Deciphering shallow mantle stratification through information dimension

Applying the concept of cluster entropy, we demonstrate that the primary P-to-s (Ps) conversions originating from the well-recognized seismological boundaries (Moho, 410 km, and 660 km depth interfaces) in Earth's interior and multiple reflections (reverberations) between the surface and the Moho—the prominent crust-mantle boundary of Earth—can be unambiguously identified. Their attendant information dimension can act as a discriminant. Documentation of shallow mantle stratification at depths ∼150–300 km (L/X layers) using Ps signals is scarce and is sometimes attributed to their weak registration in the seismograms together with interference by reverberations from shallow structure. The slopes of best fits to mean cluster information dimension (as function of epicentral distance) of Ps signals from target boundaries such as the Moho, 410 km, and L/X discontinuities are consistently gentle with a slight negative character. In contrast, those related to multiples show a steep positive behavior. This opposite nature can potentially discriminate between reverberations and direct converted waves, even when they tend to arrive in overlapping time windows. Our approach thus enables unequivocal identification of shallow mantle layering from Ps data recorded at diverse tectonic provenances of wide antiquity.