Seismic Reflection Survey of the Kentland Impact Structure

The Kentland Impact Structure is a heavily eroded complex impact crater located in NW Indiana. Despite numerous previous geophysical investigations, the dimensions of the crater have remained unknown. Based on the findings of those studies, it was noted that a disturbed area reached radially outward 6 – 6.5 km from the central peak of the crater, leading to it being documented as a 12.5 – 13 km diameter crater despite lack of further supporting evidence. We conducted a high-resolution active source seismic reflection survey to delineate the crater’s outer faults and boundaries and refine its diameter estimation. Over 300,000 source-receiver arrival times were picked from the dataset, which formed the foundation for constructing a comprehensive tomographic velocity model. This model was used to guide the structural processing of the reflection profile. To aid in the interpretation of the seismic profile, we utilized a reference borehole located near the survey area to identify the local stratigraphy and geologic reflectors. We also digitized Tudor’s (1971) gravity data, which provided valuable support for our tomographic model and processed seismic profile. The seismic profile and tomography revealed a low velocity, ‘seismically transparent’ central zone that matches up with the edge of the moat identified in the digitized gravity data. The reflectors to the right of the central zone remain undisturbed and the gravity data shows no signs of disturbance beyond the rim of the moat. The work carried out provides extensive evidence that the apparent diameter of the crater is ~8.6 km.