An experimental, laboratory sand model study of the origin of a decompression zone due to fluid extraction in a rock mass was carried out. It was found that an arch structure of sand density changes was formed above the decompression zone. The arch structure, which bears a portion of the load of the upper layer of the sand, can be destroyed by the action of seismic waves. The destruction of the arch causes an increase in fluid pressure in the decompressed zone. The value of the pressure increase is directly proportional to the depth of the decompression zone and inversely proportional to the dimension of the zone.