Body face
- seismic reflector roughly parallel to the seafloor, a few hundred metres below it, cutting across sediment layers
- marks the base of the gas hydrate (clathrate) stability zone: hydrate-bearing sediment above, free gas below
- sharp drop in sound speed across it → reflection with reversed polarity relative to the seafloor
- depth set by pressure and temperature → estimate of the geothermal gradient without drilling
- moves when bottom water warms or sea level falls → hydrate dissociation, possible slope failure