Mechanics of Second Order Faults and Tension Gashes

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Research Article| November 01, 1969 Mechanics of Second Order Faults and Tension Gashes E. Z LAJTAI E. Z LAJTAI Department of Geology, The University of New Brunswick, Fredericton, New Brunswick, Canada Search for other works by this author on: GSW Google Scholar GSA Bulletin (1969) 80 (11): 2253–2272. https://doi.org/10.1130/0016-7606(1969)80[2253:MOSOFA]2.0.CO;2 Article history received: 14 Aug 1968 rev-recd: 07 May 1969 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation E. Z LAJTAI; Mechanics of Second Order Faults and Tension Gashes. GSA Bulletin 1969;; 80 (11): 2253–2272. doi: https://doi.org/10.1130/0016-7606(1969)80[2253:MOSOFA]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The origin of en echelon second order shear fractures and tension gashes associated with first order, or primary, faults is examined analytically and experimentally. It is postulated that en echelon second order structures form under the influence of a stress mechanism similar to the one occurring in the direct shear test. The direct shear or modified direct shear state of stress could develop at certain points along a forming primary fault as a result of a local reduction in the normal stress acting on planes perpendicular to the displacement direction. It is argued that in most en echelon arrays the orientation of the individual fractures reflects the existence of a local state of stress, and cannot directly be correlated with the regional (primary) stress field. The zone in which they occur, however, may represent planes of high effective shear stress within the regional framework.The direct shear model (full relief of transverse normal stress) offers a stress mechanism which can explain the origin of not only en echelon tension gashes but also second order faults. For a given set of strength parameters, the type of en echelon fractures that will develop depends on the normal stress acting in the primary fault plane. In general, tension fractures form at low normal stress, shear fractures at intermediate values of normal stress, and at high normal stress a crush or shear zone is produced. If the state of stress is one of modified direct shear (only partial relief of transverse normal stress), the development of second order faults is favored. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.