Joints at high angles to normal fault strike: an explanation using 3-D numerical models of fault-perturbed stress fields

https://doi.org/10.1016/S0191-8141(99)00130-3Get rights and content

Abstract

Structural methods based on homogeneous stress states predict that joints growing in an extending crust form with strike orientations identical to normal faults. However, we document a field example where the strikes of genetically related normal faults and joints are almost mutually perpendicular. Field relationships allowed us to constrain the fracture sequence and tectonic environment for fault and joint growth. We hypothesize that fault slip can perturb the surrounding stress field in a manner that controls the orientations of induced secondary structures. Numerical models were used to examine the stress field around normal faults, taking into consideration the effects of 3-D fault shape, geometrical arrangement of overlapping faults, and a range of stress states. The calculated perturbed stress fields around model normal faults indicate that it is possible for joints to form at high angles to fault strike. Such joint growth may occur at the lateral tips of an isolated fault, but is most likely in a relay zone between overlapping faults. However, the angle between joints and faults is also influenced by the remote stress state, and is particularly sensitive to the ratio of fault-parallel to fault-perpendicular stress. As this ratio increases, joints can propagate away from faults at increasingly higher angles to fault strike. We conclude that the combined remote stress state and perturbed local stress field associated with overlapping fault geometries resulted in joint growth at high angles to normal fault strike at a field location in Arches National Park, Utah.

Introduction

Much of the understanding of joint orientations around normal faults follows from Anderson (1951), who indicated that opening mode cracks (specifically, dikes) should form parallel to the strikes of normal faults (perpendicular to the least compressive remote stress) (Fig. 1a). Although this assumption provides a rationale for predicting fault orientations in extending crust, it does not incorporate the stress perturbation induced by growing faults and the consequences of this for joint growth close to faults (Fig. 1b). The fact that faults perturb the surrounding stress field during slip events (Pollard and Segall, 1987; Barton and Zoback, 1994) has important consequences for the orientations of secondary structures such as smaller faults, joints, veins, and solution surfaces.

Geological observations have established that secondary structures can be induced in regions of increased stress around both opening mode (mode I) cracks, such as dikes (Delaney and Pollard, 1981; Delaney et al., 1986; Pollard and Segall, 1987; Rogers and Bird, 1987; Baer and Reches, 1991; Kattenhorn and Watkeys, 1995) and sliding mode (modes II and III) cracks, such as faults (Lajtai, 1969; Segall and Pollard, 1980, 1983; Rispoli, 1981; Cruikshank et al., 1991; Rawnsley et al., 1992; Homberg et al., 1997; Ohlmacher and Aydin, 1997; Willemse et al., 1997; Martel and Boger, 1998; Vermilye and Scholz, 1998). Laboratory experiments that record acoustic emission events in a sample undergoing shear failure also reveal microcrack development ahead of a propagating fault tip (Reches and Lockner, 1994).

If sufficient field evidence exists to suggest a genetic relationship between normal faults and spatially associated joints, joint orientations can perhaps be explained in the context of the fault-perturbed stress field. Joints act as paleostress indicators in rock and are assumed in this study to be mode I fractures that form perpendicular to the least compressive stress. Previous work on stress field heterogeneities around faults follows predominantly from field observations or modeling of either strike-slip or thrust faults (Barton and Zoback, 1994; Bürgmann et al., 1994; Roering et al., 1997). Our investigation focuses on the mechanics of stress perturbations by normal faulting and resultant joint development.

This study is motivated by observations of joints striking at high angles to normal faults in Arches National Park, Utah, in contrast to the predictions of Anderson (1951). First, the field example will be described to establish the connection between normal faults and joints. Second, we present three-dimensional mechanical analyses of the perturbed stress field in the vicinity of mechanically interacting, discontinuous normal faults. We then compare the numerical model results with field examples to demonstrate a similarity between model predictions and what is observed in nature, so as to provide a mechanical rationale for the field observations. Finally, we address implications of our model results for the analysis of deformation around normal faults in general and provide examples of applications.

