Mars's Valles Marineris, the largest known canyon in the solar system, still has active faults beneath it, according to a reanalysis of a powerful 2021 marsquake, Live Science reported. On Aug. 25, 2021, NASA's InSight lander, which touched down in 2018, detected a quake designated S0976a. It reached magnitude 4.2, at the time the strongest marsquake InSight or any other Mars lander had recorded. A magnitude-4.7 event in May 2022 later took that top spot; S0976a remains second. Unlike most marsquakes, which have been minor tremors from meteorite impacts near the lander, this one was a deep rumble from the opposite side of the planet, in the western half of Valles Marineris. In a study published Oct. 15 in Nature Communications, researchers reanalyzed the seismic waves and concluded that the quake came from a fault running below the canyon, most likely because of tectonic movement in that hidden crack.
"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," first author Jung-Hun Song, of Imperial College London, said in a statement. "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." The canyon is a set of interconnected gullies stretching up to 2,500 miles (4,000 kilometers), roughly 10 times longer than the Grand Canyon, and up to 20 times wider and five times deeper. It was named after the Mariner 9 spacecraft, which helped discover it in 1971, and sits near the Tharsis volcanic region, home to Olympus Mons.
Scientists have long thought Mars's surface has remained relatively unchanged for nearly 3 billion years, Live Science noted, citing the European Space Agency. The planet is smaller than Earth, so its interior has cooled faster, and it has no tectonic plates; its outer layer acts more like a lid over a cooling interior. It still has fault lines, but they are giant cracks in the crust rather than plate boundaries. The new study found what the team called a "slip-strike" marsquake, in which "blocks of crust move horizontally past one another along a steep, deeply rooted fault," somewhere between 12 and 25 miles (20 to 40 kilometers) below Valles Marineris. The researchers also simulated other possible causes, including a major asteroid strike or a landslide in the canyon, and said nothing else could explain the patterns. "What makes the result compelling is that several completely different types of evidence point in the same direction," Song said.
"S0976a has turned out to be an extraordinary event," co-author Doyeon Kim, head of Imperial College London's Terrestrial and Planetary Seismology Lab, said in a statement. "Its waves traveled through the core and helped us investigate the deepest part of Mars, and now they are telling us what happened at the source itself." InSight's mission ended in December 2022, after dust covered its solar panels, so there is currently no way to detect new marsquakes. The study shows that the lander's archived data can still yield discoveries. The verified claim is that one well-studied quake is best explained by a still-slipping fault under the solar system's largest canyon, not that Mars has Earth-like plate tectonics.