Those big nukes we and the Soviets tested back in the day were very large and heavy, and impractical for use as strategic weapons. The largest warheads ever deployed on an ICBM by any nation were the US 9 Mt W53, mounted atop the Titan II ICBM, and the Soviet 20 Mt Mod-1 warhead, mounted atop the Soviet SS-18 ICBM. All the Mod-1s were decommissioned by 1984, and all the Titan IIs were decommissioned by 1988.
Current strategic nuclear arsenals contain warheads with yields in the sub-megaton range, and rely on multiple, smaller warheads and enhanced accuracy to destroy targets.
Because nuclear war with Russia (or any other nation) is very unlikely, our primary concern is with terrorist nukes, which would be crude and have relatively low yields, probably in the 5-10 kt range at best. While this would be enough to destroy the core of a major city, people living even 5 miles away would survive the blast relatively unscathed. Of course, there would still be the potential for massive fires and societal disruption that could affect those near the city, but outside the damage area.
Bottom line is, if you live 20 or more miles outside a major city that gets hit by a terrorist nuke, you’d probably not know that a nuke went off in the city until you heard it on the news.
TD, thanks for the info. Good stuff.
Depending on the size of the nuke the terrorists were able to obtain, of course. If they got a hold of a Hiroshima-sized fission bomb (around 15 KT) you'd be safe at 20 miles, but I suspect you'd see a flash of light and hear a helluva noise. But most likely they'd only be able to get something in the 1 - 3 KT range. ....or less.
YouTube has film of the 50+ MT Tsar Bomb detonation, not surprisingly.