HR: 09:00h
AN: U21E-05    [Abstracts]
TI: Investigating of the effects of target heterogeneities on terrestrial crater formation.
AU: * Barnouin-Jha, O S
EM: olivier.barnouin-jha@jhuapl.edu
AF: JHUAPL, Johns Hopkins Road, Laurel, MD 20723-6099, United States
AU: Crawford, D A
EM: dacrawf@sandia.gov
AF: Sandia National Laboratory, P.O. Box 5800, Albuquerque, NM 87123, United States
AU: Cintala, M J
EM: mark.j.cintala@nasa.gov
AF: NASA Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, United States
AU: Wada, K
EM: wada@neko.lotem.hokudai.ac.jp
AF: Institute of Low Temperature Science, Hokkaido University, Sapporo, 060-0819, Japan
AB: The shape of terrestrial impact structures such as the Chesapeake or Ries crater indicate how important pre- existing target heterogeneities are even for fairly large impact structures. Both these craters possess an inverted sombrero structure as a result of a weaker sedimentary surface layer overlying a stronger crystalline basement. But beyond such horizontal layering, closer analyzes of the subsurface geology present in these and other terrestrial craters indicate that vertical heterogeneities in the strength and geochemistry of a target are also often present. These may influence the formation and subsequent modification of terrestrial craters. In deed, evidence indicates that at Meteor crater, for example, pre-existing vertical jointing of the target gives this crater its square appearance either by confining and re-directing the shock and subsequent rarefaction waves, or by allowing preferential weathering along zones of weakness at the joints. In this study, we present a series of 2 and 3 dimensional numerical investigations of crater formation in a conceptually simple but physical complex targets: a box of randomly distributed quartz spheres of identical size. These investigation should provide some constraints on how all types of target heterogeneities influence the cratering process at broad terrestrial scales. In this particular study, we analyze the formation of craters using a range of impact velocities, projectile sizes and strength of target components. We also consider a case where we immerse the spheres in a basaltic matrix. Our approach is to use the CTH code, that solves the equations of motion, while conserving mass, energy and momentum using a second order multi-material Eulerian methodology. The adaptive mesh refinement, a fairly new capability of CTH, is paramount to these studies, and allows investigating the effects of fine-scale target heterogeneity on the cratering process, through the use of a simple microscopic models with complex, but resolvable heterogeneous geometries, rather than a complex macroscopic model. Thus, the behavior of the impact shock traversing individual spheres in the target can be modeled, although slip between sphere is difficult for individual spheres separated by void; instead the material of each sphere merge and flow together. These calculations are not intended to exactly reproduce any given observations, but rather provide insights into what factors influence observed trends in shock propagation and excavation. Initial coupling between the projectile, initial distribution of the materials in the target and the presence of the matrix all influence the shape of resulting transient crater cavities. It is the subsequent collapse and modification of such transient craters that produce the structures seen on Earth.
DE: 5420 Impact phenomena, cratering (6022, 8136)
DE: 6022 Impact phenomena (5420, 8136)
DE: 8136 Impact phenomena (5420, 6022)
SC: Union [U]
MN: 2007 Fall Meeting