The impulse appears every 26 seconds, is imperceptible to humans, but is so strong that it is recorded with sensitive seismological devices around the entire globe. This natural phenomenon has puzzled researchers around the world for almost 60 years.
The seismological phenomenon was examined for the first time on a larger scale at the beginning of the 1960s. The American geologist John Ertle “Jack” Oliver published the article in 1962 in the seismological journal Bulletin of the Seismological Society of America (BSSA)A Worldwide Storm of Microseims With Periods Of About 27 Seconds“by presenting the results of his research on microquakes.
Microquakes every 26 seconds
The quakes appeared in an interval between 26 and 27 seconds and Oliver located this epicenter in the Gulf of Guinea. On June 6, 1961, the earthquakes were investigated for eight hours and measured in 16 of 18 research stations across the globe. He compared the strongest rash with an explosion of around 600 tons of TNT. The strength fluctuates over time; Oliver found that the winter months of the southern hemisphere had the greatest momentum.
At first, microquakes are nothing special. The earth is shaking in Germany like this almost every daywithout anyone outside of seismological research being aware of it. The corona crisis even improves research, as the Exit restrictions reduce the sources of everyday interferencethat otherwise easily overlay these quakes.
Quake as a monitor of the soil conditions
The findings from this are helpful for research – liquids and gases can be responsible for the stress conditions in wet rock. Therefore, more information about the nature of the rock can be gained from the measured microquakes.
The difference is the periodicity. And that makes it so difficult for researchers to locate the source of this phenomenon. And Jack Oliver was limited by the technical possibilities of his time; so he could only speculate.
Hypotheses between wave impact and magnetic activity
The main hypothesis was that the microquakes were caused by waves hitting the coast in the Gulf of Guinea. A second hypothesis was that magnetic activity under the South Atlantic was causing the quakes.
In August 2006 it was published in the journal Geophysical Research Letters published an article, in which the researchers narrow down the place of origin for the pulse (0.038 Hz) more precisely. The microquakes were detected in the Bay of Bonny, in the Gulf of Guinea as well as in the Antipodean Pacific region east of Papaua New Guinea.
New findings from the Chinese research team
A Chinese research team published in 2013 in the Geophysical Journal International another specialist article to the phenomenon. They discovered a second periodic pulse (0.036 Hz). While they assume the Sao Tome volcano as the source as the origin for the known impulse due to the local proximity, the possible cause of the newly discovered source remains in the dark. The researchers suspect volcanic activity there too.