Abstract: Arrangement for use for seismic surveys of geological formations in a seabed, where a plurality of such arrangements, which are provided with sensor units 26, are placed on the seabed for collecting pressure waves and shear waves reflected from the geological formations. There exist arrangements for transferring seismic data to a surface receiver placed on a vessel, an offshore installation, or an onshore installation. Each sensor unit 26 is held by a carrier 10 and is connected to a cylindrically skirt-shaped structure 19 adapted to be led down into the seabed, and each sensor unit 26 comprises at least one geophone. The carrier 10 comprises a holder 12 for the cylindrically skirt-shaped structure 19, which structure 19 shall penetrate down into the seabed, as this holder 12 is adapted to be moved between a lower position and an upper position, to be able to be mechanically released from the skirt-shaped structure 19.