decouple

To unlink; to take apart or come apart.

radiation decoupled from matter

to decouple a spent rocket stage

To muffle the seismic waves of (a nuclear explosion) by performing it underground.

Smaller explosions and decoupled tests would be permitted. Further, the United States proposed that the three powers should start intensive research on the improvement of methods for detection and identification of underground explosions […]

Decoupled tests would be nuclear explosions set off in massive underground caverns, a site that would greatly reduce the seismic waves caused by the explosion.