Intriguing. It is pretty randomized for a magnetic effect, though, if it were, that randomisation, that would mean then that the source was moving, and quite erratic. From the area covered (60 X 30 km), then it would have been quite a large anomaly that did the moving.
Could it be an underground lava flow?
Seanie?
Midlands Astronomy Club.
Radio Presenter (Midlands 103), Space Enthusiast, Astronomy Outreach Co-ordinator.
Former IFAS Chairperson and Secretary.
  