A underground testing can easily be picked up, there is no point of arguing on this anymore.
You can't cover up the nuke blast otherwise pakistani would have tested their tactical nukes.
found it go through this
https://www.nap.edu/read/12849/chapter/5
Too big a document to read:biggrin2:
Still seismograph can only detect earthquake not exactly the clause.
Thermal sensors can only confirm there was a blast not exactly what kind of.
The only sure way is to find ionizing radiation above the blast site. Satellites can analyse to some extent but to confirm one need a sniffing plane just above the blast site to check air samples.
US did this in North Korean case. They wouldn't dare fly a plane over Indian desert.
Without that happening it's all just guessing game. No concrete proof.
Pakistani nukes are already under us scrutiny so is all their possible test sides.
US regularly voids paki airspace so Pakistani can't test tactical nukes.
Even in case of North Korea US first denied any nuke blast and only later accepted certain evidences.
Beside a blast can be contained not completely but most of the radiation can be contained leaving weaker radiation signals.