Propagation velocity of joints: A debate over stable vs. unstable growth of cracks in the earth

Terry Engelder

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1 Scopus citations

Abstract

One of the hotly debated questions in the geoscience literature as of 2006 concerns the velocity of joint (i.e., a mesoscopic crack in rock) propagation in the crust of the Earth. Earthquake rupture loads rocks at stress rates of many MPa/sec, whereas plate tectonic deformation yields long-term loading rates as much as ten orders magnitude slower. This large range in loading rates leaves open the possibility of joint propagation in rocks anywhere from subcritical (i.e., stable growth) to critical and post-critical (i.e., unstable growth). Several facts are relevant during adjudication of the propagation-velocity debate: 1.) joints are inherently planar but may propagate as gradually curving single surfaces on scales > 10 m, 2.) hackle fringes are relatively rare, and thus, the exception to the planar surface (i.e., ≪1% of all joint surface area in the crust of the earth consists of hackle fringe), 3.) fixed-grips loading is the normal configuration for propagation of joints in the brittle crust of the Earth if there is a fatigue limit, 4.) plume morphology on planar surfaces of joints is consistent with a velocity = f(K1) relationship, 5.) fracture under fixed-grips loading is inherently stable for several reasons, mainly, 5A.) developing elastic properties of a bulk rock with fractures favors stable propagation, 5B.) fluid-drive mechanisms in the earth favor stable propagation. The fractography of rock can demonstrate facts 1, 2, and 4 directly, and facts 3, 5A, and 5B indirectly. In summary, these facts point to a large role for subcritical propagation (i.e., stable growth) in the crust of the Earth whereas critical and post-critical propagation (i.e., unstable growth) in natural rock is exceptionally rare.

Original languageEnglish (US)
Title of host publicationFractography of Glasses and Ceramics V - Proceedings of the 5th Conference on the Fractography of Glasses and Ceramics
Pages457-482
Number of pages26
Volume199
StatePublished - 2007
Event5th Conference on the Fractography of Glasses and Ceramics - Rochester, NY, United States
Duration: Jul 9 2006Jul 13 2006

Publication series

NameCeramic Transactions
Volume199
ISSN (Print)10421122

Other

Other5th Conference on the Fractography of Glasses and Ceramics
CountryUnited States
CityRochester, NY
Period7/9/067/13/06

All Science Journal Classification (ASJC) codes

  • Ceramics and Composites
  • Materials Chemistry

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