Section snippets

Faults and joints in sandstone

Exceptional surface exposure in many regions in the Colorado Plateau physiographic province of the USA, such as Arches National Park in southeastern Utah (Fig. 2), provides ideal locations for the study of joints and faults in sandstone. Prominent exposure of Jurassic sandstones in this region has inspired a number of investigations of fault and joint characteristics (locations shown in Fig. 2). Dyer (1983, 1988) investigated systematic joint domains on both flanks of the Salt Valley anticline.

Numerical modeling

Field observations at Rocky Mesa are consistent with joint development being associated with faulting. We use numerical models to examine the stress field around idealized normal faults in order to investigate how joints might form in a fault-perturbed stress field. The 3-D numerical method addresses the effects of fault tipline shape and mechanical interaction of fault segments upon the numerical solution to the perturbed stress field. Using the underlying assumption that joints are opening

Discussion

Detailed field observations indicate that joints striking at high angles to normal faults at Rocky Mesa are related to the faulting. The state of stress during joint growth included fault-perpendicular tension induced by bending, lithostatic stresses, perturbation of the stress field by normal fault slip, regional tectonic stresses during and subsequent to the Laramide orogeny, and possibly internal fluid pressures in joints. Any hypothesis for the history of joint growth should reconcile this

Conclusions

Observations of normal fault and joint relationships in Arches National Park imply a genetic relationship between faulting and resultant joint development at high angles to fault strike. A numerical analysis of stress fields around normal faults at depth indicates that slip events perturb the stress field in the near-tip region (<1% of the fault length) in a complex and highly variable manner. At the upper tips of faults, high stress magnitudes result in joints that form with identical strikes

Supplementary data

Acknowledgements

Funding was provided by the U.S. Department of Energy, Grant No. DEFG03-94ER14462, and the Rock Fracture Project of Stanford University. We benefited from insightful discussions with Juliet Crider, Michele Cooke, Manuel Willemse, and Laurent Maerten. Sincere thanks to Thomas Roznovsky for providing assistance with field mapping. We acknowledge the National Park Service for their support of scientific research in the parks, particularly Karen McKinlay-Jones at Arches National Park. Finally, we

References (83)

  • S.A. Kattenhorn et al.

    Blunt-ended dyke segments

    Journal of Structural Geology

    (1995)
  • C.S. Mansfield et al.

    High resolution fault displacement mapping from three-dimensional seismic data: evidence for dip linkage during fault growth

    Journal of Structural Geology

    (1996)
  • S.J. Martel

    Effects of cohesive zones on small faults and implications for secondary fracturing and fault trace geometry

    Journal of Structural Geology

    (1997)
  • A.J. Nicol et al.

    The shapes, major axis orientations and displacement patterns of fault surfaces

    Journal of Structural Geology

    (1996)
  • D.D. Pollard et al.

    Theoretical displacements and stresses near fractures in rock: with applications to faults, joints, veins, dikes, and solution surfaces

  • K.D. Rawnsley et al.

    Joint development in perturbed stress fields near faults

    Journal of Structural Geology

    (1992)
  • R. Rispoli

    Stress fields about strike-slip faults inferred from stylolites and tension gashes

    Tectonophysics

    (1981)
  • T. Rives et al.

    Analogue simulation of natural orthogonal joint set formation in brittle varnish

    Journal of Structural Geology

    (1994)
  • R.D. Rogers et al.

    Fracture propagation associated with dike emplacement at the Skaergaard intrusion, East Greenland

    Journal of Structural Geology

    (1987)
  • E.J.M. Willemse et al.

    Three-dimensional analyses of slip distributions on normal fault arrays with consequences for fault scaling

    Journal of Structural Geology

    (1996)
  • E.J.M. Willemse et al.

    Nucleation and growth of strike-slip faults in limestones from Somerset, U.K

    Journal of Structural Geology

    (1997)
  • G. Zhao et al.

    Sequence of deformations recorded in joints and faults, Arches National Park, Utah

    Journal of Structural Geology

    (1992)
  • E.M. Anderson

    The Dynamics of Faulting

    (1951)
  • M. Antonellini et al.

