“Shaken not stirred”: Mosaic sand – a semi-liquefaction phenomenon originating from strong earthquakes
The formation of mosaic sand, here as exemplified from a 0.23 km2 sand field at the coast of Nordland County in Northern Norway, is thought to be related to earthquake induced shaking, re-mobilization and partial (semi-) liquefaction of water-saturated, stratified fine and medium sand. It is therefore a part of the broad class of sediments with seismically induced deformations, known as seismites. The process associated with the formation of mosaic sand may best be described as 'shaken, not stirred', because the individual parts of stratified sands are apparently not totally removed from their original position. The layers are rather broken, fragmented in pieces or ball-like structures, which are deformed, partly rotated and then settled in a complex mosaic mixture. It may also appear just as a cluster of load casts. The structure developed resembles those of a dense conglomerate, a cluster of pseudo-nodules, or as pudding balls (armored sediment balls) cemented by sand.