## The Noise Cross-Correlation Approach for Apollo 17 LSPE Data: Diurnal Change in Seismic Parameters in Shallow Lunar Crust

Toshiro Tanimoto, Melissa Eitzel, & Tomoko E. Yano

Published 2008, SCEC Contribution #1165

By applying the noise cross-correlation technique to Apollo 17 Lunar Seismic Profiling Experiment (LSPE) data, we discovered temporal changes in <br/>Rayleigh-wave group velocity within a diurnal cycle (29.53 days). Assuming that this phenomenon is caused by density and seismic parameter changes <br/>due to temperature, we formulated an inverse problem. Thermal diffusivity <br/>serves as the key parameter for this problem because it controls the depth penetration of temperature change. The results of inversion indicate that a typical number for the thermal diffusivity of terrestrial rocks ($\kappa \approx 10^{-6}$ $m^2/s$) is too large to fit the data. Our preferred value is <br/>about $\kappa \approx 10^{-7}$ ($m^2/s$), although the inversion alone cannot discriminate among the values below this number. Differences between this estimate and a lower estimate ($\kappa \approx 10^{-8}$ $m^2/s$) by Langseth et al. [1973] may indicate the significance of radiation for thermal transfer in the upper-most lunar crust. We also find a direct correlation between the Rayleigh-wave amplitudes and the statistics of thermal moonquakes, both of which change with the diurnal periodicity and peak at sunset. This implies that thermal moonquakes are the source of valuable seismic noise, lending strong support to an idea proposed by Larose et al. [2005]. This is in contrast to the terrestrial situation where the ocean-generated noise plays a critical role in the cross-correlation approach. The noise correlation approach is potentially useful for many planets which undergo wide swings in surface temperature and thus potentially have thermal quakes.

Citation
Tanimoto, T., Eitzel, M., & Yano, T. E. (2008). The Noise Cross-Correlation Approach for Apollo 17 LSPE Data: Diurnal Change in Seismic Parameters in Shallow Lunar Crust. Journal of Geophysical Research: Planets, 113(E08011). doi: 10.1029/2007JE003016.