Displaceable diaphragm structures for use in seismic impulse transmission

Claim 1

A seismic energy source for surveying on the earth by transmitting seismic energy impulses into the earth and being of the type having a closed dome-shaped tank with a igid curved side and top wall containing a substantilly incompressible liquid with at least one air gun for abruptly releasing pressurized gas into the liquid in the dome-shaped tank, wherein the invention comprises independently movable apparatus coupling the tank to the earth for transmitting powerful seismic impulses into the earth including a tank flange extending outwardly around the lower rim of the dome-shaped tank, a resilient flexible diaphragm of tough flexible material such as polyurethane extending across the bottom of said tank, the perimeter of said diaphragm being clamped to said tank flange for sealing the incompressible liquid within the tank, an outer freely movable cylinder surrounding the tank and extending upwardly around the tank, said outer movable cylinder being spaced outwardly from the periphery of the tank with the tank being freely movable upwardly for a distance with respect to said movable cylinder from a first lower rest position, to a second elevated position spaced from the lower rest position, a metal diaphragm plate extending across under the bottom of the tank beneath said resilient flexible diaphragm, said metal diaphragm plate being adapted to rest down upon the earth and having its perimeter secured to the bottom of said movable cylinder to form therewith a cup-shaped structure in which said tank rests and having a diameter larger than said tank with said movable cylinder being spaced outwardly beyond the periphery of the tank and surrounding the tank for distributing the weight of the seismic source on the earth over a metal diaphragm plate larger than the diameter of the seismic source, whereby upon firing of the air gun to abruptly release pressurized gas into the liquid, the flexible resilient diaphragm and the metal diaphragm plate can be displaced freely downwardly and the tank can rise freely within said outer cylinder between said rest and elevated positions, thereby maintaining said metal diaphragm plate in contact with the earth as the tank rises, for transmitting a powerful seismic impulse into the earth.