Recognising surface versus sub-surface deformation of soft-sediments: Consequences and considerations for palaeoseismic studies

Soft-sediment deformation structures associated with slumps and mass transport deposits (MTDs) are generally considered to form at the surface when unlithified sediment moves downslope under influence of gravity. Where stratigraphic sequences contain several deformed horizons, question arises as whether repeated slope failure has systematically built-up multiple MTDs in record a ‘sequential model’. Alternatively, single event may concurrently create surficial sub-surface ‘intrastratal’ horizons different levels ‘synchronous The implications these differing models important can be significantly younger than depositional age beds it affects thereby weakening age-depth correlations used estimate timing palaeo-earthquakes. In order investigate potential for deformation, we examine late Pleistocene Lisan Formation exposed around Dead Sea Basin that contains numerous gravity-driven fold thrust systems. Surficial is recognised by identifying irregular erosive surfaces above overlain sedimentary caps deposited out suspension following event. Such also characterised thickened successions ‘growth’ sequences. Conversely, intrastratal typified detachment-bound folds thrusts marked repetitions stratigraphy across upper detachment surface, fluidised intrudes upwards into overlying sequence, together abrupt truncations older faults developed overburden detachment. created relatively competent subsequently buried they internally disrupted lack ‘layer-cake’ geometries, while seismicity lead dewatering compaction resulting ‘seismic strengthening’. Later therefore focussed adjacent earlier mechanical stratigraphy, leading secondary failures complications attempting ‘balance’ extension contraction ages. Sub-surface localised along discrete detachments carry sequence intact slides, affecting what appear ‘undeformed’ between individual MTDs. As does not directly correlate caps, rates movement on deeper remain unconstrained slower creep pile. • We catalogue establish key criteria help distinguish versus soft-sediments (SSD). Sequential model involves seismogenic builds-up SSDs record. Synchronous seismic creates concurrent levels. Secondary SSD influencing location later overprinting relationships. recognition during weakens palaeoseismic analysis.