Impact craters are observed on the surfaces of all rocky planets and satellites in our Solar System(1); some impacts on Earth, such as the Cretaceous/Tertiary one that formed the Chicxulub impact crater(2,3), have been implicated in mass extinctions(4-12). The direction and angle of the impact - or its trajectory - is an important determinant of the severity of the consequent environmental damage, both in the downrange direction ( direction bolide travels) and in the amount of material that enters the plume of material vaporized on impact(2,13-15). The trajectory of the Chicxulub impact has previously been inferred largely from asymmetries in the gravity anomalies over the crater(2,3). Here, we use seismic data to image the Chicxulub crater in three dimensions and demonstrate that the strong asymmetry of its subsurface correlates with significant pre-existing undulations on the end-Cretaceous continental shelf that was the site of this impact. These results suggest that for rocky planets, geological and geomorphological heterogeneities at the target site may play an important role in determining impact crater structure, in addition to impact trajectories. In those cases where heterogeneous targets are inferred, deciphering impact trajectories from final crater geometries alone may be difficult and require further data such as the distribution of ejecta
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