To detect VLF amateur signals it is pretty essential to use a good receiver (with frequency locking so extremely narrow bandwidths can be received for hours or days on end) and Spectrum Laboratory software. Spectrum Lab has options to lock to one of the powerful MSK signals near 20kHz and this transforms stability.
For reception of natural VLF emissions it is somewhat different as signals tend to be stronger and of much shorter duration. There are several VLF natural receivers on the net. See http://www.vlf.it/romero2/explorer-e202.html for a typical example.