The noise cross‐correlation approach for Apollo 17 LSPE data: Diurnal change in seismic parameters in shallow lunar crust

Abstract

[1] By applying the noise cross-correlation technique to Apollo 17 Lunar Seismic Profiling Experiment (LSPE) data, we discovered temporal changes in Rayleigh-wave group velocity within a diurnal cycle (29.53 d). Assuming that this phenomenon is caused by density and seismic parameter changes due to temperature, we formulated an inverse problem. Thermal diffusivity 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 (k % 10 À6 m 2 /s) is too large to fit the data. Our preferred value is about k % 10 À7 (m 2 /s), although the inversion alone cannot discriminate among the values below this number. Differences between this estimate and a lower estimate (k % 10 À8 m 2 /s) by Langseth et al. 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. 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., M. Eitzel, and T. Yano (2008), The noise cross-correlation approach for Apollo 17 LSPE data: Diurnal change in seismic parameters in shallow lunar crust,

Planetary Seismology

“…Observed amplitudes on Earth below an angular order of 20 are 0.2 ngals. the investigation of the near-subsurface (Larose et al, 2005;Sens-Schö nfelder and Larose, 2010;Tanimoto et al, 2008). Such a technique was also applied in California on short period (6-20 s) surface waves (Shapiro and Campillo, 2004;Shapiro et al, 2005), and the technique can be applied to shorter-wavelength surface waves as well, as it is sensitive to the uppermost kilometers of the crust.…”

Moon meteoritic seismic hum: Steady state prediction

“…Such detection will also allow a better assessment of more ambitious goals in lunar seismology, such as the recently proposed detection of strange quark matter impacts [ Banerdt et al , 2006]. Finally, future recording of lunar seismic noise may allow new types of investigations of lunar interior structure, such as recent tomographic studies performed on the Earth using the continuous microseismic noise [ Shapiro and Campillo , 2004; Shapiro et al , 2005], and inversions for very shallow regolith structure on the Moon using high‐frequency thermally induced noise [ Larose et al , 2005; Tanimoto et al , 2008].…”

Lunar noise correlation, imaging and monitoring

“…Also the sensitivity of G 1 to this signal appears to be significantly smaller than that of G 2 -G 4 . Tanimoto et al (2008) tried to explain the zero correlation time peak as an electromagnetic phenomenon that occurs when the Moon resides in the plasma of the Earth's magnetotail but concluded that the occurrence of the signal only in the lunar morning contradicts this hypothesis. Instead they noted that coincident signals for instrument operation may be responsible.…”

“…The phase shift compared to the surface temperature curve excludes the possibility that the RDT variations are caused by technical effects due to heating of the instruments. It also means that it is inappropriate to assume that the variation of subsurface velocity is in phase with surface temperature as done by Tanimoto et al (2008) who compared the velocities during noon and early night. Another observation that supports a relation between the RDT variations and heating by the Sun concerns the amplitudes of the peaks of the RDT.…”

“…Larose et al (2005) first obtained Rayleigh wave Green's functions from this dataset. Later on an attempt to identify seismic velocity changes with Rayleigh waves obtained at different phases of a lunation was made by Tanimoto et al (2008). A continuous measurement of seismic velocity variations was obtained by Sens-Schönfelder and Larose (2008) using coda waves from the noise correlations.…”