Seismic Evidence Shows Mars's Valles Marineris Canyon Is Still Tectonically Active
Scientists at Columbia University and Imperial College London have found direct seismic evidence that the largest canyon system in the solar system remains geologically active today. A marsquake detected by NASA's InSight lander originated beneath Valles Marineris and was caused by rocks slipping along a fault deep within the planet's crust, billions of years after the canyon first formed.
The finding challenges the view that the vast Martian canyon system is a dead fossil landscape. It suggests that faults established during the formation and early evolution of Valles Marineris billions of years ago remain weak enough to rupture under stresses acting on Mars today. On Mars, a seismic signal does not necessarily mean a fault has ruptured, because meteoroid impacts, landslides and other processes can also send vibrations through the planet.
The researchers studied a seismic event known as S0976a, recorded by the InSight lander on August 25, 2021. The event was unusual because it came from the opposite side of Mars from the lander and was the only marsquake detected during the mission that could be located in the planet's western hemisphere. Previous work had placed the event near western Valles Marineris, but its cause remained uncertain.
To determine what produced S0976a, the team analyzed how different seismic waves traveled through Mars and arrived at InSight. From the amplitudes and directions of those waves, they reconstructed the motion at the source. The best explanation was a strike-slip marsquake, in which blocks of crust move horizontally past one another along a steep, deeply rooted fault. The rupture occurred roughly 20 to 40 kilometers beneath the surface of western Valles Marineris. The team tested alternative explanations, including meteoroid impacts, landslides and other forms of mass movement, but those models could not reproduce the observed seismic waves. Examination of satellite images of the likely source region taken after the event found no fresh impact crater or large new landslide.
Valles Marineris stretches nearly 3,900 kilometers across Mars, reaches up to 600 kilometers wide and is more than 9 kilometers deep. That makes it nearly nine times longer, more than 20 times wider and about five times deeper than the Grand Canyon at their respective maximum dimensions, the largest canyon system in the solar system. The study was published in Nature Communications.
"Valles Marineris is one of the most spectacular geological structures anywhere in the solar system, but until now we didn't know for certain that its faults are still active," said Jung-Hun Song, lead author of the study from Imperial's Department of Earth Science and Engineering. "What we see is that this is not just a 'dead' fossil landscape, as faults deep beneath the canyon can still slip and generate marsquakes, long after the geological processes that originally formed them have ceased."
Song said the result is compelling because several different types of evidence point in the same direction. "The seismic waves tell us that there was a sideways sliding motion on a fault well below the surface, while the geology seen from orbit shows a region crossed by long-lived fault systems." He added that the study opens up possibilities for discovering ongoing seismic activity on other planetary bodies that might otherwise be considered geologically inactive, a line of inquiry the researchers identify as the next direction for this work.