TRANSVERSE WAVE INTERFERENCE
On this slide we show the orthodox representation of EM wave interference.
The chart is stylized since we assume two single-frequency EM waves which intersect and interfere in the indicated region.
In the interference zone, in-phase wave amplitudes add (constructive interference) while out-of-phase wave amplitudes subtract (destructive interference). In our stylized mode, we show the zero-summed locations as lines.
Conventionally, these interfering waves are considered to be transverse waves in vacuum.
The point is, in this scheme we think of "putting in the waves of finite amplitude, and creating the zero-amplitude regions by destructive interference." We create additional waves of increased-amplitude regions by constructive interference.
Note that this view is only half correct. It addresses the electromagnetics, but not the gravitational aspects. Actually the regions of destructive EM interference are regions of constructive G-interference, and the regions of constructive EM interference are regions of destructive G-interference.