Numerical Simulation of Lunar Seismic Wave Propagation: Investigation of Subsurface Scattering Properties Near Apollo 12 Landing Site

One of the most critical issues associated with the analysis of lunar seismic data is the intense scattering, which prevents precise seismic phase identifications, thereby resulting in poor constraints on the internal structure of the Moon. Although some studies estimated subsurface scattering properties from analyses of the Apollo seismic data, the properties have large uncertainties and are still open issues to be resolved to improve the inner structure model of the Moon. While the previous studies tried to constrain the scattering features within the lunar crust mainly from data analysis, this study estimated them from a numerical approach. We constrained the scattering properties near Apollo 12 landing site by conducting seismic wave propagation simulations under various parameter settings and comparing the synthetics with the data. As a result, we succeeded in reproducing seismic signals excited by the Apollo artificial impacts. This led to a constraint on the scattering properties, such as typical scale and thickness of heterogeneity, around the Apollo 12 landing site. The derived structure suggests that the intense scattering structure exists down to 20 km at the northern portion of the region of the Apollo 12 landing site, and to 10 km at the southern region from the landing site. In addition, our model requires a smaller P- and S-wave velocity ratio (1.2-1.4) compared with those conventionally considered (>1.73). This implies a dry and porous environment consistent with laboratory measurements of terrestrial samples and reasonable with the generalized lunar environment.

Automated summary

The study estimated scattering properties in the lunar crust through numerical simulations near the Apollo 12 landing site, successfully reproducing seismic signals excited by artificial impacts. It revealed the intense scattering structure extending down to 20 km in the northern region and to 10 km in the southern region from the landing site, requiring a smaller P- and S-wave velocity ratio compared to conventional values.