Lunar near‐surface shear wave velocities at the Apollo Landing Sites as inferred from spectral amplitude ratios

Abstract

We reexamined the horizontal‐to‐vertical amplitude ratios of the long‐period seismograms to determine the shear wave velocity distributions at the Apollo 12, 14, 15, and 16 lunar landing sites. Average spectral ratios, computed from a number of impact signals, were compared with spectral ratios calculated for the fundamental mode Rayleigh waves in media consisting of homogeneous, isotropic, horizontal layers. The shear velocities of the best fitting models at the different sites resemble each other and differ from the average for all sites by not more than 20% except for the bottom layer at station 14. The shear velocities increase from 40 m/s at the surface to about 400 m/s at depths between 95 and 160 m at the various sites. Within this depth range the velocity‐depth functions are well represented by two piecewise linear segments, although the presence of first‐order discontinuities cannot be ruled out.

Mesoscopics of ultrasound and seismic waves: application to passive imaging

“…Cooper et al [141], using travel time inversion of refracted P -waves, found that the compresionnal wave velocity beneath the Apollo 17 site was around 100 m/s from 0 to 4 m depth and then 327 m/s from 4 to 32 m depth. Our shear wave profile thus complements and is consistent with previous observations [141,145]. Thus, by comparing these profiles, we can conclude that the v P /v S ratio of the Lunar regolith is ∼2.…”

Exogenic Dynamics, Cratering, and Surface Ages

“…Reevaluation of published lunar geophysical data (Horvath et al, 1980;Toksoz et al, 1972) by Lognonne et al (2003) shows longitudinal seismic velocity as low as $1 km s À1 above $1 km depth below the lunar surface and an increase of 3-4 km s À1 to a depth of $5 km, which is in agreement with and constrains the validity of a porous scaling law for lunar impacts applied for a 1 km thick upper layer (Ivanov, 2006). Present results from the GRAIL mission suggest significant density variations for the …”

Lunar noise correlation, imaging and monitoring

“…Our shear wave profile thus complements their P-wave profile, giving the v P /v S ratio of the lunar regolith at this site of ~2. The present result is also consistent with the S-wave velocity profiles derived from the H/V spectral amplitude ratios at other Apollo sites (Horvath et al, 1980), where they generally increase from 40 m/s at the surface to about 400 m/s at depths between 95 m and 160 m. …”