Shears of the second order

McKinstry, Hugh Exton

doi:10.2475/ajs.251.6.401

Cited by 53 publications

(10 citation statements)

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“…Previous hypotheses on the origin of second-order structures along strike-slip faults can be divided inio two groups (order refers to the relative size of faults within the zone, whereas primary and secondary refer to the time relationships of the faults [Groshong and Rodgers, 1978]). These groups are as follows: (1) second-order structures are secondary features caused by slip on a strike-slip fault at the same structural level either as an end effect [Anderson, 1951;Chinnery, 1966] or along the whole length of the strike-slip fault [McKinstry, 1953;Moody and Hill, 1956]; (2) second-order structures are primary features that develop during the formation of a fault in originally unfaulted rock [ Tchalenko, 1970;Groshong and Rodgers, 1978]. The first group of hypotheses is based mainly on field observations and is consistent with the idea that earthquakes occur by slip on preexisting strike-slip fault planes.…”

Section: Neotectonic Significance Of Strike-slip Structuresmentioning

confidence: 99%

Neotectonics of the Caribbean

Mann¹,

Burke²

1984

Reviews of Geophysics

172

103

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A compilation of earthquake focal mechanism solutions together with the interpretation of inclined, intermediate-depth seismic zones, Neogene strike-slip faults, fault-controlled basins, and volcanism is used to test three existing models for the neotectonic (i.e., Neogene or post-Oligocene) development of the Caribbean. The current models, although based on different hypotheses using different data sets, are similar and suggest varying degrees of convergence between the Caribbean and either North or South American plates or convergence between the Caribbean plate and continental fragments of the northwestern corner of South America. Using model 1, previous workers have interpreted the disposition of fracture zones and magnetic anomalies in the central and South Atlantic as indicating that the Caribbean plate is being compressed by north-south convergence between the Americas with the result that it is being driven eastward relative to the Americas along strike-slip faults while producing east-west trending subductionlike convergent zones along northern and southern plate margins. Using model 2, previous workers have interpreted the azimuths of active strike-slip faults and focal mechanism solutions and closure of three-plate velocity circuits as indicating that the South American plate converges in a west-northwesterly direction on the southern margin of the Caribbean plate and has produced compressional features, while strike-slip motion dominates along the northern boundary. Using model 3, previous workers have interpreted focal mechanism solutions and the pattern of strike faulting and basin development in northwestern South America to suggest right-lateral displacement of the northwestern corner of South America relative to the craton with convergence and compression in the south central Caribbean. Our integration of geologic information on faults, basins, and volcanism considerably extends the limited record of plate interactions known from historical reports of the past few hundred years and recorded earthquakes and suggests that (1) relative motion between the North American and Caribbean plates is dominantly east-west strike-slip motion, although areas of complex internal deformation associated with restraining bend or compressional strike-slip fault segments have been identified in Jamaica, Hispaniola and Central America (2) relative motion between the South American and Caribbean plates is dominantly east-west strike-slip motion, although an area of restraining bend deformation has been identified in the Araya Peninsula of Venezuela; (3) relative motion between a triangular continental fragment of northwestern South America (the "Maracaibo Block") ranges from northwest to northeast along the south central margin of the Caribbean and appears to be driven mostly by the late Miocene-Pliocene collision of the Panama arc, although additional driving forces may include the collision of the Carnegie Ridge and/or oblique subduction (to the northeast) in Ecuador; and {4) relative motion (internal deformation) ...

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Section: Neotectonic Significance Of Strike-slip Structuresmentioning

confidence: 99%

Neotectonics of the Caribbean

Mann¹,

Burke²

1984

Reviews of Geophysics

172

103

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“…Anderson (1951), McKinstry (1953) and Moody and Hill (1956) have examined secondary shear features associated with faults and have developed the theory that movements within a main shear zone may rearrange the stresses in the immediate vicinity of the shear in such a way as to cause failure of the rock on a new set of complimentary fractures known as second order shears. This arrangement of stresses, therefore, produces only one set of monoclinal step-like folds similar to those known as kink-bands, or joint drags.…”

Section: Conjugate Fold Systemsmentioning

confidence: 99%

The Geometry of Conjugate Fold Systems

Ramsay

1962

Geol. Mag.

