Monitoring Records Sea Floor Spreading Event at Mid-Ocean Ridge for the First Time: Aseismic Fault Slip Found to Be Responsible for Over 95% of Fault Slip and Earthquakes for the Remainder

      As a student and practitioner of geology, I have been instructed about the process of seafloor spreading at the mid-ocean ridges. This is where new oceanic basaltic crust is created from the mantle, from lava flow events under the sea emanating between tectonic plates that are spreading or rifting apart.  When the lava cools, it becomes crust.

     Recently, in the Indian Ocean, a seafloor spreading event was observed directly and monitored in real-time for the first time. The findings were published in Nature. The event began on April 26, 2024, about two months after the monitoring system was deployed. An article about it in Scientific American notes:

“The feat required a small armada of instruments—acoustic transponders, pressure gauges, hydrophones (underwater seismic microphones) and geodetic beacons—deployed across a tectonically active stretch of a mid-ocean ridge.”

“After installing the instruments, the team simply had to wait. But they didn’t have to wait long.”

“Less than two months later a swarm of earthquakes ripped along the ridge. The seafloor dropped about four meters (13 feet), the plates pulled apart by more than one meter (three feet), and up to 160 million cubic meters of lava—the volume of more than 60 Great Pyramids of Giza—erupted onto the seabed. “We were expecting to measure a few centimeters of horizontal displacement and maybe a few centimeters of vertical displacement,” says lead author Jean-Yves Royer of the Laboratory of Planetology and Geodynamics of Nantes in France. In a single event, the ridge accommodated nearly 40 years’ worth of plate motion. It’s an important distinction: though the plates separate at about the speed fingernails grow, that growth isn’t smooth. Instead decades of motion can be released in sudden bursts of earthquakes and volcanic activity.”

     One surprising find from the study was that it was not earthquakes that caused most of the slipping of the faults, but something known as “aseismic slipping,” where the fault slips without measurable earthquaking and likely under the influence of the magma. This would explain why there are not more earthquakes reported at mid-ocean ridges than there should be. The researchers found that in this case, the earthquakes accounted for only 10 to 20 centimeters of that motion (presumably of the 4 meters of motion). That is only 2.5 to 5 percent of the motion.

“That was a surprise,” Royer says.

“It’s not just that there is aseismic slip,” Mark says. “It’s that it happens at the same time as—and probably is causally linked to—the magma.”

 

 

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Scientists get clearest view yet of a spreading seafloor: A rare eruption in the Indian Ocean let researchers capture one of the clearest views yet of a seafloor spreading event. Sam Macdonald. edited by Andrea Thompson. Scientific American. July 8. 2026. Scientists get clearest view yet of a spreading seafloor | Scientific American

Anatomy of a seafloor spreading event captured by in situ seismogeodesy. Jean-Yves Royer, Jean-Arthur Olive, Sara Bazin, Valérie Ballu, Anne Briais, Lise Retailleau, Pierre-Yves Raumer, Edgar Lenhof & OHA-GEODAMS Scientific party. Nature. July 8, 2026. Anatomy of a seafloor spreading event captured by in situ seismogeodesy | Nature