    Effect of faulting on fluid flow in porous sandstones: petrophysical properties

    American Association of Petroleum Geologists Bulletin

    (1994)
  • M. Antonellini et al.

    Effect of faulting on fluid flow in porous sandstones: geometry and spatial distribution

    American Association of Petroleum Geologists Bulletin

    (1995)
  • M. Antonellini et al.

    Petrophysical study of faults in sandstone using petrographic image analysis and X-ray computerized tomography

    Pure and Applied Geophysics

    (1994)
  • A. Aydin et al.

    Development of faults as zones of deformation bands and as slip surfaces in sandstone

    Pure and Applied Geophysics

    (1978)
  • A. Aydin

    Small faults formed as deformation bands in sandstone

    Pure and Applied Geophysics

    (1978)
  • Baars, D.L., Doelling, H.H., 1987. Moab salt-intruded anticline, east-central Utah. Geological Society of America...
  • D.L. Baars et al.

    Tectonic evolution of the Paradox Basin, Utah and Colorado

  • G. Baer et al.

    Mechanics of emplacement and tectonic implications of the Ramon Dike Systems, Israel

    Journal of Geophysical Research

    (1991)
  • J.M. Barnett et al.

    Displacement geometry in the volume containing a single normal fault

    American Association of Petroleum Geologists Bulletin

    (1987)
  • C.A. Barton et al.

    Stress perturbations associated with active faults penetrated by boreholes: Possible evidence for near-complete stress drop and a new technique for stress magnitude measurement

    Journal of Geophysical Research

    (1994)
  • A.A. Becker

    The Boundary Element Method in Engineering

    (1992)
  • Z.T. Bieniawski

    Rock Mechanics Design in Mining and Tunneling

    (1984)
  • Cater, F.W., 1970. Geology of the salt anticline region in southwestern Colorado. United States Geological Survey...
  • M.A. Comninou et al.

    The angular dislocation in a half-space

    Journal of Elasticity

    (1975)
  • M.L. Cooke et al.

    Fracture propagation paths under mixed mode loading within rectangular blocks of polymethyl methacrylate

    Journal of Geophysical Research

    (1996)
  • M.L. Cooke

    Fracture localization along faults with spatially varying friction

    Journal of Geophysical Research

    (1997)
  • S.L. Crouch et al.

    Boundary Element Methods in Solid Mechanics

    (1983)
  • K.M. Cruikshank et al.

    Role of fracture localization in arch formation, Arches National Park, Utah

    Geological Society of America Bulletin

    (1994)
  • Cited by (139)

    • The role of fracture branching in the evolution of fracture networks: An outcrop study of the Jurassic Navajo Sandstone, southern Utah

      2022, Journal of Structural Geology
      Citation Excerpt :

      As fractures form in these damage zones, lithology, bed thickness, mechanical stratigraphy, pre-existing fractures, and the presence or absence of inter-layer slip impact their development (e.g., Price, 1959; Couples and Lewis, 1998; Cooke and Underwood, 2001; Nelson, 2001; Bergbauer and Pollard, 2004; Smart et al., 2009; McGinnis et al., 2015; Surpless and Wigginton, 2020). As normal fault segments propagate, the stress field adjacent to isolated or interacting faults is perturbed relative to the remote tectonic stress field, resulting in a range of possible fracture orientations and patterns (e.g., Price and Cosgrove, 1990; Rives et al., 1992; Kattenhorn et al., 2000). Based on numerical modeling and field data, Kattenhorn et al. (2000) showed that fractures can grow at high angles to a normal fault plane near the lateral tips of normal faults, and they also demonstrated that a perturbed stress field extends furthest from fault segments proximal the lateral fault tipline and within relay zones between normal fault segments.

    View all citing articles on Scopus

    Supplemental 3-D perspective color images of numerical model results may be viewed online at http://veo.elsevier.nl/sg/publish/831

    1

    Present address: Department of Geology and Geological Engineering, University of Idaho, Moscow, ID 83844, USA.

    View full text