Electroacoustic pulse source for high resolution seismic prospectings

A seismic source adapted for high resolution seismic prospecting comprising:

• an electroacoustic transducer including a metallic hollow bell-shaped structure having a closed head and an open base that is closed by an elastic diaphragm, and being filled with a dielectric liquid, the structure having an inner reflective surface in the shape of a circular paraboloid having a vertical axis and a focal point, the structure further enclosing a pair of main electrodes positioned near the head on opposite sides of the focal point and with a gap therebetween, an auxiliary electrode positioned in the gap between the two main electrodes, and means for moving the main and auxiliary electrodes vertically along the vertical axis to vary their distance from the focal point and for moving the main electrodes horizontally normal to the axis to vary the width of the gap;
• first circuit means for storing energy in a capacitor bank for maintaining a voltage across the main electrodes insufficient for initiating a discharge across the gap so long as the dielectric liquid in the gap is not ionized, and;
• second circuit means connected between one of the main electrodes and the auxiliary electrode for establishing therebetween controllably a voltage sufficient to ionize the dielectric liquid in the gap whereby there is triggered an electrical discharge between the two main electrodes across the gap for exciting an acoustic wave in the dielectric liquid directed at the elastic diaphragm at the base end of the hollow structure.