Subsidence is the lowering of the Earth's surface due to aquifer-system compaction, drainage of organic soils, underground mining, primary and secondary compaction, hydrocompaction, etc., which occur below the upper sediments. It is therefore assumed that subsidence does not affect the dry bulk density of the upper sediments and only modifies the elevation of the bed surface and layers. The change in elevation due to subsidence is specified as user-defined subsidence rate (i.e. velocity).