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Rock creep mechanics
Published in Xia-Ting Feng, Rock Mechanics and Engineering, 2017
Defects can also be linear or planar, as in dislocations (Davis & Reynolds, 1996). Under differential stress, atoms will jump from one site to another until the full array of atoms is shifted. Depending on the pressure and the temperature conditions, different creep mechanisms will occur (Figure 5). These range from dissolution creep, for low temperature and moderate differential stress, to diffusion creep for higher temperatures. When differential stress is elevated, dislocation creep will be the predominant mechanism leading to fracture and the production of cataclasite. This phenomenon could be advantageously described using dislocation mechanics (McClintock & Argon, 1966). Additionally, movement at the grain boundaries can also occur.
Metamorphic rocks
Published in W.S. MacKenzie, A.E. Adams, K.H. Brodie, Rocks and Minerals in Thin Section, 2017
W.S. MacKenzie, A.E. Adams, K.H. Brodie
A cataclasite is a rock intensely deformed at low temperature by processes involving brittle fracturing and frictional sliding between the fragments. Cataclasis is often localized into fault zones but can be widely distributed. The rock can be cohesive, with a poorly developed or absent schistosity or foliation, or can be incohesive, characterised by generally angular porphyroclasts and rock fragments in a finer-grained matrix of similar composition. Cohesive cataclasites are usually held together either by a cement phase deposited from solution or by clay minerals if present in sufficient proportions. Cataclasites in fault zones are commonly termed fault gouge and are often quite well foliated or banded. Coarse grained cataclasites are often called a breccia.
Metamorphic Rocks
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
Dislocation metamorphism occurs on faults and thrusts where rock is altered by earth movement (see Figs 1.20 and 2.3). Much energy stored in the surrounding crust is released along these zones and dislocation metamorphism is associated with earthquakes (Chapter 1). Within 10 km of the Earth’s surface these movements involve brittle fracture of rock, the mechanical breaking caused by shearing, grinding and crushing being termed brecciation or cataclasis (= breaking down). Major shear zones continue to great depths and below 10 km pressure and temperature may be sufficient for dislocation to occur by plastic deformation. Fine-grained rocks are produced, called mylonites (Greek, mylon = mill).
Numerical Modeling of Reverse Fault Rupture and Its Impact on Mountain Tunnels
Published in Journal of Earthquake Engineering, 2023
Zhen Wang, Mi Zhao, Jingqi Huang, Zilan Zhong, Xiuli Du
The second component specifies the energy dissipated during failure. The energy dissipated by the damage process is termed as fracture energy (Gf) and equal to the area under the cohesive law, as shown in Fig. 5. The fracture energy of fault rocks varies with lithology. Bazant and Kazemi (1990) reported that Gf for different types of rocks ranges between tens to hundreds of newtons per meter. The fault rocks in region affected by the damage zone primarily consist of limestone, basalt, cataclasite, and fault breccia. Their strength and elastic modulus are lower than that of intact rock. In this numerical study, the fracture energy actually represents the energy required for the destruction of the cohesive element, used to simulate the fault core. Owing to the poor petrophysical properties of the rock masses in the fault core, Gf was assumed as 5–50 N/m for the parametric study.
Past large earthquakes on the Alpine Fault: paleoseismological progress and future directions
Published in New Zealand Journal of Geology and Geophysics, 2018
Jamie D. Howarth, Ursula A. Cochran, Robert M. Langridge, Kate Clark, Sean J. Fitzsimons, Kelvin Berryman, Pilar Villamor, Delia T. Strong
The Alpine Fault is the boundary between the Pacific and Australian plates in southern New Zealand. The fault is a transform structure joining the opposing Hikurangi and Puysegur subduction zones and represents significant localisation of strain (Norris and Cooper 2007). The Alpine Fault was first recognised by Wellman and Willett (1942) and in 1949 Wellman presented the offset of the Dun Mountain Ophiolite Belt Terrane to argue for 480 km of dextral displacement on the fault. At the first order, the Alpine Fault is a remarkably straight feature that strikes at c. 055° transecting the western South Island. Slip on the fault is oblique along its length with varying components of dextral strike-slip and reverse dip-slip that is typically accommodated in a narrow < 50 m zone of fault gouge and cataclasite (Norris and Cooper 2007).
Geomechanical characterisation of discontinuous greywacke from the Wellington region based on laboratory testing
Published in New Zealand Journal of Geology and Geophysics, 2022
Marc-André Brideau, Christopher I. Massey, Jonathan M. Carey, Barbara Lyndsell
UCS and Brazilian test results for the cataclasite unit of the Wellington region greywacke are reported in this paper for the first time. In total 6 UCS and 2 Brazilian tests were conducted on samples from one borehole located along State Highway 2 northeast of the Ngauranga interchange with State Highway 1. The results appear to indicate that cataclasite is at the lower end of the UCS and Brazilian range of results for both sandstone and mudstone, even when slightly weathered (Figures 7A and 13A). Figure 3B shows that the cataclasite has a dominant fabric. Plotting the UCS values as a function of the angle between fabric and the core axis suggest that there is a strength anisotropy in the cataclasite samples (Figure 14).