A seismic generation system may include an electrical source, a conductor coupled to the electrical source and to be positioned in a wellbore in a subterranean formation with a casing therein, and a seismic generation source assembly to be positioned in the wellbore and coupled to the conductor. The seismic generation source assembly may include a source element having a sealed housing, an armature within the sealed housing, source electromagnets coupled to the armature, and electromagnetic clamps coupled to the armature, each electromagnetic clamp having opposite magnetic poles. The sealed housing may include respective ferromagnetic portions adjacent the opposite magnetic poles of each electromagnetic clamp, and non-ferromagnetic portions between the opposite magnetic poles of each electromagnetic clamp.