3D geometry of the Lonar impact crater, India, imaged from cultural seismic noise

Abstract

The Lonar impact crater in the Deccan Volcanic Province of India is an excellent analogue for impact-induced structures on the Moon and other terrestrial planets. We present a detailed architecture of the crater using a high-resolution 3-D seismic velocity image to a depth of 1.5 km through the inversion of ambient noise data recorded over 20 broadband seismographs operating around the crater. The ambient noise waveform is dominated by cultural noise in the 1-10 Hz band. The shear wave velocity (Vs) model is created from Rayleigh wave group velocity data with a horizontal resolution of 0.5-1 km in the period range of 0.1-1.2 s. A key feature of the model is a velocity reduction of 10-15 % below the crater compared to outside the ejecta zone. The low-velocity zone below the crater is nearly circular and extends to a depth of ~500 m. This estimated crater’s depth is consistent with global depth-diameter scaling relations for simple craters. The basement, with a Vs of more than 2.5 km/s, lies beneath the Deccan basalt, which has a Vs of ~2.4 km/s. These results are consistent with laboratory-measured data from the Lonar crater and borehole data in the western Deccan trap. This study opens a new window for exploring impact craters and sub-basalt structures using high-frequency ambient noise tomography.

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

“…The depth of the original crater floor of Lonar is a debatable issue. Various researchers suggested it to be 509 m (Pilkington & Grieve, 1992), 500–600 m (Rajasekhar & Mishra, 2005), >600 m (Sivaram et al., 2018), and 500 m (V. Kumar & Rai, 2023). Our seismic image places the original crater floor at a depth of 400 m (Figure 8), similar to the borehole information at Lonar crater (Chandran et al., 2021; Fredriksson et al., 1973).…”

“…An in‐depth analysis of the 3D sub‐surface V S image of Lonar crater would reveal the nature of the sub‐surface beneath the impact crater, particularly, the heterogeneity of target rocks beneath the impact craters, crater‐fill deposits, impact damage zones, mineralized zones, hydrothermal alteration zones, groundwater aquifers and rock materials of astrobiological significance. These details of the crater are poorly known, despite the previous studies (e.g., V. Kumar & Rai, 2023; P. S. Kumar et al., 2014; Sivaram et al., 2018).…”

“…Considering these aspects, Lonar crater provides important insights into impact cratering processes in basaltic targets on Mars, where fluvial activities greatly shape the impact craters and geochemically alter the basaltic target rocks (e.g., P. S. Kumar et al., 2014). Although several studies offered important insights into the geological setting of Lonar crater (e.g., Fredriksson et al., 1973; Fudali et al., 1980; P. S. Kumar, 2005; P. S. Kumar et al., 2014; Maloof et al., 2010), geophysical studies of this crater are limited (e.g., V. Kumar & Rai, 2023; Rajasekhar & Mishra, 2005; Sivaram et al., 2018). The nature of the sub‐surface in and around Lonar crater is still poorly known.…”

“…(2018) provided the V S model for Lonar crater up to a depth of 750 m using the joint modeling of the H/V Spectral Ratio (HVSR) and Rayleigh wave dispersion from the ambient noise cross‐correlation. They estimated the true crater depth to be ∼600 m. A recent study by V. Kumar and Rai (2023) carried out an ANT study of Lonar crater, using a limited data set, and provided the seismic images below Lonar crater. Neither of these studies reported the details of the impact damage beneath the crater and impact trajectory for the impact event.…”