Here are some starter materials. A lot of the public information (that a non-Q cleared physicist could calculated from) comes from a single paper written in the early 60s.
It is difficult finding baseline information for this investigation. Here's a first cut at some good sources. Dates very widely over last 20 years.
NMD good info 2001 http:// web.ihep.su/library/pubs/tconf01/ps/c4-3.pdf (NMD in 2001)
NK new ICBM https:// www.csis.org/analysis/north-korea%E2%80%99s-new-icbm
Missile Defense 2020 https:// missilethreat.csis.org/missile-defense-2020/ (17 years later)
UN overiew (no technical info, 1991) https:// unoda-web.s3-accelerate.amazonaws.com/wp-content/uploads/assets/HomePage/ODAPublications/DisarmamentStudySeries/PDF/SS-21.pdf - contains table of strategic weapons at end of cold war.
Very useful on physics, if old: http:// ece-research.unm.edu/summa/notes/TheoreticalPDFs/TN368.pdf
http:// www.dtic.mil/dtic/tr/fulltext/u2/a477653.pdf (MHD-EMP (1992) - 38 MB PDF!)
http:// www.futurescience.com/emp/ferc_Meta-R-321.pdf (E3 pulse from high altitude burst - effect on power grid - 2010)
E1 component is classic EMP (prompt gamma) - arrives in under 1 microsec
E2 is similar in timing/spectrum to EM radiation produced by lightening. 1 microsec - 1 second
E3 is 10s to 100s second, very low frequency, and similar to geomagnetic disruptions due to solar flares or CME events.
The E3 component ('MHD EMP') is much less intense in its electric field, but can cause grid collapse esp since protection equipment may have been badly damaged by E1. It has two peaks – at 10 sec the 'blast wave' and at 100-300 sec the 'heave', a long slow surge, like a geomagnetic storm, and likely with similar consequences.
The E3 component is a plasma wave, and is shielded if the burst is able to create an 'X Ray ionised' patch in the sky. It has to travel first as an Alven wave horizontally to the edge of this patch. before it can continue to the ground. The direct signal diffuses through the ionised patch, if there is one, in about 10 seconds, due to the 'skin effect'. The 'heave' signal is caused by upward expansion of the heated air. The Heave falls off as 1/r^3 (similar to a magnetic dipole).
A deliberate EMP effect would need a weapon specifically designed not to create the 'X Ray ionised' patch.