STRUCTURE OF CHICXULUB PEAK RING AND SHALLOW CRATER FLOOR FROM NEW SEISMIC DATA

The 2005 seismic survey of the Chicxulub impact crater included a grid of deep reflection profiles collected with a 6 km streamer and a large airgun source, which was also recorded on an array of ocean bottom seismometers (OBS). Refractions collected on the streamer provide detailed velocity information to a depth of about 2 km, by being transformed via the tau-p domain into a well resolved seismic velocity map, which incorporates the Tertiary crater fill and the upper part of the crater itself. Tomographic inversion of the travel-time data from the OBS gives a fully 3D model of seismic velocities to a depth of about 7 km. The velocity information from both techniques may be correlated closely with events seen on the seismic reflection profiles to allow structural and lithological interpretation.

About a kilometre below the crater floor there is an indistinct low frequency reflector which correlates with high seismic velocities and may represent the top of the melt sheet. The event is sub-horizontal and has an uneven surface, and may be identified both inside and outside the peak ring, but not beneath it, where lower velocities persist to depths of several kilometres. The characteristic peak ring is in many places correlated with a reflector dipping beneath its outer edge towards the crater centre, which may represent a plane of reverse movement, possibly bringing the peak ring structure outward over the downthrown terraced blocks beneath.

We present a seismic velocity and reflection interpretation of a grid of profiles around the proposed offshore deep drill-hole through the peak ring, in the context of the deeper 3D velocity structure derived from tomographic inversion.