The invention provides methods and apparatus for detecting seismic waves propagating
through a subterranean formation surrounding a borehole. In a first embodiment,
a sensor module uses the rotation of bogey wheels to extend and retract a sensor
package for selective contact and magnetic coupling to casing lining the borehole.
In a second embodiment, a sensor module is magnetically coupled to the casing wall
during its travel and dragged therealong while maintaining contact therewith. In
a third embodiment, a sensor module is interfaced with the borehole environment
to detect seismic waves using coupling through liquid in the borehole. Two or more
of the above embodiments may be combined within a single sensor array to provide
a resulting seismic survey combining the optimum of the outputs of each embodiment
into a single data set.