5:15 PM - 7:15 PM
[PPS08-P20] Temperature Dependence of Elastic Wave Velocities of Anorthite and Quartz in Lunar Temperature with Molecular Dynamics Simulation
Keywords:Molecular Dynamics Simulation, Anorthite, Quartz, Seismic Wave Velocity , Lunar Exploration
The lunar highland crust is mainly composed of anorthite , and the evaluation of its elastic properties is essential for lunar exploration. Apollo 17 ambient noise data analysis has revealed that the lunar elastic wave velocity changes negatively correlated with temperature change (Sens-Schonfelder & Larose, 2008), but the cause of this temperature dependence is not fully understood. In this study, to clarify the cause at the mineral scale, we estimate the effect of temperature change on elastic wave velocities by analyzing the temperature dependence of quartz as a comparison to anorthite in a lunar environment using molecular dynamics simulations.
This study used molecular dynamics simulations with GROMACS to calculate the elastic constants of anorthite and quartz over a temperature range of 100 K to 350 K. The simulations applied the ClayFF force field and equilibrated the system under NPT and NVT ensembles. Stress-strain simulations determined the elastic constants, which were used to calculate elastic wave velocities. The results were evaluated as relative velocities with 300 K as the reference and compared with existing experimental data to assess their reliability and accuracy.
The analysis of temperature dependence in P-wave and S-wave velocities for anorthite and quartz revealed a decreasing trend with increasing temperature. In anorthite, the P-wave velocity showed a more significant decrease than the S-wave velocity, suggesting that thermal expansion in the crystal structure influences this trend. In quartz, the P-wave velocity exhibited greater temperature dependence than in anorthite, while the S-wave velocity remained relatively stable. Comparing both minerals, anorthite generally showed lower elastic wave velocities than quartz, likely due to its more deformable structure.
Additionally, the properties of the ClayFF force field led to an overestimation of elastic wave velocities in both minerals. To improve the accuracy, applying a different, more suitable force field should be considered. This study quantitatively evaluated the effect of temperature changes on elastic wave velocity, enabling a better understanding of the lunar subsurface structure while accounting for temperature-dependent velocity variations. These findings also contribute to modeling of elastic velocities associated with water resources on the Moon in the lunar polar regions.
This study used molecular dynamics simulations with GROMACS to calculate the elastic constants of anorthite and quartz over a temperature range of 100 K to 350 K. The simulations applied the ClayFF force field and equilibrated the system under NPT and NVT ensembles. Stress-strain simulations determined the elastic constants, which were used to calculate elastic wave velocities. The results were evaluated as relative velocities with 300 K as the reference and compared with existing experimental data to assess their reliability and accuracy.
The analysis of temperature dependence in P-wave and S-wave velocities for anorthite and quartz revealed a decreasing trend with increasing temperature. In anorthite, the P-wave velocity showed a more significant decrease than the S-wave velocity, suggesting that thermal expansion in the crystal structure influences this trend. In quartz, the P-wave velocity exhibited greater temperature dependence than in anorthite, while the S-wave velocity remained relatively stable. Comparing both minerals, anorthite generally showed lower elastic wave velocities than quartz, likely due to its more deformable structure.
Additionally, the properties of the ClayFF force field led to an overestimation of elastic wave velocities in both minerals. To improve the accuracy, applying a different, more suitable force field should be considered. This study quantitatively evaluated the effect of temperature changes on elastic wave velocity, enabling a better understanding of the lunar subsurface structure while accounting for temperature-dependent velocity variations. These findings also contribute to modeling of elastic velocities associated with water resources on the Moon in the lunar polar regions.