Oceanic ridges and transform faults: Their intersection angles and resistance to plate motion

doi:10.1016/0012-821X(72)90051-9

Earth and Planetary Science Letters

Volume 15, Issue 2, June 1972, Pages 116-122

https://doi.org/10.1016/0012-821X(72)90051-9 Get rights and content

Abstract

The persistent near-orthogonal pattern formed by oceanic ridges and transform faults defies explanation in terms of rigid plates because it probably depends on the energy associated with deformation. For passive spreading, it is likely that the ridges and transforms adjust to a configuration offering minimum resistance to plate separation. This leads to a simple geometric model which yields conditions for the occurrence of transform faults and an aid to interpretation of structural patterns in the sea floor. Under reasonable assumptions, it is much more difficult for diverging plates to spread a kilometer of ridge than to slip a kilometer of transform fault, and the patterns observed at spreading centers might extend to lithospheric depths. Under these conditions, the resisting force at spreading centers could play a significant role in the dynamics of plate-tectonic systems.

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The Role of Fault-Zone Drilling
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The objective of fault-zone drilling projects is to directly study the physical and chemical processes that control deformation and earthquake generation within active fault zones. An enormous amount of field, laboratory, and theoretical work has been directed toward the mechanical and hydrological behavior of faults over the past several decades. Nonetheless, it is currently impossible to differentiate between – or even adequately constrain – the numerous conceptual models of active faults proposed over the years. For this reason, the Earth science community is left in the untenable position of having no generally accepted paradigm for the mechanical behavior of faults at depth. One of the primary causes for this dilemma is the difficulty of either directly observing or inferring physical properties and deformation mechanisms along faults at depth, as well as the need to observe directly key parameters such as the state of stress acting on faults at depth, pore fluid pressure (and its possible variation in space and time), and processes associated with earthquake nucleation and rupture. Today, we know very little about the composition of active faults at depth, their constitutive properties, the state of in situ stress or pore pressure within fault zones, the origin of fault-zone pore fluids, or the nature and significance of time-dependent fault-zone processes.
Is the Earth Lazy? A review of work minimization in fault evolution
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Citation Excerpt :
In this application, analytical solutions characterizing the system were solved to find the fault network that uses the least force to accommodate the prescribed plate boundary displacements via viscous flow within the fault zones. Lachenbruch and Thompson (1972) showed that minimum viscous dissipation predicts the orthogonal orientation of ridges and transform faults. This study was followed by several others that augmented this analysis to successfully account for various observations of ocean ridge geometry (Fig. 3) (e.g. Froidevaux, 1973; Stein, 1978; Kleinrock and Morgan, 1988).
The principle of work minimization has been used in various forms to account for the development of active fault systems within a wide range of tectonic settings. We review the successes, challenges and implications learned from previous applications of work minimization. Examination of the energy budget provides insight into the competing influences of different processes within fault systems at a variety of scales. We present each work budget component with considerations for numerical implementation. Additionally, we demonstrate numerical implementation by solving for the energy budgets and finding the most efficient propagation paths of a joint and several faults. Consideration of the energy budget captures growth patterns that are consistent with both laboratory observations and theoretical predictions using the energy release rate, G. Unlike using G, work minimization is not limited to collinear growth. In comparison with predictions using Coulomb failure planes, work minimization eliminates uncertainty in predicting fault propagation by (1) evaluating the trade-off between tensile and shear failure ahead of the fault and (2) avoiding the ambiguity introduced by the two potential Coulomb failure planes. Application of work minimization to faulting demonstrates the effectiveness of this approach in predicting both the orientation and timing of fault propagation.
Transform faults orthogonal to rifts: Insights from fully gravitational physical experiments
2012, Tectonophysics
Citation Excerpt :
It has been recognized that the orthogonal configuration is not required by the geometry of moving rigid blocks, but seems to be an intrinsic characteristic of the spreading phenomenon (Menard and Atwater, 1968) and a minimum-work configuration (Vogt et al., 1969). For passive spreading, it is likely that the ridges and transforms adjust to a configuration offering minimum resistance to plate separation; if a stable configuration exists, it represents a minimum energy configuration of some sort (Lachenbruch and Thompson, 1972). Therefore we investigated properties of the lithosphere and minimum-work, stable configurations that are constrained by conditions of mechanical and thermodynamic stability.
On the one hand, it is not yet understood why transform faults commonly form orthogonal to rifts, because this cannot be explained by simple theories of fracture mechanics. On the other hand, rock experimental data have shown that a very strong layer (elastic core) should exist between brittle and ductile layers of the lithosphere. Therefore, we investigated the influence of an elastic core on the generation of a transform fault/rift orthogonal configuration. We used fully gravitational scaled physical experiments of brittle-viscous models, and the results indicate that the elastic core and localized heat flow can be responsible for the observed common pattern of transforms orthogonal to rifts.
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The objective of fault-zone drilling projects is to directly study the physical and chemical processes that control deformation and earthquake generation within active fault zones. An enormous amount of field, laboratory, and theoretical work has been directed toward the mechanical and hydrological behavior of faults over the past several decades. Nonetheless, it is currently impossible to differentiate between – or even adequately constrain – the numerous conceptual models of active faults proposed over the years. For this reason, the Earth science community is left in the untenable position of having no generally accepted paradigm for the mechanical behavior of faults at depth. One of the primary causes for this dilemma is the difficulty of either directly observing or inferring physical properties and deformation mechanisms along faults at depth, as well as the need to observe directly key parameters such as the state of stress acting on faults at depth, pore fluid pressure (and its possible variation in space and time), and processes associated with earthquake nucleation and rupture. Today, we know very little about the composition of active faults at depth, their constitutive properties, the state of in situ stress or pore pressure within fault zones, the origin of fault-zone pore fluids, or the nature and significance of time-dependent fault-zone processes.
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The objective of fault-zone drilling projects is to directly study the physical and chemical processes that control deformation and earthquake generation within active fault zones. An enormous amount of field, laboratory, and theoretical work has been directed toward the mechanical and hydrological behavior of faults over the past several decades. Nonetheless, it is currently impossible to differentiate between – or even adequately constrain – the numerous conceptual models of active faults proposed over the years. For this reason, the Earth science community is left in the untenable position of having no generally accepted paradigm for the mechanical behavior of faults at depth. One of the primary causes for this dilemma is the difficulty of either directly observing or inferring physical properties and deformation mechanisms along faults at depth, as well as the need to observe directly key parameters such as the state of stress acting on faults at depth, pore fluid pressure (and its possible variation in space and time), and processes associated with earthquake nucleation and rupture. Today, we know very little about the composition of active faults at depth, their constitutive properties, the state of in situ stress or pore pressure within fault zones, the origin of fault-zone pore fluids, or the nature and significance of time-dependent fault-zone processes.

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Oceanic ridges and transform faults: Their intersection angles and resistance to plate motion

Abstract

Tectonophysics

Rises, trenches, great faults, and crustal blocks

J. Geophys. Res.

Fracture zones

Earth Sciences: Geophysics

A new class of faults and their bearing on continental drift

Nature

Changes in direction of sea floor spreading

Nature

Sensitivity of heat flow and gravity to the mechanism of sea floor spreading

J. Geophys. Res.

New interpretation of the geology of Iceland

Geol. Soc. Am. Bull.

Asthenosphere motions recorded by the ocean floor south of Iceland

EOS Trans. Am. Geophys. Un.