GB1412399A - Apparatus for and methods of seismic prospecting - Google Patents

Abstract

1412399 Seismic exploration systems ELECTROLOCATION Ltd 1 Dec 1972 [4 Dec 1971] 56387/71 Heading H4D A seismic exploration method comprises recording signals corresponding to a generated seismic pulse and the subterranean reflection response in first and second channels respectively, using the played back pulse signal to initiate re-recording of the reflection signal and recording of a tone burst in continuation of the second and first channels respectively, and making visual tracings of the played back rerecorded signal over the duration of the recorded tone burst. In the Fig. 3, embodiment a rod 17, attached to a hammer used as the seismic source, operates switch 16 to turn on tape recorder 19 just before the hammer head impacts the ground, so that the tape runs up to its correct speed (7 in./sec.) before recording of resulting reflection signals starts. The impact instant is recorded as a pulse in a first channel by use of a transducer on the hammer. Reflection signals from a geophone are recorded in a second channel. The tape is then played back and the pulse in the first channel is used to initiate (a) recording of a tone burst, from oscillator 30, in a first channel of recorder 25 and (b) re-recording of the second channel signals in a second channel of recorder 25. Played back second channel signals from recorder 25 are obtained as pulses by including Schmitt and differentiator circuits at either 24a or 35. These pulses are traced by a digital plotter 32, the playback and plotting being synchronized by the recorded tone burst. The playback speeds of recorders 24 and 25 may be lower (e.g. 15/16 in./sec.) than the recording speeds to expand the time scale of the signals. The geophone may be short-circuited or electromagnetically damped at the impact instant to avoid signal distortions.