An apparatus for generating a seismic signal in a wellbore includes an
elongated housing configured to be disposed in the wellbore; a piston
slidably disposed in an internal bore in the elongated housing; a strike
plate fixed on the elongated housing proximate one end of the internal
bore; and an energizing mechanism configured to move the piston to hit
the strike plate. A downhole system for seismic survey of a formation
penetrated by a wellbore includes at least one seismic receiver; a
seismic source; and at least one inflatable packer configured to separate
the seismic source and the at least one seismic receiver in different
compartments in the wellbore when inflated.