If you live near Cartago and you think you are seeing ghosts, the apparition may not be Aunt Millie.
That also is true out on the Pacific earthquake belt.
Scientists generally discount the supernatural that cannot be demonstrated by evidence. So it is only natural that there are studies linking low-frequency sound emitted by volcanos or earthquakes with feelings of dread or even ghosts.
Researchers call 18.98 Hz the ghost frequency because of the effect it has on humans. One researcher even says that this frequency can cause tricks with the eyes.
New Zealand paranormal investigators reported an increase in ghost sighting after a major earthquake there one year. Of course, the ghost hunters attributed this increase in the collapse of houses and the jostling that disturbed the spooks. But one also could argue that aftershocks were producing low-frequency sounds that are not audible to human ears.
Ham radio operators know that there is a range of low-frequency sounds emitted by the earth itself. This may be one reason why dogs and horses can sense earthquakes before humans. Not all are in the ghost frequency range.
There have been experiments in England that have shown that these frequencies can affect humans. There even is a book, “Ghosts in the Machine,” that discusses the creation of low frequencies by fans and other devices in daily use.
With the Turrialba volcano continuing to act up, there is a good chance that low-frequency sounds are being created.
When gas and magma move up the vents, pressure is exerted on the interior volcano walls creating sounds that scientists can capture on sensitive instruments. The sounds usually are 20 Hz and lower.
These low-frequency sound waves also can travel much further than audible sounds, hence the possibility of Aunt Millie.