HR: 16:00h
AN: T14A-01 INVITED    [Abstracts]
TI: The Geology of Impact Fragmentation and Crater Controlled Fracture Networks
AU: * Asphaug, E
EM: asphaug@pmc.ucsc.edu
AB: Overall, the study of planetary impact crater physics has made significant advances in the past two decades, thanks to modeling and observation. However, our understanding of the fragmentation network beyond a crater wall remains poorly understood. At the fundamental level, we do not yet understand where the transition takes place, and over what scale, between the so-called "strength regime" (where strength and other rheological properties dominate) and the "gravity regime" of impact crater scaling. The issue is muddled by the fact that numerical shock-hydrodynamical models (hydrocodes) have difficulty accurately evolving a stress tensor in a solid undergoing shock and hydrodynamic motion. Furthermore, the evolution of the stress tensor during the production of gravity-scaled craters is a subject of much debate, for if strength were truly negligible, there would be no final craters. Further still, and of subject here, only a few published efforts have made inroads into the topic of what damage occurs beyond the crater walls in a planetary impact. The latter subject is one of some importance, for it is speculated that large, deep-seated craters on Mars may dominate the subsequent regional hydrologic evolution. If so, then the same may be true, to a more limited extent given its other activity, of Earth's lithosphere. Radial fissures in crater systems, resulting primarily from hoop stresses and listric faults towards the crater interior, may set the stage for post-impact volatile evolution. On Europa, there is evidence that small secondary impact craters create fracture networks in an ice lithosphere a few km thick, and that these fractures accommodate the far-field stresses of impact rebound by connecting into long faults. One Enceladus, Dione, Ganymede and other icy bodies, the effect of impact cratering beyond the rim is observed in fault patterns. Here I present evidence for crater controlled fracture networks in planetary lithospheres, and provide an fundamental overview of what is known about the process of impact fragmentation, at geologic scales, in both high and low strain rate regimes, including the transition from spall spatial scales and high strain rates, to large spatial scales and low strain rates. The principal challenges of implementing realistic fracture models in numerical hydrocodes will be addressed.
DE: 5104 Fracture and flow
DE: 5420 Impact phenomena, cratering (6022, 8136)
DE: 8136 Impact phenomena (5420, 6022)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting