The study titled “Tectonics and Seismicity of the Lunar South Polar Region” by Watters et al. (2024) provides important insights into the tectonic activity and seismic hazards in the lunar south polar region, with important implications for future lunar missions, including NASA’s Artemis program.
The lunar south polar region has garnered significant attention in recent years due to its potential for future human exploration and the presence of water ice in permanently shadowed craters. This comprehensive study examines the tectonic features, seismic activity, and slope stability in this area, with particular focus on the proposed Artemis landing sites.
Tectonic Features in the South Polar Region
The study reveals that the lunar south pole is not immune to the global compressional stresses affecting the Moon. These stresses result in contractional deformation, primarily expressed as lobate thrust fault scarps. Using high-resolution imagery from the Lunar Reconnaissance Orbiter Camera (LROC), researchers have identified 15 lobate scarps within 150 km of the south pole.
Key features include:
The Wiechert cluster: A group of at least five individual fault scarps located at approximately 86.7°S, 146.7°E, with a maximum relief of about 10 meters.
The Ibn Bajja cluster: Three individual fault scarps at roughly 86.6°S, 185.3°E, with a maximum relief of about 20 meters.
The de Gerlache scarps: Located within 60 km of the south pole, with the largest scarp being approximately 4 km long and having a relief of 60-80 meters.
Seismic Activity and Potential Hazards
The study suggests that some of these fault scarps may still be active, potentially generating moonquakes. Of particular interest is the correlation between the de Gerlache scarp and a significant shallow moonquake (SMQ) recorded by the Apollo Passive Seismic Experiment in 1973, known as the N9 event.
Key points on seismicity include:
Magnitude: The N9 event had an estimated body wave magnitude (M_b) of 5-5.6, making it one of the largest moonquakes recorded.
Modeling: Simulations suggest that a slip event on the de Gerlache fault could generate a moonquake with a moment magnitude (M_w) of approximately 5.3.
Ground shaking: Such an event could produce strong to moderate ground shaking within a 40 km radius and moderate to light shaking beyond 50 km.
Slope Stability and Landslide Risk
The study assessed the potential for seismically induced landslides in the south polar region using an infinite-slope stability model. This analysis identified areas most susceptible to regolith landslides during seismic events.
Key findings on slope stability:
Shackleton crater: Large portions of the interior walls of Shackleton crater are predicted to be unstable and susceptible to landslides.
Critical ground acceleration: The acceleration needed to trigger a 1-meter thick landslide on slopes greater than 30° is relatively low, about 2.3% of lunar gravity.
Water ice influence: The presence of water ice in the regolith could significantly increase cohesion, potentially stabilizing steep slopes against shallow landslides.
Implications for Artemis Landing Sites
The study’s findings have important implications for the proposed Artemis III landing sites:
Seismic hazards: The potential for strong seismic events should be considered when planning and locating permanent outposts.
Landing site risks: Seismic hazards may affect the proposed Artemis III landing sites, particularly the de Gerlache Rim and Nobile Rim 1 regions.
Regolith stability: Even light seismic shaking could trigger regolith landslides, especially in areas with low regolith cohesion.
Summary
This comprehensive study of the tectonics and seismicity of the lunar south polar region provides valuable insights into the potential hazards facing future lunar missions, including the Artemis program. By identifying active fault scarps, modeling potential moonquakes, and assessing slope stability, the research contributes important information for the planning and execution of safe and successful lunar exploration endeavors.
As humanity prepares to return to the Moon through the Artemis program, understanding and mitigating these seismic risks will be essential for establishing a sustainable presence on our celestial neighbor.
