Differences in Scattering Properties of the Shallow Crusts of Earth, Mars, and the Moon Revealed by P-Wave Receiver Functions

摘要

The scattering properties of terrestrial planetary bodies can provide valuable insights into their shallow seismic structure, meteoritic impact history, and geological activity. Scattering properties of the shallow crusts of Earth, Mars, and the Moon are investigated by constructing P-wave receiver functions (PRFs) from teleseismic waveforms with high signal-to-noise ratios. The authors' analysis reveals that strong coda waves lead to significant variations in the PRF waveforms calculated using different time windows, and the stability of the PRF is primarily influenced by the fractional velocity fluctuation. Synthetic PRFs for various scattering media confirm these observations. Comparing the observed and synthetic PRFs, it is found that the fractional velocity fluctuation in the shallow crust is greater than similar to 0.2 for the Moon but less than similar to 0.2 for Earth and Mars. The authors further discuss possible mechanisms that could have affected the fractional velocity fluctuation and suggest that the distinct fractional velocity fluctuation between the Moon and Earth/Mars is mainly due to differences in the water content of the crustal rocks of the three planetary bodies. Plain Language Summary Coda waves follow direct P or S waves and comprise scattered waves generated when seismic waves travel through a heterogeneous medium. These incoherent coda waves may interfere with seismic waves from coherent structures and complicate the interpretation of seismic structures. The authors compute P-wave receiver functions (PRFs) of Earth, Mars, and the Moon using teleseismic waveforms with high signal-to-noise ratios. It is found that the PRFs of Earth and Mars are reliable and that the crustal converted waves can be effectively recovered. However, the PRF of the Moon calculated using different time windows is unstable even for direct P waves. The authors demonstrate that the stability of the PRF can be used to characterize the strength of the seismic scattering. Increased scattering by the medium leads to the degradation of the PRF stability. The PRF stability is mainly affected by the fractional velocity fluctuation of the shallow crust, which is larger on the Moon than on Earth and Mars. The fractional velocity fluctuation of the shallow crust is smaller on Earth and Mars because their shallow crusts are hydrous, whereas the shallow crust of the Moon is anhydrous.