Sharp-edged phenomena require high-frequency waves far above human hearing

Evidence

The edges of the energy pattern are particularly dense with dots. These are the so-called caustics, where the energy is highest and which just might explain the sharp clean edges found in the sod divots and cookies. Such a well-defined accumulation of compression wave energy requires high frequencies, and no doubt a very shallow source so that the easily attenuated high frequencies survive to the surface. According to f λ = c, a 5 cm wavelength at c = 6000 m/s corresponds to a frequency of 120,000 Hz—well above human hearing. Of course, lower frequencies would be present too; they could not carve such a well-defined structure, but would make the event quite audible. — Eric J. Heller, Why You Hear What You Hear- An…, 713

Categorization

• DEFINE: Defines caustics as regions of concentrated wave energy that explain sharp physical edge effects.
• CANDY: The fact that a 5 cm wavelength in rock equals 120,000 Hz—far above hearing—is a light, sharable tidbit.