School Winner: Why does the Earth hum?

Winning Entry LancasterSchool2C Ankita Hajara with model

On Earth, there is a constant low frequency vibration resounding through the planet. These vibrations are inaudible to most people but a very small percentage of people can hear them. This strange sound is often referred to as ‘The Hum’ and has made the headlines on newspapers in the UK many times. The most famous example in Britain is the Bristol Hum which occurred in the late 1970s. 800 people claimed to have heard the sound and some suffered from nosebleeds and severe headaches as a result. In the 1990s, doctors at Addenbrooke’s Hospital in Cambridge blamed patients being able to hear the hum on tinnitus until someone confirmed that the cause was an external factor. The hum is said to be heard more prominently when indoors and during the night and many people describe the sound as “a diesel car idling in the distance.” The hum has also been felt in many other parts of the world such as in New Zealand, America and Australia.

So, what causes the hum?  Scientists have been speculating the cause of the hum for many years and according to a recent study in Geophysical Research Letters, this micro-seismic activity is mostly due to ocean waves. Previously, it was thought that the vibrations were caused either due to giant ocean waves moving along the sea floor or the interaction between two colliding ocean waves but these theories each only accounted for a few of the many types of vibrations within the hum.

Recently, these two models were combined together and it was found that both these theories put together explained the complete spectrum of vibrations. The colliding waves generated seismic waves with longer wavelengths whereas the giant waves on the ocean floor generated waves with a longer range of frequencies and the hum is mostly a result of these latter types of waves.

Understanding this micro-seismic activity can help scientists chart more detailed maps of the Earth’s interior as well as helping them to be able to predict faraway earthquakes.

Ankita Hajra
Year 12 student
Lancaster Girls’ Grammar School 

I am Ankita and I represent Lancaster Girls’ Grammar School. I have always been very interested in science, especially in the human anatomy and the science behind natural phenomenons so writing an entry for the blog was perfect for me as it allowed me to research some current scientific issues and focus on one in detail. I also have a strong interest in music and play the violin and the piano and enjoy playing these in my spare time.

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