquakes acting as precursors for progressive rock mass weakening may have been involved in causing this gigantic rockslide.

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“…Many rock avalanches have filled valleys and created landslide dammed lakes, and these catastrophic events can be a significant hazard to people and infrastructure located in the potential runout zone (Schwinner, 1912;Heim, 1932;Abele, 1974;Hovius et al, 1997;Korup and Tweed, 2007;Fort et al, 2009;Loew et al, 2017). Detailed studies of pre-historic landslides are important to understand the risk posed by these natural hazards, and understand post-glacial slope dynamics, landscape evolution, and paleoseismicity (Hovius et al, 1997;Hungr et al, 1999;Korup and Clague, 2009;Huggel et al, 2013;Grämiger et al, 2016;Ivy-Ochs et al, 2017a;Kremer et al, 2020;Singeisen et al, 2020). This requires knowledge of the volume, source area location and runout characteristics of these events, and inaccurate interpretations of these features can lead to misleading conclusions regarding rock avalanche hazard and mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Constraining the Age and Source Area of the Molveno landslide Deposits in the Brenta Group, Trentino Dolomites (Italy)

et al. 2020

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Rock avalanches are low frequency natural hazards that can alter landscape morphology, and constraining the timing, volume and emplacement dynamics of prehistoric rock avalanches is crucial for understanding the hazards posed by these events. Here we perform cosmogenic nuclide dating, topographic reconstruction and runout modeling of the Molveno rock avalanche, located north of Lake Garda in the Province of Trento, Italy. The unique morphology of the deposits, which features numerous large scarps and prominent lineaments, have previously led researchers to interpret the Molveno rock avalanche as being the result of multiple events. Our results show that the Molveno rock avalanche had a volume of approximately 600 Mm 3 , and failed from a prominent niche located on Monte Soran. 36 Cl cosmogenic nuclide dating results shows that the deposits were emplaced as a single event approximately 4.8 ± 0.5 ka, and suggests that the unique deposit morphology is due to the emplacement processes acting during and soon after failure. Numerical runout modeling shows that this morphology could have resulted from a combination of runup and extensional spreading of the debris along the complex valley floor topography. The ages we determined for this event are coincident with the nearby Marocca Principale rock avalanche (5.3 ± 0.9 ka), which may suggest a common trigger. Our results have important implications for interpreting the morphology of rock avalanche deposits, and contribute to the evolving understanding of rock avalanche processes in the Alps.

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A database of potential paleoseismic evidence in Switzerland

Cited by 21 publications

References 61 publications

Seismic control of large prehistoric rockslides in the Eastern Alps

Seismic control of large prehistoric rockslides in the Eastern Alps

Geographic-information-system-based topographic reconstruction and geomechanical modelling of the Köfels rockslide

Constraining the Age and Source Area of the Molveno landslide Deposits in the Brenta Group, Trentino Dolomites (Italy)

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