Magnetic Field Reversal

[Robert Darwent]

if a large EMP were to occur by whatever means the I would guess that anything underground would be progressivly protected the further and deeper down it was situated so from the EMP

If the EMP was created from an airburst by a nuclear missile, then yes going underground would offer some protection as you are distancing yourself from the source - the high atmosphere - so attenuating the effects of the EMP.

But in the case of a sudden catastrophic reversal of the Earth's magnetic field (which has never been known to occur throughout geological history), then going underground you would be putting yourself closer to the source - the Earth's core - so the effect of the EMP would be stronger!

In any case, a much easier way of shielding oneself and sensitive electronic equipment/media from an EMP, or any other sources of electromagnetic radiation, is a 'Faraday Cage'.

Regards