UNDERSTANDING THE RIES CRATER SUBSURFACE FROM HIGH-RESOLUTION SEISMIC DATA

The 15 Ma, 26 km wide Ries Crater in southern Germany is a well preserved mid-sized impact crater. Although well studied, existing questions about Ries include determining the subsurface crater morphology and emplacement mechanisms of the crater suevite (a polymict, impact melt bearing breccia). The diameter of Ries is near the 25-30 km threshold to form a peak ring however current interpretations identify a crystalline ring formed by an inward collapsed and upturned crater rim in contrast to a true peak ring formed by material outwardly collapsing from a central uplift. Proposed suevite deposition processes at Ries include fallback from an impact plume, melt flows, impactoclastic density currents, and melt-water (sometimes called molten fuel-coolant) interactions.

In August 2017, we collected 4 seismic profiles in the Ries Crater, Germany, imaging one half of the crater profile from outside the southern crater rim to the crater center. We present 2 seismic profiles of the inner crater which display the subsurface structure of Ries. These high-resolution data image post impact lacustrine sediments, suevite, and crystalline basement showing the subsurface morphology. We use the Nördlingen 1973 core descriptions and sonic log as well as the low-resolution 1968 seismic data aid our interpretation of the subsurface. Deep hummocky reflectors in the central basin are interpreted as remnants of a collapsed central uplift. This morphology places Ries Crater near the upper limit of a central peak crater where dynamic collapse occurred but was limited in duration and extent. Within the central crater, we image a high amplitude layered unit wherein the geometry of the reflectors is suggestive of deposition as lateral flows. Based on core-log-seismic integration, this unit is either crater suevite deposited as impactoclastic flows or a post-impact deposition of reworked suevite. Either result has implications for the timing and geometry of impact and post-impact processes at Ries.