A marine vibrator , comprising: a support frame ; an auxiliary tank coupled to the support frame; and a plurality of pistons coupled to the support frame and adapted to receive a gas from the auxiliary tank , characterised in that each piston comprises: an actuated head ; and an actuation mechanism adapted to move the actuated head, the actuation mechanism comprising: at least one pair of cam assemblies, wherein each cam assembly comprises: a shaft ; and a plurality of cams coupled to the shaft, wherein each cam is coupled to the shaft at a location displaced from the center of the cam; a motor coupled to the shaft of each cam assembly; and a vacuum piston coupled to each pair of cam assemblies by two transfer members , wherein each transfer member is coupled between the actuated head and the vacuum piston such that the transfer member contacts the outer surface of a cam of the pair of cam assemblies, wherein synchronous use of the vacuum piston and the motors is adapted to stroke the piston . a support frame ; an auxiliary tank coupled to the support frame; and a plurality of pistons coupled to the support frame and adapted to receive a gas from the auxiliary tank , characterised in that each piston comprises: an actuated head ; and an actuation mechanism adapted to move the actuated head, the actuation mechanism comprising: at least one pair of cam assemblies, wherein each cam assembly comprises: a shaft ; and a plurality of cams coupled to the shaft, wherein each cam is coupled to the shaft at a location displaced from the center of the cam; a motor coupled to the shaft of each cam assembly; and a vacuum piston coupled to each pair of cam assemblies by two transfer members , wherein each transfer member is coupled between the actuated head and the vacuum piston such that the transfer member contacts the outer surface of a cam of the pair of cam assemblies, wherein synchronous use of the vacuum piston and the motors is adapted to stroke the piston . an actuated head ; and an actuation mechanism adapted to move the actuated head, the actuation mechanism comprising: at least one pair of cam assemblies, wherein each cam assembly comprises: a shaft ; and a plurality of cams coupled to the shaft, wherein each cam is coupled to the shaft at a location displaced from the center of the cam; a motor coupled to the shaft of each cam assembly; and a vacuum piston coupled to each pair of cam assemblies by two transfer members , wherein each transfer member is coupled between the actuated head and the vacuum piston such that the transfer member contacts the outer surface of a cam of the pair of cam assemblies, wherein synchronous use of the vacuum piston and the motors is adapted to stroke the piston . at least one pair of cam assemblies, wherein each cam assembly comprises: a shaft ; and a plurality of cams coupled to the shaft, wherein each cam is coupled to the shaft at a location displaced from the center of the cam; a shaft ; and a plurality of cams coupled to the shaft, wherein each cam is coupled to the shaft at a location displaced from the center of the cam; a motor coupled to the shaft of each cam assembly; and a vacuum piston coupled to each pair of cam assemblies by two transfer members , wherein each transfer member is coupled between the actuated head and the vacuum piston such that the transfer member contacts the outer surface of a cam of the pair of cam assemblies, wherein synchronous use of the vacuum piston and the motors is adapted to stroke the piston . <EOS>