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Hybrid fracture and the transition from extension fracture to shear fracture


Fracture is a fundamental mechanism of material failure. Two basic types of brittle fractures are commonly observed in rock deformation experiments—extension (opening mode) fractures and shear fractures1,2. For nearly half a century it has been hypothesized that extension and shear fractures represent end-members of a continuous spectrum of brittle fracture types3,4,5,6. However, observations of transitional fractures that display both opening and shear modes (hybrids) in naturally deformed rock have often remained ambiguous, and a clear demonstration of hybrid fracture formation has not been provided by experiments4. Here we present the results of triaxial extension experiments on Carrara marble that show a continuous transition from extension fracture to shear fracture with an increase in compressive stress. Hybrid fractures form under mixed tensile and compressive stress states at acute angles to the maximum principal compressive stress. Fracture angles are greater than those observed for extension fractures and less than those observed for shear fractures. Fracture surfaces also display a progressive change from an extension to shear fracture morphology.

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  1. 1

    Jaeger, J. C. & Cook, N. G. W. Fundamentals of Rock Mechanics (Chapman and Hall, London, 1979)

  2. 2

    Paterson, M. S. Experimental Rock Deformation—The Brittle Field (Springer, Berlin, 1978)

  3. 3

    Hancock, P. L. in Geology in the Real World—the Kingsley Dunham Volume (eds Nichol, I. & Nesbitt, R. W.) 155–164 (Institution of Mining and Metallurgy, London, 1986)

  4. 4

    Engelder, T. Transitional-tensile fracture propagation: a status report. J. Struct. Geol. 21, 1049–1055 (1999)

  5. 5

    Muehlberger, W. R. Conjugate joint sets of small dihedral angle. J. Geol. 69, 211–219 (1961)

  6. 6

    Sibson, R. H. Brittle-failure controls on maximum sustainable overpressure in different tectonic regimes. Am. Assoc. Petrol. Geol. Bull. 87, 901–908 (2003)

  7. 7

    Griggs, D. T. & Handin, J. W. Observations on fracture and a hypothesis of earthquakes. Geol. Soc. Am. Mem. 79, 347–364 (1960)

  8. 8

    Hoskins, E. R. The failure of thick-walled hollow cylinders of isotropic rock. Int. J. Rock Mech. Min. Sci. 6, 99–125 (1969)

  9. 9

    Handin, J. On the Coulomb-Mohr failure criterion. J. Geophys. Res. 74, 5343–5348 (1969)

  10. 10

    Mogi, K. Effect of the intermediate principal stress on rock failure. J. Geophys. Res. 72, 5117–5131 (1967)

  11. 11

    Leon, A. Über die Rolle des Trennbruches im Rahmen der Mohrschen Anstrengungshypothese. Bauingenieur 15, 318–321 (1934)

  12. 12

    Nadai, A. Theory of Flow and Fracture of Solids (McGraw Hill, New York, 1934)

  13. 13

    Griffith, A. A. Theory of rupture. Proc. Int. Congr. Appl. Mech. 1, 55–63 (1924)

  14. 14

    McClintock, F. A. & Walsh, J. B. in Proc. 4th US Nat. Congr. Appl. Mech. Vol. II, 1015–1021 (Am. Soc. Mech. Eng., New York, 1962)

  15. 15

    Murrell, S. A. F. The effect of triaxial stress systems on the strength of rocks at atmospheric temperatures. Geophys. J. R. Astron. Soc. 10, 231–281 (1965)

  16. 16

    Murrell, S. A. F & Digby, P. J. The theory of brittle fracture initiation under triaxial stress conditions. I and II. Int. Geophys. J. R. Astron. Soc. 19, 309–334 and 499–512 (1970)

  17. 17

    Brace, W. F. An extension of the Griffith theory of fracture to rocks. J. Geophys. Res. 65, 3477–3480 (1960)

  18. 18

    Secor, D. T. Role of fluid pressure in jointing. Am. J. Sci. 263, 633–646 (1965)

  19. 19

    Brace, W. F. in State of Stress in the Earth's Crust (ed. Judd, W. R.) 111–180 (American Elsevier, New York, 1964)

  20. 20

    Schock, R. N. & Louis, H. Strain behavior of a granite and a greywacke sandstone in tension. J. Geophys. Res. 87, 7817–7823 (1982)

  21. 21

    Pieri, M., Burlini, L., Kunze, K., Stretton, I. & Olgaard, D. Rheological and microstructural evolution of Carrara marble with high shear strain: results from high temperature torsion experiments. J. Struct. Geol. 23, 1393–1413 (2001)

  22. 22

    Ramsey, J. M. Experimental Study of the Transition from Brittle Shear Fractures to Joints (Texas A&M Univ. Press, College Station, TX, 2003)

  23. 23

    Neuber, H. Theory of Notch Stresses (McGraw-Hill, New York, 1937)

  24. 24

    Handin, J., Friedman, M., Logan, J. M., Pattison, L. J. & Swolfs, H. S. in Flow and Fracture of Rocks (eds Heard, H. C., Borg, I. Y., Carter, N. L. & Raleigh, C. B.) 1–28 (AGU Geophys. Monogr. 16, American Geophysical Union, 1972)

  25. 25

    Jaeger, J. C. & Hoskins, E. R. Stresses and failure in rings of rock loaded in diametral tension or compression. Br. J. Appl. Phys. 17, 685–692 (1966)

  26. 26

    Engelder, T. The analysis of pinnate joints in the Mount Desert Island granite: implications for post-intrusion kinematics in the coastal volcanic belt, Maine. Geology 17, 564–567 (1989)

  27. 27

    Reches, Z. & Lockner, D. Nucleation and growth of faults in brittle rocks. J. Geophys. Res. 99, 18159–18174 (1994)

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We thank M. Finn, A. K. Kronenberg and J. S. Chester for discussions and suggestions, J. N. Magouirk and E. C. Powell for assistance in the laboratory, and J. S. Chester for reviews of the manuscript. This work was partially supported by US NSF.

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Correspondence to Frederick M. Chester.

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Figure 1: A representation using the Mohr diagram of the hypothesis that the brittle failure envelope and the transition from extension fracture to shear fracture is continuous.
Figure 2: Photographs of the undeformed and deformed notch-cut dog-bone samples of Carrara marble.
Figure 3: Fracture angle and fracture strength as a function of confining pressure.


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