The role of sediment composition and behavior under dynamic loading conditions on slope failure initiation: a study of a subaqueous landslide in earthquake-prone South-Central Chile

Abstract

Subaqueous slope failure mechanisms are still poorly understood partly because they are difficult to study due to the remote location of submarine landslides. Landslides in lakes are smaller in size and more readily accessible and therefore represent a good alternative to their marine counterparts. Lake Villarrica, located in South-Central Chile, experienced significant slope failure and serves here as an exemplary study area for subaqueous landslide initiation mechanisms in tectonically active settings. Coring and CPTU testing were undertaken with the MARUM free-fall CPTU deployed adjacent to the coring sites where all lithological units involved in the slope failure were sampled. Using geotechnical methods such as pseudo-static factor of safety analysis and cyclic triaxial testing, three types of soils (i.e., diatomaceous ooze, volcanic ash, and quick clay) were analyzed for their role in slope failure, and earthquake shaking was identified as the primary trigger mechanism. The investigated landslide consisted of two distinct phases. During the first phase, slope failure was initiated above a tephra layer. In the second phase, retrogression led to the shoreward extension of the slide scarp along a second failure plane located in a stratigraphically deeper, extremely sensitive lithology (i.e., quick clay). Results show that liquefaction of buried tephra layers was unlikely, but such layers might still have contributed to a reduction in shear strength along the contact area with the neighboring sediment. Furthermore, cyclic shaking-induced pore pressure in diatomaceous ooze may be similar to that in granular soils. We generally infer that failure mechanisms observed in this study are equally important for landslide initiation in submarine settings as diatomaceous ooze intercalated with volcanic ash may be abundantly present along active continental margins

Soft sediment deformation in the shallow submarine slope off Nice (France) as a result of a variably charged Pliocene aquifer and mass wasting processes

“…During the testing procedure axial strain, vertical load (σ n ), cell pressure (σ c ) and pore water pressure were monitored and recorded (for more detail see Wiemer et al, 2015).…”

“…The cylindrical specimens had a circular area of 0.001 m 2 and a height of 75 mm ± 3 mm. The specimens were assembled in a Stenzel triaxial cell (for technical details refer to Wiemer et al (2015)). …”

A multi-centennial record of past floods and earthquakes in Valle d'Aosta, Mediterranean Italian Alps

“…This high sensitivity of Lago Inferiore to earthquake shaking may be explained by many factors like slope angle, sediment thickness or geotechnical properties of the sedimentary succession (e.g. Morgenstern, 1967;Strasser et al, 2011;Ai et al, 2014;Wiemer et al, 2015). However, Wilhelm et al (2016b) suggested that the dominant factor explaining the lake sensitivity of such Alpine lakes is the sedimentation rate, i.e.…”

Altered marine tephra deposits as potential slope failure planes?

“…Fresh volcanic fall-out ashes have been suggested or identified as glide planes of submarine landslides (e.g. Harders et al 2010;Expedition 340 Scientists 2012;Sassa et al 2012;Strasser et al 2012;Laberg et al 2014;Wiemer et al 2015), where earthquaketriggered liquefaction (Castro 1975) was argued to be the most likely sediment failure mechanism. The submarine landslide community currently debates on whether fresh volcanic fallout ash may act as 'induced weak layer' as defined in Locat et al (2014).…”