Unveiling the Moon's Hidden Secrets: A New Global Map Reveals Recent Tectonic Activity
The Moon's Surface is More Dynamic Than We Thought
Imagine a vast, dark landscape, pockmarked with ancient craters and smooth, flat plains. Now, picture low, winding ridges crisscrossing these plains, like faint seams in cooled wax. These features, known as Small Margin Ridges (SMRs), have long been overlooked, but a new study has brought them into sharp focus, revealing a hidden world of recent tectonic activity on the Moon.
A Shrinking Moon's Fingerprint
The Moon and Earth both flex and crack, but they do it in different ways. Earth's surface is broken into plates that grind, collide, and spread apart. The Moon's crust, however, is not divided into plates, yet it still carries internal stresses that shape the landscape. One of the most common tectonic landforms on the Moon is the lobate scarp, a ridge created when the crust compresses and one block of material pushes up and over another along a fault. These scarps are mainly found in the lunar highlands, and earlier work found they formed within the last billion years.
In 2010, Tom Watters, a senior scientist emeritus at the Center for Earth and Planetary Studies, reported evidence that the Moon is slowly shrinking. This global contraction helped explain the lobate scarps in the highlands. But not all young compression features fit neatly into that picture. SMRs are part of what was missing.
A Catalog That Suddenly Got Much Bigger
The team built what it calls the first exhaustive catalog of SMRs. In the nearside maria alone, they identified 1,114 new SMR segments, raising the known total of SMR segments across the Moon's maria to 2,634. These features form from the same kind of compressional forces as lobate scarps, but they appear only in the maria. This difference matters because the maria cover large portions of the nearside and some patches of the farside. If young faults also thread through these plains, the Moon's most familiar 'landing' terrain may be more tectonically active than many people assume.
How Young is 'Young' on the Moon?
The authors argue that SMRs belong among the youngest tectonic features on the Moon. They estimate surface 'seismic resetting' ages for five nearside SMR clusters that range from about 50 million to 310 million years. The idea behind seismic resetting is that fault slip and moonquakes can erase small impact craters near a fault. The team assumed SMR-related quakes could wipe out craters smaller than 100 meters in nearby areas, which would alter the crater size-frequency distribution used for dating. Even with that caveat, the ages cluster in a striking range, with an average SMR seismic resetting age of 124 million years.
Peeking Under the Ridge, Then Counting the Strain
To connect these ridges to specific fault geometries, the team modeled a subset of SMRs using elastic dislocation modeling with USGS Coulomb 3.4 software. The sample is limited: 13 SMR segments across seven clusters, chosen largely because terrain model coverage was available. For those modeled faults, the dip angle ranged from 30° to 45°, with an average of 38°. Estimated slip ranged from 15 to 110 meters, averaging 44.7 meters. Fault depths ranged from 30 to 200 meters, averaging 101.2 meters. The team also estimated how much the maria have strained due to this late-stage contraction, finding an areal contractional strain of 3.41 × 10⁻⁵ to 3.95 × 10⁻⁵, or 0.0034% to 0.0040%, across the maria.
The Moonquake Question Gets Wider
Watters' earlier work linked lobate scarp activity to shallow moonquakes. If SMRs form from the same global stress fields and similar thrust-fault mechanics, then the maria may host their own widespread set of quake sources. The study points to Apollo-era seismic observations for context, noting that shallow moonquakes in the magnitude range of 1.6 to 4.2 were detected by the Apollo Lunar Seismic Experiment, and suggests quakes in that range could contribute to crater erasure near active faults. The authors argue that young tectonics and related seismicity are not confined to highlands terrain, and they list future mission concepts that could benefit from the new map, including the Lunar Geophysical Network, the Lunar Environment Monitoring Station, and the Farside Seismic Suite.
But Here's Where It Gets Controversial...
The study's findings raise questions about the Moon's tectonic activity and the potential for future moonquakes. While the authors argue that SMRs are among the youngest tectonic features on the Moon, the exact ages and their implications for the Moon's seismic history remain uncertain. The team's modeling of SMRs and their connection to fault geometries is a step forward, but more research is needed to fully understand the Moon's dynamic landscape and the hazards it may pose for future missions.
