The British Caving Association

Here is a reference using 70-100 Hz to image a oil field at a depth of 3000' and the reflection of layers at 12,000' were measured all with frequencies higher than 40 Hz. See pages 55-58 in the following reference: https://www.slb.com/~/media/Files/resources/oilfield_review/ors95/aut95/08955260.pdf ...

i just checked a page on sea floor mapping. The lowest frequency used for a ship towed array is 50 Hz. At that frequency depth penetration is in excess of 10,000 feet so in practical terms where the receiver is at depth rather than detecting a reflection, the depth penetration could easily be 10,000...

A thought on a signal source, perhaps a electric solenoid could be used as a tapper controlled by the computer. There are many auto solenoids that could be used or you could roll your own. This might be a interesting approach fot generating a signal.

Best Regards

Jim

The attenuation at seismic frequencies is quite low. The reflections from a 20,000 foot deep reflector are detected by a seismic sensor at the surface- so the signal had to transit 40,000 feet of rock to both get to 20,000 feet and then the weak reflection then returns to the surface. So, At seismic...

Dear sirs: I am a geologist and subscriber to the creg journal residing in the United States, and I have some thoughts on underground communication for your group that I would like to present. Cave communications have focused on radio which does indeed penetrate rocks however there is a alternative ...