Fig. 4

adapted from the Apollo core samples, and the geometry of the regolith models is introduced in "Method" section. The implanted low-permittivity zone is assumed to be supported by basaltic plates (relative permittivity of 7.5). The thickness of the basaltic plates is assumed to be 0.2 m. The roof shape is adapted from the modeling results shown in Fig. 3f. The heights of the low-permittivity zones vary according to the assumed relative permittivity (i.e., denoted as “per”) among the models, which ranges from 1–3 with an interval of 0.5. The width of the low-permittivity zone is not constrained (e.g., set to 2 m here), but this parameter does not affect our purpose ("Dielectric constant of the low-permittivity zone") section. Multiple-layered structures at a shallower regolith (Fa et al. 2015) are implanted, which have an assumed relative permittivity of 5. The first row shows the 5 model setups from the 1st to the 5th, the second row lists the observed and simulated radargrams, and the third row lists the annotated lower hyperbolic echo pattern (red curves)