Lunar landforms indicate geologically recent seismic activity on the moon

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These lunar lobate scarps are the focus of new research, published in Earth and Planetary Science Letters, that use craters in the surrounding highland landscape as indicators of scarp movement and therefore are ideal candidates for estimating ages.

Explaining the significance of their research, Dr. Jaclyn Clark, of the University of Maryland, said, “Unlike Earth, the moon has no plate tectonics leading many scientists to explore what drives tectonism on the moon and other rocky bodies in our solar system.

“The existence of these small lobate thrust faults suggests that the lunar surface is contracting due to long-term interior cooling of the moon (cooling at a much faster rate than Earth).

“A better understanding of when tectonic activity has occurred and how the seismic energy attenuates through the regolith (unconsolidated rock and dust on top of bedrock) away from the fault by exploring the crater population could help plan safer missions to the moon.”

Using crater size-frequency distribution measurements, Dr. Clark and colleagues determined the ages of 34 lobate scarps on the moon’s surface. They further combined this with previous research to generate a dataset of 60 lobate scarps on both the near side and far side of the moon. Additionally, this data provided information on the magnitude of seismic activity associated with scarp movement and the likelihood of fault reactivation.

To do so, the scientists input high-resolution satellite images taken by the Lunar Reconnaissance Orbiter Camera into geological mapping software ArcGIS to measure the size and frequency of craters within a particular area, permitting calculation of cumulative crater density and an age model.

The research team observed a pattern in age distribution between footwalls (unit of rocks on the underside of a fault) and hanging walls (the unit above the fault thrust upwards) across craters, proximal and distal to the scarp. Proximally, ~38% of footwalls were younger than adjacent hanging walls, 47% the opposite and 15% approximately the same age. For distal scarps, 33% had hanging wall ages over twice that of proximal hanging walls, while distal footwalls were not often considerably older than their proximal counterparts.

Dr. Clark explains, “When we first started doing crater size-frequency distribution measurements at the proximal locations of the hanging wall and footwall, we initially saw that the hanging wall area produced a younger age than the footwall, leading us to think that there may be more seismic shaking in the hanging wall.

“After expanding this method to 34 scarps, we find that this is not the case for all of them. Many scarps have similar ages (i.e., ages that overlap within error) for the hanging walls and footwalls. Most differences in ages are between the proximal and distal locations, which is most likely due to the attenuation of seismic energy away from the fault.”

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