Abstract: A seismic pulse generator (1) has a chamber (4) pressurised with gas. The generator includes a solenoid valve (60) which can be actuated to cause the release to atmosphere of only a small amount of pressurised gas from a small control chamber (34) behind a main piston (30) to enable the piston to move away from a valve seat (32) around an outlet (26). This permits the abrupt release of the pressurised gas in the chamber (4) through the outlet and the “firing” of the generator. The arrangement maximises the use of the main pressurised gas for actual “firing” of the generator.

Abstract: The method involves using an acoustic wave generating apparatus, such as an "air gun", which employs only a single gas or single gas mixture and which has a gas pressurizable chamber with an inlet for permitting pressurized gas to be introduced into the chamber and a closed outlet which can be opened rapidly to release pressurized gas from the chamber into a liquid to generate acoustic wave energy. Hydrogen and/or helium is/are used instead of air as the gas with the result that the strength and quality of the initial pulse of the generated wave energy is improved.