Ambient Noise Tomography Reveals Asymmetric Impact Damage Zone Beneath Lonar Crater, India: Implications for Oblique Impact Cratering in Heterogeneous Basalt, With Planetary Applications

Abstract

Meteoroid impacts produce different types of fractures and damage zones beneath impact craters. The 3D geometry of these features reflects the trajectory and energetics of an impact event. In this study, we mapped the impact damage zone beneath the 1.88-km-diameter Lonar crater, emplaced in Deccan basalts, using Ambient Noise Tomography (ANT). A network of 23 broadband seismic stations in and around the crater yielded a 1.2 km deep 3D shear wave velocity (V_S) image covering ∼7 km by ∼5 km area. It revealed ∼500–900-m-thick heterogeneous target basalt flows, underlain by an undulating Archean granite-gneiss basement. A substantial reduction in V_S is observed beneath the crater. The original crater floor was found at a depth of 400 m below the crater rim, which is filled by impact breccia and lake sediments. Beneath the original floor, we found an oval-shaped, asymmetric 200-m-thick lensoidal low-velocity layer with a tongue-like feature beneath the southwestern ejecta blanket. The damage zone is inferred to have formed as a result of oblique impact, in which the projectile arrived from northeast to southwest direction. The V_S reduction in the low-velocity layer was used to calculate the amount of impact damage in it. The oblique impact produced a more elevated southwestern crater rim. Impact-related near-surface fracture zones up to a radial distance of >1 km beneath the ejecta blanket were also found. We suggest that impact damage beneath impact craters on Earth and other planetary bodies may be imaged using ANT.