A new approach for gravity modeling of complex impact structures on earth based on their strain distribution

Abstract The processes of crater formation relevant to impact‐induced fracturing of the target are illustrated and linked with the variation of bulk strain with depth, as extracted from numerical modeling. To this, the concept of remaining impact induced porosity was studied based on measured formation porosity data from deep drilling in two complex impact structures, Puchezh‐Katunki and Ries, resulting in a common porosity depth relation. The analysis of the strain distribution revealed a pattern of systematic strain regimes associated with complex impact structures. The bulk strain distribution calculated across the whole width of the model crater allows data from the ring basin of the Ries structure to be combined with the central uplift data of the Puchezh‐Katunki structure. The measured formation porosity includes the effects of lithostatic pressure and hydrothermal overprint and represents the porosity remaining after impact. The common porosity‐depth relation is then correlated with the bulk strain distribution derived by the numerical modeling for a complex impact crater. The bulk strain distribution combined with the empiric porosity relation results indirectly in the density structure of complex impact craters. The obtained density distribution differs considerably from conventional thinking as it was found that an upper common density region is characteristic for the whole upper part of the collapsed crater interior, including both the mega breccia ring basin and the central uplift. Our approach provides an additional constraint improving the accuracy in gravity modeling of complex impact structures. The derived relation between bulk strain and porosity was applied to calculate the gravity effect of the model crater and compare it with the measured gravity anomaly of a similar sized impact structure.