Undersea City — Frederik Pohl; Jack Williamson

It was the most dreaded of all undersea phenomena. If strong enough, it would set up chain-reaction pressures that could shatter any dome and cost inestimable lives. But the Krakatoan Dome has been specifically designed to cope with the tremors of its seaquake-prone area. The trouble was, all of a sudden, there were more quakes than any of the experts had counted on... quakes that no one could possibly have forecast because they hadn't come from natural causes.

The Sub-Sea Academy had assigned Cadet Jim Eden to the Krakatoan Dome to find out what was going on, and for very special reasons. First, he was more at home in the underwater world than most anyone else. But, even more important, they sent Jim because his uncle was suspected of being the heinous saboteur!