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Conjugate shear fold systems are often developed when brittle laminated rocks are subjected to stress. These structures may have an orthorhombic, monoclinic or triclinic symmetry depending upon the relationship of the principal axes of stress to the surface being folded. Within first order shear zones conjugate second order shear folds may be developed as a result of reorientation of the stress axes in these zones.The axes of both first and second order conjugate shear folds may form at any angle to the principal stress axes and to the direction of movement within the shear zones. The principal axes of stress are most reliably determined from the orientation of the axial planes of the first order conjugate folds.

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“…4). They also occur in discussion of secondary faulting (McKinstry, 1953;Lajtai, 1969). It appears subsequently that, for sliding surfaces, microfractures in these directions can be seen (cf.…”

Section: Introductionmentioning

confidence: 97%

Friction of Rocks and Stability of Rock Slopes

Jaeger

1971

Géotechnique

303

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Synopsis The similarities and differences between soil and rock mechanics are discussed with particular reference to the stability of slopes. The effects of constraints and of the stiffness of the system applying stress are of greater importance in rock mechanics. The criteria for failure of rocks are mostly empirical and lead to linear or power laws. Similar laws might be expected to hold for friction. While the Coulomb law is in general adequate for soils, it appears that the frictional behaviour of rocks is described better by a non-linear law and if a Coulomb law is used factors of safety are sensitive to the value adopted for the cohesion. The various methods for measuring friction are described and their limitations discussed. The process of wear and the area of contact between sliding surfaces are considered. It appears that in some cases residual values of friction are attained after small amounts of sliding. Gouge is built up during sliding and its behaviour appears to be time-dependent. At present, numerical values for friction and other parameters of jointed systems are uncertain and so simple formulae are still useful. A number of formulae for factors of safety for sliding on one or two plane surfaces are given. For the case of rock with closely spaced joints the use of soil mechanics theory for circular and other surfaces of sliding is reasonable. In this case, values of friction obtained from single joint surfaces or crushed rock are conservative since the interlocking of rock elements may cause a substantial increase in strength. Les similitudes et les différences entre la mécanique des sols et la mécanique des roches sont tuditudiées, avec réference particulière à la stabilité des pentes. Les effets des contraintes et de la rigidité du systéme appliquant les contraintes ont plus d'importance dans la mécanique des roches. Les critères pour la rupture des roches sont pour la plupart empiriques, et suggeèent des lois lintudiaires ou de puissance. On peut supposer des lois similaires pour le frottement. Alors que la loi de Coulomb est gènèralement correcte en ce qui concerne les sols, il semble que le frottement des roches serait plus correctement dtudi;fini par une loi non linéaire, et si l'on applique une loi de Coulomb les facteurs de sécurité sont affectés par la valeur adoptée pour la coh´esion. Les différentes methodes de mesure du frottement sont décrites, et leur champ d'application est étudié. On tient compte également du processus d'usure et de la superficie de contact entre les surfaces en glissement. 11 semble que dans certains cas on obtienne des valeurs résiduelles de frottement aprés des glissements de faible importance. Des cavités se produisent pendant le glissement et leur comportement semble dépendre d'un facteur temps. Actuellement, les valeurs numériques de glissement et les autres paramétres des systémes joints ne sont pas certains, et une formule aussi simple rend encore de grands services. On donne un certain nombre de formules pour les facteurs de sécurité du glissement pour une ou deux surfaces planes. Pour les roches avec des joints rapprochés on peut utiliser la théorie de mécanique des sols pour les surfaces de glissement circulaires et autres. Dans ce cas, les valeurs de frottement obtenues pour les surfaces à joint unique ou les roches écrasées sont plutôt en deçà de la vérité puisque l'enchevêtrement des roches peut résulter en unimportant accroissement de la solidité.

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Shears of the second order

Cited by 53 publications

References 0 publications

Neotectonics of the Caribbean

Neotectonics of the Caribbean

The Geometry of Conjugate Fold Systems

Friction of Rocks and Stability of Rock Slopes

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