The largest earthquake ever detected on Mars has revealed layers in its crust that may indicate past collisions with massive objects such as meteoroids. Previous data have suggested that oversized effects have occurred in the past, and the findings provide evidence that may support this hypothesis.
The research, led by UCLA planetary scientists, is published in two papers Geophysical Research Lettersmay also indicate alternating layers of volcanic and sedimentary rocks beneath the surface.
The magnitude 4.7 quake, or Marsquake, occurred in May 2022, lasted for more than four hours, and released five times the energy of any quake ever recorded. While modest by Earth standards, the quake was powerful enough to send seismic surface waves completely around Earth’s circumference, a phenomenon that has been observed for the first time on Mars.
Readings taken from InSight, which landed on Mars in 2018. InSight is the first outer-space seismometer to delve into the “inner space” of Mars: its crust, mantle and core.
“The seismometers on the InSight lander recorded thousands of Martian quakes, but none of this magnitude had ever occurred, and it took more than three years to record them after touchdown,” said corresponding author, professor of Earth, planetary and space sciences Caroline Beghein said. “This earthquake produced different kinds of waves, including two types of waves that were trapped near the surface. Only one of these two types of waves has been observed on Mars, and after the two impact events, it has never been observed in a Martian earthquake Pass.”
Mapping seismicity, location and frequency of impacts on Mars, and interior structure will be important for future missions to the Red Planet as it will inform scientists and engineers where and how to build structures to keep future human explorers safe.
As on Earth, studying how seismic waves travel through rocks can give scientists clues about the temperature and composition of Earth’s subsurface, which can help inform the search for groundwater or magma. It also helps scientists understand the forces that shaped Earth in the past.
Beghein’s group combined measurements of two types of surface waves, called Love and Rayleigh waves, to infer the speed of subsurface shear waves, which travel horizontally and move rock perpendicular to the direction of wave travel. This is the first time Love waves and Rayleigh waves have been observed simultaneously on Mars.
Measurements show that when rocks between 10 and 25 kilometers underground vibrate in a direction nearly parallel to the planet’s surface, shear waves move faster in the crust than when the rocks vibrate perpendicularly.
“This wave velocity information is associated with deformations in the interior of the crust,” Began said. “Alternating volcanic rocks and sedimentary layers deposited long ago, or very large impacts, such as meteoroids, are likely responsible for the seismic wave measurements we observe.”
The data also allowed Jiaqi Li, a UCLA postdoctoral researcher in Beghein’s group, to understand that shear waves move faster in the southern highland regions of Mars than in the northern lowland regions. The northern hemisphere of Mars has a lower altitude and more craters than the southern hemisphere. The prevailing theory to explain the origin of this difference has had a huge impact on the lowlands.
New data suggest thick sedimentary rock accumulations and relatively high porosity in the lowlands. Large amounts of gas, such as air in sedimentary rocks, slow the waves down.
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