Repetitive Late Pleistocene soft‐sediment deformation by seismicity‐induced liquefaction in north‐western Lithuania

Liquefaction can cause deformation of unconsolidated sediment, but specificprocesses involved and the trigger mechanisms often remain obscured. Thisstudy describes multiple deformed sediment layers in a succession of lacus-trine sand, silt and clay deposited during the Marine Isotope Stage 5d innorth-western Lithuania. The deformation structures (load casts, pseudonod-ules, ball-and-pillow structures, broken-up laminae and injections) are embed-ded in ten separate layers of fine-grained, laterally continuous sediments.Detailed mesoscale sedimentological analyses suggest that each deformationevent consisted of numerous successive stages of sediment advection facili-tated by liquefaction. Low-permeability fine-grained laminae contributed tolocalized pore-water pressure build-up and lowering of sediment strength.Erosional top surfaces that truncate layers with soft-sediment deformationstructures suggest that at least seven deformation events were separated bysuccessive periods of initial erosion and then uninterrupted deposition in thelake. The most likely trigger of the deformation was recurrent palaeoseismicactivity possibly linked to a late glacial isostatic adjustment following theScandinavian Ice Sheet melting after the Saalian glaciation. This study empha-sizes the potential role of seismic processes in shaping the sedimentary recordof the intraplate region of north-eastern Europe and contributes to constrainingthe depth of liquefaction, regardless of the actual trigger mechanism.