What do the seismographs at NOAA show? An explosion of that supposed magnitude should show up as at least a blip on most seismographs.
NOAA doesn’t operate seismographs; the USGS does, linked into a wide variety of international networks (EMSC, IRIS, and the special nuclear explosion monitoring network, the IDC in Vienna.)
There was no seismically-recorded explosion from any network, located remotely near Fordow, at any time remotely near the time when the explosion was claimed to happen.
http://earthquake-report.com/2012/01/19/iran-real-time-earthquakes-list/
Nothing happened at that time on the 21st, in that area of Iran.