Letters to Nature

Nature 418, 310-313 (18 July 2002) | doi:10.1038/nature00903; Received 5 February 2002; Accepted 10 June 2002

Dynamic fracture by large extraterrestrial impacts as the origin of shatter cones

Amir Sagy1, Ze'ev Reches1 & Jay Fineberg2

  1. Institute of Earth Sciences, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel
  2. The Racah Institute of Physics, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel

Correspondence to: Jay Fineberg2 Correspondence and requests for materials should be addressed to J.F. (e-mail: Email: jay@vms.huji.ac.il).

A large impact by a comet or meteorite releases an enormous amount of energy, which evaporates, melts and fractures the surrounding rocks1, 2, 3, 4. Distinctive features of such impacts are 'shatter cones', deformed rocks characterized by hierarchical striated features5, 6. Although such features have been used for decades as unequivocal fingerprints of large-body impacts, the process by which shatter cones form has remained enigmatic. Here we show that the distinctive shatter-cone striations naturally result from nonlinear waves (front waves) that propagate along a fracture front7, 8, 9, 10. This explains the observed systematic increase of striation angles with the distance from the impact. Shatter-cone networks, typically spanning many scales, can be understood as hierarchical bifurcations of the fracture front, which is generated by the immense energy flux carried by the initial, impact-generated, shock waves. Our quantitative predictions based on this theory are supported by field measurements at the Kentland and Vredefort impact sites. These measurements indicate that shatter cones near to the impact site were formed by fractures propagating at nearly the Rayleigh wave speed of the host rocks, whereas the furthest shatter cones observed (about 40 km from the impact site) were formed by fronts moving more slowly. These results provide insight into impact dynamics as well as dissipative mechanisms in solids subjected to sudden, extremely intense fluxes of energy.