What is the primary frequency range and dominant propagation effect for surface waves?

The primary frequency range for surface waves is from 30 kHz to 300 kHz. This range is significant because surface waves, which typically follow the contour of the Earth, can effectively propagate along the ground and can diffract around obstacles. The dominant propagation effect for these waves is diffraction, which allows them to bend and continue to follow the terrain even with various obstacles in the way.

Understanding the mechanism of diffraction is crucial as it enables communication and signal transmission over extended distances by allowing the waves to spread out and navigate various barriers, thus sustaining the signal even in less-than-ideal conditions. This characteristic is vital in applications such as maritime communication and certain types of military operations where range and terrain variability are factors to consider.

In contrast, the other frequency ranges provided do not effectively correlate with surface wave propagation and the mentioned propagation effects, leading to their exclusion as the correct choice.