Geologic constraints on clandestine nuclear testing in South Asia

Cavity decoupling in salt is the most plausible means by which a nation could conduct clandestine testing of militarily significant nuclear weapons. The conditions under which solution-mined salt can be used for this purpose are quite restrictive. The salt must be thick and reasonably pure. Containment of explosions sets a shallow limit on depth, and cavity stability sets a deep limit. These constraints are met in considerably <1% of the total land area of India and Pakistan. Most of that area is too dry for cavity construction by solution mining; disposal of brine in rivers can be detected easily. Salt domes, the most favorable structures for constructing large cavities, are not present in India and Pakistan. Confidence that they are adhering to the Comprehensive Test Ban Treaty (CTBT) is enhanced by their geological conditions, which are quite favorable to verification, not evasion. Thus, their participation in the CTBT is constrained overwhelmingly by political, not scientific, issues. Confidence in the verification of the CTBT could be enhanced if India and Pakistan permitted stations of the various monitoring technologies that are now widely deployed elsewhere to be operated on their territories.