It has long been known that fault initiation, propagation and slip are a function of fault zone mineralogy and transient pore pressure [Hubbert and Rubey, 1959]. Separating the effect of intrinsic sediment friction from that of pore pressure is one of the major targets in marine soil mechanics. Attempts to achieve this goal usually rely on modelling or estimating the excess pore pressure from geophysical data or water release due to mineral dehydration and gas hydrate processes [Moore and Shipboard Party ODP Leg 156, 1995; Brown et al., 2001; Saffer et al., 2000]. However, these studies do not include the in situ measurement of pore pressure and are hence hampered by uncertainties. In our study of Lake Lucerne slope deposits, we are able to separate the two factors by a suite of in situ and laboratory measurements. On a regional level, our results show a reliable quantitative geotechnical characterization of the undisturbed glacial-to-postglacial succession in the source area of the Weggis Slide, which failed along a planar sliding surface that developed at the lithological boundary between slightly underconsolidated postglacial deposits and overconsolidated glacial deposits. Measured in situ pore pressure can be related to the different states of consolidation (see Figures 1, 2c, and S1), where negative insertion pore pressure in the overconsolidated unit may be generated by dilatant shear behavior with a displacement of fluids during insertion and a following slow increase of pore pressure controlled by the low permeability. We can exclude, that measured negative response is due to suction by pulling back the tool, because the acceleration sensor did not show any movement after insertion. Undrained shear strength, measured and derived with several methods, accentuates the difference in strength and consolidation state between the two lithologies. In contrast, laboratory ring shear frictional properties reveal no significant difference in the mechanical behavior of glacial and postglacial sediments. We conclude that pore pressure (and related lowering of effective stress) rather than the presence of weak mineral phases plays the key role in failure initiation along the Weggis slope. On a broader scale, our results may have important repercussions for triggering of failure processes along marine slopes and continental margins at lowered effective stresses. We condense our result to a model of earthquake-triggered failure initiation along the lithological boundary between two sediment layers with similar intrinsic mechanical behavior, but different consolidation and pore pressure regimes. The underlying overconsolidated sediments have lower permeability and higher shear strength, while their overburden drape is characterized by slightly more permeable, less competent sediments (Figure 4). At constant stress, such a slope is stable (Figure 4a). In case of an earthquake, however, seismic pulses from the poroelastic response to the earthquake-induced strain generate hydrological transients and - possibly - hydrofractures [Cocco and Rice, 2002]. A stress pulse may disrupt the overconsolidated glacial clay, thereby transferring excess pore fluid pressures up to less stable Holocene deposits (Figure 4b). This model may be transferred from the micro-scale lacustrine realm to the macro-scale landslide prone active and passive margins. Long-term records of pore pressure along the Nankai Trough [Davis et al., 2006] and Costa Rica subduction zones [Brown et al., 2005] and of water-level oscillations on-shore Oregon [Brodsky et al., 2003] have documented the interaction between seismicity and pore pressure as well as its transfusion over tens of kilometres. At the frontal thrust of the Nankai accretionary prism, Davis et al.  have measured up to >100 kPa increase in pore pressure to low-frequency EQs (M3.5–4.4) some 10 s of km away. Given that the 1601 A.D. M 6.2 EQ epicenter is only 15 km from the Weggis site, even a smaller pore pressure pulse may likely have caused values in excess of lithostatic (see arrows in Figure 4c). Hydrofracturing may have been facilitated by the historically documented 4 m-high tsunami waves after the 1601 EQ, which caused cyclic normal stress drops and eventually failure. This mechanism seems similar to large-scale landslides in seismic and/or tectonically active regions, where transient pore pressure pulses as main triggers have been proposed. One of the largest landslides is the Storegga Slide on the Mid-Norwegian shelf (3000 km3). Considering the pre-failure condition for slope instability (rapid loading of clayey sediments, over-pressuring during glaciation cycles and possible dissociation of gas hydrates) initial failure has been linked to a M > ∼7 EQ [Bryn et al., 2005]. Other large mass movements at passive margins are often related to rapid sediment accumulation and overpressures (New Jersey margin; Dugan and Flemings ). Slope failure along convergent margins may be associated with tectonic steepening and fluid venting during subduction processes (e.g., slumps and landslides along the Middle American Trench; von Huene et al. ). At volcanic margins or islands, both seismicity in the magma chamber and hydrothermal circulation adjacent to it influence the pore pressure regime, making these factors responsible for mega-landslides such as those in La Palma, Canary Island (ca. 5000 km2; Masson et al. ) or the Nuuanu Landslide, Hawaiian Islands (ca. 5000 km2; Moore et al. ).