Casey Braccia

University of Maryland

Experimental Constraints on Physical Properties of Volcanic Rocks with Implications for Lunar Exploration

The lunar subsurface is a primary science target for future missions to the Moon and serves as a potential host location for resources such as water ice, void spaces for astronaut shelter, and important ore bodies for in-situ manufacturing and building materials (Horz, 1985; Coombs and Hawke, 1992; Wendell, 2017). Here we conducted laboratory experiments to investigate how the seismic signature obtained at or near the lunar surface is related to subsurface material properties and structures. A range of analog basaltic samples collected from the San Francisco Volcanic Field (SFVF) in Arizona, Kilbourne Hole (KH) in Southern New Mexico, and Lava Beds National Monument (LBNM) in Northern California are collected and their geophysical properties are measured. The relationships between the seismic wave velocity and porosity of basaltic rocks from different locales are obtained and the measured velocities are compared to local seismic surveys of the sample locale.

Using laboratory techniques, the SFVF basalts P-wave and S-wave velocities range from ~5 km/s to ~6 km/s +/- 0.1 km/s and ~2.1 km/s to ~3 km/s +/- 0.1 km/s, respectively. For the KH basalts P-wave and S-wave velocities range from ~3.5 km/s to ~4.4 km/s +/- 0.1 km/s and ~1.8 km/s to ~2.3 km/s +/- 0.1 km/s, respectively. For LBNM basalts P-wave and S-wave velocities range from ~3.1 km/s to ~6 km/s +/- 0.1 km/s and ~1.2 km/s to ~2.4 km/s +/- 0.1 km/s, respectively. A relationship between the porosity and velocity of basalts from these three locations was determined. Using the field seismic data for each study site and the relationship derived from the laboratory seismic data and porosity, the amount of possible large-scale fracturing is derived. Based on these experimental measurements, we estimate the large-scale fractures and voids are ~85 vol% at the SFVF, ~40 vol% at the KH, and ~40 vol% at the LBNM. These results provide quantitative constraints for subsurface exploration in future lunar surface missions.