Throughout the last 26 seconds for 60 years, seismologists have detected a ubiquitous pulse emanating from the depths of the Earth. The debate about the cause of this mysterious "microseism" has been going on for decades and has produced several convincing hypotheses, but scientists still do not know for sure what is behind the phenomenon.
First observed and recorded by geologist Jack Oliver in the early 1960s and studied in greater detail in the decades that followed, the pulse is known to be stronger during storms. But storms don't go out and rekindle every 26 seconds, nor do volcanoes, whose source has also been proposed.
In 2005, a graduate student named Greg Bensen tracked the origin of the pulsation to a narrower location, a single source in the Gulf of Guinea off the west coast of Africa; six years later, another team refined it even further, locating the origin in an area of the Gulf of Guinea called Bonny Bay.
This team believed that waves crashing on this coast were responsible for the seismic wave. Others, however, were not convinced. Some believed that the Sun itself was the cause. While tectonic activity, earthquakes and volcanoes regularly trigger solid seismic sound, a softer soundscape of seismic static extends almost to infinity.
Mike Ritzwoller, a seismologist at the University of Colorado at Boulder who has been studying the pulse for decades, says that while the pulse is a mystery, seismic activity in general is not.
"Seismic noise exists primarily because of the Sun," whose energy strikes the equator and the poles unevenly, creating wind, storms, ocean currents and waves, all working to move and converge energy on the coastline.
"It's like tapping on your desk. It deforms the area near your joint, but then it's transmitted all over the table," Ritzwoller explains. "So someone sitting on the other side of the table, if they put their hand, or maybe their cheek, on the table, they can feel the vibration. »
With the advent of more advanced tools and technologies, scientists have been able to study the pulse more closely and generally agree that Bonny Bay is the ground zero for everything that happens. Currently, many researchers are beginning to think that the cause could be that this specific location on the edge of the enormous North American continental shelf (well below the ocean floor) is actually the other end of the desk that Ritzwoller uses as a metaphor. In other words, a drum the size of a continent is somehow consolidating its reverberations in one place.
Some researchers still believe that volcanism is the solution and cite as evidence an active volcano on the island of São Tomé in the Bay of Bonny.
Why one of these physical phenomena would produce such a strange clock pulse every 26 seconds remains a mystery.
"We're still waiting for the fundamental explanation of the cause of this phenomenon," Ritzwoller says with a touch of optimism for the next few decades of seismology. "I think the point [of all this] is that there are some very interesting fundamental phenomena on earth that are known to exist there and remain secret. »
Can anyone say more?
First observed and recorded by geologist Jack Oliver in the early 1960s and studied in greater detail in the decades that followed, the pulse is known to be stronger during storms. But storms don't go out and rekindle every 26 seconds, nor do volcanoes, whose source has also been proposed.
In 2005, a graduate student named Greg Bensen tracked the origin of the pulsation to a narrower location, a single source in the Gulf of Guinea off the west coast of Africa; six years later, another team refined it even further, locating the origin in an area of the Gulf of Guinea called Bonny Bay.
This team believed that waves crashing on this coast were responsible for the seismic wave. Others, however, were not convinced. Some believed that the Sun itself was the cause. While tectonic activity, earthquakes and volcanoes regularly trigger solid seismic sound, a softer soundscape of seismic static extends almost to infinity.
Mike Ritzwoller, a seismologist at the University of Colorado at Boulder who has been studying the pulse for decades, says that while the pulse is a mystery, seismic activity in general is not.
"Seismic noise exists primarily because of the Sun," whose energy strikes the equator and the poles unevenly, creating wind, storms, ocean currents and waves, all working to move and converge energy on the coastline.
"It's like tapping on your desk. It deforms the area near your joint, but then it's transmitted all over the table," Ritzwoller explains. "So someone sitting on the other side of the table, if they put their hand, or maybe their cheek, on the table, they can feel the vibration. »
With the advent of more advanced tools and technologies, scientists have been able to study the pulse more closely and generally agree that Bonny Bay is the ground zero for everything that happens. Currently, many researchers are beginning to think that the cause could be that this specific location on the edge of the enormous North American continental shelf (well below the ocean floor) is actually the other end of the desk that Ritzwoller uses as a metaphor. In other words, a drum the size of a continent is somehow consolidating its reverberations in one place.
Some researchers still believe that volcanism is the solution and cite as evidence an active volcano on the island of São Tomé in the Bay of Bonny.
Why one of these physical phenomena would produce such a strange clock pulse every 26 seconds remains a mystery.
"We're still waiting for the fundamental explanation of the cause of this phenomenon," Ritzwoller says with a touch of optimism for the next few decades of seismology. "I think the point [of all this] is that there are some very interesting fundamental phenomena on earth that are known to exist there and remain secret. »
Can anyone say more?