Earthquake activity, Tom knew, tends to occur in circular patterns, like bands around the earth—for instance, the circum-Pacific belt, and another belt extending eastward from the Mediterranean through Asia and on into the East Indies. Often these quake lines are visible as breaks or ruptures along the ground surface, called fault traces. No doubt, Tom thought, there were many more uncharted ones.
Could an enemy scientist be making use of these earth faults to produce a man-made quake? Tom mulled over the disturbing idea.
"How would I tackle the job myself, if I had to undertake such a project for national defense?" the young inventor mused. He felt a growing sense of excitement as an idea began to take shape in his mind.
What about an artificial shock wave!
An hour later Bud Barclay walked into the laboratory and found Tom hunched over a jumbled pile of reference books on his workbench.
"What cooks, skipper?" Bud asked.
Tom looked up, his blue eyes blazing. "Bud, I think I may have the answer!"
Tom got up from his stool and paced about the laboratory. "Suppose the Brungarian rebel scientists have invented some sort of shock-wave producer—a device for sending vibrations through the earth's crust or the mantle underneath."
"Okay, suppose they have," Bud replied.
Tom snatched up a piece of chalk and made some quick diagrams on a blackboard. "Just this, pal. Let's say they set up two or three stations around the world for sending out such waves in a definite direction. Wherever the wave crosses an earth fault or another wave—boom! An earthquake!"