Being sensitive to low frequencies can be a mixed blessing, so I have a lot of sympathy for those residents of Auckland’s North Shore who have been reporting humming or buzzing sensations in recent times.
Sensitivity to low frequencies isn’t one of those “gifts” that are often relegated to the field of the paranormal, it’s simply one of the many variations that show up in the human population. Just as human eyesight varies from perfect 20/20 vision through to no eyesight at all, the ability to hear and sense movement varies within the population as well.
In the case of hearing, the range of frequencies that we can hear tends to change with age, exposure to loud noise, medical conditions and our physical environment. But, within the population, there are individuals who have extremely sensitive hearing – some have an ability to hear higher frequencies while others are sensitive to frequencies at the lower end of the audible spectrum.
Sensitivity to low frequencies can be a nuisance when local hoons are driving past with their sub-woofers thumping, a heavy freight train crawls past at about 15 km/h, or some loose material is vibrating in the wind. It also mystifies friends who are proud of their home theatre systems that leave me rather tired after watching a movie with the sub-woofer shaking the room for a couple of hours. However, these are usually short duration annoyances that can be minimised or soon pass.
More annoying is the air-conditioning motor with a faulty bearing which causes the concrete floor slab in an office block to tremble with passing low frequency waves. Many people might notice it when their attention is drawn to it, but they are mystified that it can be so annoying to someone sensitive to low frequencies who is standing on the floor slab.
At various times, I have surprised friends by saying “Righto, here we go,” several seconds before they begin feeling an earthquake. On some occasions, this can be due to the fact that I’ve noticed the faster p-wave from an earthquake passing through, but more often its because I’m sensitive to the slower s-wave from a more distant earthquake – the s-wave is often described as “like a diesel locomotive approaching” when people report earthquakes that they have felt.
Being slightly sensitive to lower frequency vibrations does have its advantages when running a site like this one, as I can sometimes notice a weak s-wave from a distant earthquake and investigate further. This was certainly the case late on the evening of May 16th when a magnitude 7.4 quake struck south of Raoul Island. Whilst the quake was felt at many locations in New Zealand, it was only lightly felt as a series of three buzzing waves here on the rock in Tawa. However, it was sufficient to alert me to the quake so that I could pay attention to the crockery and glassware gently rattling in the cupboards – something that wouldn’t have been noticed with the radio playing.
This sensitivity is similar to the motion sensitivity experienced by people known as “poor sailors” who are easily separated from their breakfast by the gentle swaying of a boat. Whilst I am sensitive to low frequencies, I am a relatively “good” sailor, and generally only get queasy when the smell and sound of fellow passengers “hurling” on the Cook Strait run gets too much. Several years ago, I was working on the 20th or 22nd floor of the BNZ tower in central Wellington and found the gentle swaying of the building following large gusts from a northerly gale was a, cough, breeze. However, some other members of the team working on the project found it too much and went home early in the afternoon, while one particularly green specimen refused to return.
But back to low frequency sensitivity. There have been reports in the media in recent days of some people in the Auckland area experiencing a low frequency humming or buzzing. Unfortunately for them, its not just a five minute experience, but an on-going effect that is preventing sleep and, in the words of at least one sufferer, driving them “nuts.” Media commentator Russell Brown has brought together a number of links on the phenomenon in this article on the Public Address website.
Fortunately, some scientists don’t have the blinkers on and are taking an interest in the matter. Brown’s column links to several articles that deal with unusual low frequency phenomena, but not all are relevant to what is being experienced by the Aucklanders who seem to be sensitive to an effect at about 56 Hertz. The article on ocean waves relates to signals less than 1 Hz, and the item about the signals detected before and after the Loma Prieta earthquake that caused damage in San Francisco discusses electromagnetic waves at frequencies below 10 Hz. However, they still make interesting reading.
Interestingly, there doesn’t seem to have been much work done on a possible volcanic cause. It is well-known that magma moving at shallow depths causes volcanic tremor to appear on seismometers and, when activity increases, to be felt by humans and animals. Auckland is built on an active volcanic field, so it isn’t stretching belief that a slight change in the field might cause a very light on-going tremor over a long period of time. This doesn’t imply that an eruption is likely, it’s simply an aspect of volcanic field activity. From memory, volcanic tremor occurs in the low to mid 20 Hz range, so for the 56 Hz effect to be a first harmonic signal the tremor would have to be at 28 Hz which reassuringly doesn’t add much weight to a possible volcanic link.
Geonet operate an extensive network of seismometers to monitor tectonic and volcanic activity near and within New Zealand, and several of the instruments can be viewed in near-real time on the Internet. However, Geonet’s site does not cover the Auckland volcanic field.
The Auckland Regional Council operate the Auckland Volcano-Seismic monitoring Network (AVSN) in conjunction with GNS Science. The data from the network is not published on the Internet in real time, but the ARC’s website features information on the AVSN and lists 15 earthquakes detected by the network since 1995, none of which were volcanic. However, the list is somewhat out of date, and doesn’t record the swarm of events experienced near Waiheke Island last November.
It would be interesting to know if any light tremor has been detected by the AVSN. In the meantime I will be keeping an eye out to see what Dr Moir and his team from Massey University, who were reported to have detected the 56 Hz effect in this NZ Herald article, find from further investigation.