Statistics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p51b0484t&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P51B-0484
Statistics
5430 Interiors (8147), 6250 Moon (1221), 6297 Instruments And Techniques
Scientific paper
Analysis of Apollo 17 data (continuous data from 1976 to 1977) by the cross-correlation approach for seismic noise led us to two new discoveries, one related to the source of noise and the other on the periodic changes in seismic parameters due to extreme temperature changes near the surface. It has been shown previously by Larose et al. (2005) that Green's functions, dominated by Rayleigh waves, can be retrieved from cross-correlation of seismic noise in Apollo 17 data. We first confirmed their correlation results and further analyzed the details in GreenA?"qfs functions. The first discovery is that the sources of noise that lead to construction of Green's functions are (most likely) thermal moonquakes. This is suggested in the Rayleigh-wave observations that show diurnal variation (29.5 days) in amplitudes, but one can directly confirm a correlation between the statistics of thermal moonquakes and Rayleigh wave amplitudes. This is in contrast to the terrestrial case where ocean-generated seismic noise plays a critical role in the cross-correlation approach. This has implications for future planetary seismology as many planets lack oceans but may have thermal quakes caused by drastic temperature changes near the surface. Second, diurnal temporal variations in group velocity are detected, showing a strong correlation with the temporal variation of lunar surface temperature. This can be explained by the Sun's thermal effects which cause changes in density and seismic velocities near the surface. These effects are measurable on the moon since surface temperature changes as much as 270 K within the diurnal period. Depending on the thermal diffusivity of the medium, the depth extent of this thermal effect varies considerably. Inversion for thermal diffusivity using the changes in group velocity dispersion resulted in an estimate 10**(-7) (m**2/s) for the upper few meters.
Eitzel Melissa
Tanimoto Toshiro
Yano Tadashi
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