The Earth appears to have a mysterious pulse that repeats itself every 26 seconds. The phenomenon has been known for decades, but even the most advanced instruments have not been able to completely unravel the origin of this signal.
Like the rhythmic beating of a heart or the regular ticking of a clock, the earth’s crust produces a slight seismic noise every 26 seconds. These “beat” tiny earthquakes, known as microseisms, are imperceptible to humans, but are easily recorded by the highly sensitive instruments used by seismologists, writes BBC Science Focus.
Although scientists discovered this rhythmic pulse several decades ago, even today there is no consensus on its cause.
Microseisms are, in fact, quite a frequent phenomenon. They are constantly generated by natural events, from ocean waves hitting shores to the synchronized movements of excited spectators in stadiums. These phenomena create a kind of “background noise” seismic. However, this microseism is unusual because of its constant and perfectly rhythmic character.
Geologist Jack Oliver, who was working at Columbia University in the early 1960s, is credited as the researcher who identified this “global microseismic”. He then concluded that the source of the pulse was somewhere in the southern Atlantic Ocean.
More than half a century later, using much more powerful tools, researchers have been able to determine much more precisely where the signal is coming from. They discovered that the pulse originates in an area in the Gulf of Guinea off the west coast of Africa known as the Bight of Bonny.
There are two hypotheses
Currently, researchers consider two main explanations: ocean waves or volcanic activity.
According to the first theory, the strong and fast waves reflecting off the coast of Africa would concentrate in a certain area of the ocean, near the island of Bioko. When these waves hit the edge of the continental shelf, their energy could very easily deform the earth’s crust, thus generating a regular pulse of seismic waves.
An important argument in favor of this hypothesis is that the intensity of the 26-second pulse appears to be directly related to the strength of storms in the South Atlantic Ocean. The stronger the storms, the more energetic the waves hitting the seabed in shallow areas, and the more intense the generated seismic waves.
But there is another hypothesis. Researchers in China claim that a volcano on the island of São Tomé could be responsible for this phenomenon. It wouldn’t be the first time a volcano is associated with microseismic activity.
For example, Mount Aso, a volcano in Japan, produces seismic vibrations that are believed to be generated by the movement of gases and magma underground. Later, scientists identified a second source of regular microseisms in the same region, which provides an additional argument for the volcanic explanation. This second pulse has a slightly different frequency and occurs every 28 seconds.
The signal appears to originate near the Pico Cão Grande volcanic formation located on the island of São Tomé in the Gulf of Guinea. This finding suggests that the 28-second pulse may have a volcanic origin, and the researchers speculate that the 26-second pulse may also come from another yet-to-be-identified volcano.
Despite these promising clues, scientists have not yet been able to determine with certainty what causes it “heartbeat” seismic of the Earth.
Although the regularity of this pulse continues to arouse the interest of researchers, the phenomenon does not appear to represent a danger. For this reason, its study has so far not been a major priority for seismologists, the publication also notes.
