The ELF waves for pre-EQ stress are VERY long. This is why folks working on ELF have to bury miles of antenna wire. Ben Parks found another method, but it is proprietary and I am not privy.
I did think though...that certain good conductors of electricty might also be good antenna for sending waves over a long distance.. For instance railroad tracks....It is an area that I studied for a while...but could find no professional interest to keep me going...Andy Michaels thought I was barking up the wrong tree. Dr. Jon Dobson thought is possible but it was not in his research ballpark...just some thoughts as to what could act as antenna over a long distance?!