Compact seismic source for low frequency, humming seismic acquisition

A compact seismic source for seismic acquisition generating a humming signal includes a casing and a low-frequency reciprocating drive. The casing defines a fluid tight chamber and comprises a first casing section and a second casing section of roughly equal mass. The drive is disposed within the fluid tight chamber and, in operation, reinforces the natural reciprocating oscillation of the first and second casing sections relative to one another at a low seismic frequency. In one aspect, this action omni-directionally radiates the low frequency, humming seismic signal. On another aspect, the compact seismic source is substantially smaller than the wavelength of the low seismic frequency. Such a compact source may be deployed to omni-directionally radiate a low frequency, humming seismic signal during a seismic survey.