A New Lunar Crustal Thickness Model Constrained by Converted Seismic Waves Detected Beneath the Apollo Seismic Network
Résumé
Analysis of conversions between compressional and shear waves is a workhorse method for constraining crustal and lithospheric structure on Earth; yet, such converted waves have not been unequivocally identified in seismic data from the largest events on the Moon, due to the highly scattered waveforms of shallow seismic events. We reanalyze the polarization attributes of waveforms recorded by the Apollo seismic network to identify signals with rectilinear particle motion below 1 Hz, arising from conversions across the crust-mantle boundary. Delay times of these converted waves are inverted to estimate crustal thickness and wavespeeds beneath the seismometers. Combined with gravimetric modeling, these new crustal thickness tie-points yield an updated lunar crustal model with an average thickness of 29-47 km. Unlike previous models, ours include explicit uncertainty estimates, offering critical context for future lunar missions, geophysical studies, and predicting 15-36 km crust at Schrödinger and 29-52 km at Artemis III sites.
Plain Language Summary The Moon's crust holds key information about its formation, evolution, and surface processes. Using seismic data from the Apollo missions, we identified moonquake seismic signals arising from the boundary between the Moon's crust and mantle, allowing us to obtain new estimates of crustal thickness beneath the Apollo landing sites. These signals had previously been difficult to detect due to extensive scattering caused by the highly fractured and heterogeneous lunar crust. By integrating our seismic estimates with gravity and topography data, we developed an updated global map of the Moon's crustal thickness, revealing an average thickness of 29-47 km and providing uncertainty quantification not available in previous models. Our results provide vital insights into the Moon's interior structure and offer valuable guidance for future lunar exploration and sustainable human activities on the Moon.
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