There was discussions before regarding existence of an underground frozen ocean under mantle deep at 1200 – 1400 km, but now because of analysis equipments improvements, researches brings new concrete proves about existence of an giant underground water reservoir.
The results have been obtain from 80.000 analysis from 600.000 seismographs.
The underground ocean is under Asia and it is an ocean with cold water. The discovery could be done due to slowing down the speed of waves into water.
This might be the principal cause for frequently tectonics movements and modifications of continents.