The mysterious seismic pulse that repeats every 26 seconds, coming from the Gulf of Guinea

Storm in the Gulf of Bonny / photo Swandau on Wikimedia Commons

Seismic detectors around the world have been capturing a curious and strange phenomenon for decades. Every 26 seconds the earth emits a pulse, a small microseism barely perceptible, that nobody knows why it happens or what causes it. Until recently, no one knew where it came from either.

The first to document the phenomenon was researcher Jack Oliver from the Lamont-Doherty Geological Observatory at Columbia University, New York, who in the early 1960s found that the signal came from somewhere in the South or Equatorial Atlantic and was strongest during the summer months in the Northern Hemisphere.

Two decades later, in 1980, Gary Holcomb from the United States Geological Survey found that the pulse was more intense during seismic storms (longer than normal microseismic activity). But we had to wait until 2005, when Greg Bensen and a team from the University of Colorado managed to triangulate the pulse and locate its origin: the Gulf of Guinea.

And even more until 2011 for Garrett Euler to limit even more the place of origin to an area of the Gulf of Guinea known as Gulf of Bonny or Gulf of Biafra.

Map of the Gulf of Bonny / photo Eric Gaba on Wikimedia Commons

However, what they failed to do was to determine what is causing this earthquake to repeat itself every 26 seconds, constantly. Euler was of the opinion that the cause would be none other than the waves hitting the coast, while a team from the Institute of Geodesy and Geophysics of Wuhan, in China, believes that it is due to some type of submerged volcanic activity. In fact, the Gulf of Bonny is very close to a volcano on the island of São Tomé.

But to this day the mystery remains unsolved. Since the pulse does not cause any discomfort, at least evident, nor is it apparently perceived more than by the advanced technology of modern seismographs, nor does it cause any damage, it is not a priority. There are other, more important things that seismologists focus on in their research.


Sources

Discover Magazine / Jack Oliver, A worldwide storm of microseisms with periods of about 27 seconds. Bulletin of the Seismological Society of America 52 (3): 507–517 / L. Gary Holcomb, Microseisms: a twenty-six-second espectral Line in long-period Earth motion, Bulletin of the Seismological Society of America Vol.70, No.4 pp.1055-1070, August 1980 / N.M.Shapiro, M.H.Ritzwoller, G.D.Bensen, Source location of the 26 sec microseism from cross-correlations of ambient seismic noise, Geogphysical Research Letters, vol.23, L18310, doi:10.1029/2006GL027010, 2006