Just a thought about earthquakes.

Say you have a swimming pool. Put a cork in it, floating near the middle.

Now splash the water with your hand. A wave moves out and part of it reaches the cork, and makes it rise a little.

Now splash the water from 2 equidistant points simultaneously. The waves will reach the cork at the same time and move it up even more, or, the same amount with less of a splash made.

From Three or more points, you can initiate waves to coincide at any point depending on the location of the splashes and their timing. The more initiation points, the smaller they can be, and the less noticeable they are.

Waves travel through rock. Want to create an earthquake at a designated target?