Fault (geology)

About: Fault (geology) is a(n) research topic. Over the lifetime, 26732 publication(s) have been published within this topic receiving 744535 citation(s).

The Mechanics of Earthquakes and Faulting

Abstract: This essential reference for graduate students and researchers provides a unified treatment of earthquakes and faulting as two aspects of brittle tectonics at different timescales. The intimate connection between the two is manifested in their scaling laws and populations, which evolve from fracture growth and interactions between fractures. The connection between faults and the seismicity generated is governed by the rate and state dependent friction laws - producing distinctive seismic styles of faulting and a gamut of earthquake phenomena including aftershocks, afterslip, earthquake triggering, and slow slip events. The third edition of this classic treatise presents a wealth of new topics and new observations. These include slow earthquake phenomena; friction of phyllosilicates, and at high sliding velocities; fault structures; relative roles of strong and seismogenic versus weak and creeping faults; dynamic triggering of earthquakes; oceanic earthquakes; megathrust earthquakes in subduction zones; deep earthquakes; and new observations of earthquake precursory phenomena.

Propagating extrusion tectonics in Asia: New insights from simple experiments with plasticine

Abstract: Plane indentation experiments on unilaterally confined blocks of plasticine help us to understand finite intracontinental deformation and the evolution of strike-slip faulting in eastern Asia. Several large left-lateral strike-slip faults may have been activated successively, essentially one at a time. The experiments suggest that the penetration of India into Asia has rotated (≈25°) and extruded (≈800 km) Indochina to the southeast along the then left-lateral Red River fault in the first 20 to 30 m.y. of the collision. This process can account for the opening of the South China Sea before late Miocene time. Extrusion tectonics then migrated north, activating the Altyn Tagh fault as a second major left-lateral fault and moving southern China hundreds of kilometres to the east. As this occurred, Indochina kept rotating clockwise (as much as 40°), but the sense of motion reversed on the Red River and other strike-slip faults in the south. Opening of the Mergui basin and Andaman Sea (up to the present) also appears to be a simple kinematic consequence of the extrusion. Recent rifts in northeastern China and Yunnan may be considered incipient analogs of the South China and Andaman Seas. Other Tertiary tectonic features such as the sedimentary basins of the Gulf of Thailand may be explained as collisional effects, if one uses our experiments as a guide. The experiments also suggest that a major left-lateral strike-slip fault and rift system will propagate across the Tien Shan, Mongolia, and Baikal to the Sea of Okhotsk.

Fault zone architecture and permeability structure

Abstract: Fault zone architecture and related permeability structures form primary controls on fluid flow in upper-crustal, brittle fault zones. We develop qualitative and quantitative schemes for evaluating fault-related permeability structures by using results of field investigations, laboratory permeability measurements, and numerical models offlow within andnearfaultzones.Thequalitativeschemecomparesthepercentageofthetotalfaultzone width composed of fault core materials (e.g., anastomosing slip surfaces, clay-rich gouge, cataclasite,andfaultbreccias)tothepercentageofsubsidiarydamagezonestructures(e.g., kinematically related fracture sets, small faults, and veins). A more quantitative scheme is developed to define a set of indices that characterize fault zone architecture and spatial variability.Thefaultcoreanddamagezonearedistinctstructuralandhydrogeologicunits that reflect the material properties and deformation conditions within a fault zone. Whether a fault zone will act as a conduit, barrier, or combined conduit-barrier system is controlled by the relative percentage of fault core and damage zone structures and the inherent variability in grain scale and fracture permeability. This paper outlines a frameworkforunderstanding,comparing,andcorrelatingthefluidflowpropertiesoffaultzones in various geologic settings.

Fault rocks and fault mechanisms

Abstract: Physical factors likely to affect the genesis of the various fault rocks—frictional properties, temperature, effective stress normal to the fault and differential stress—are examined in relation to the energy budget of fault zones, the main velocity modes of faulting and the type of faulting, whether thrust, wrench, or normal. In a conceptual model of a major fault zone cutting crystalline quartzo-feldspathic crust, a zone of elastico-frictional (EF) behaviour generating random-fabric fault rocks (gouge—breccia—cataclasite series—pseudotachylyte) overlies a region where quasi-plastic (QP) processes of rock deformation operate in ductile shear zones with the production of mylonite series rocks possessing strong tectonite fabrics. In some cases, fault rocks developed by transient seismic faulting can be distinguished from those generated by slow aseismic shear. Random-fabric fault rocks may form as a result of seismic faulting within the ductile shear zones from time to time, but tend to be obliterated by continued shearing. Resistance to shear within the fault zone reaches a peak value (greatest for thrusts and least for normal faults) around the EF/QP transition level, which for normal geothermal gradients and an adequate supply of water, occurs at depths of 10–15 km.

Geologically current plate motions

Abstract: SUMMARY We describe best-fitting angular velocities and MORVEL, a new closure-enforced set of angular velocities for the geologically current motions of 25 tectonic plates that collectively occupy 97 per cent of Earth's surface. Seafloor spreading rates and fault azimuths are used to determine the motions of 19 plates bordered by mid-ocean ridges, including all the major plates. Six smaller plates with little or no connection to the mid-ocean ridges are linked to MORVEL with GPS station velocities and azimuthal data. By design, almost no kinematic information is exchanged between the geologically determined and geodetically constrained subsets of the global circuit—MORVEL thus averages motion over geological intervals for all the major plates. Plate geometry changes relative to NUVEL-1A include the incorporation of Nubia, Lwandle and Somalia plates for the former Africa plate, Capricorn, Australia and Macquarie plates for the former Australia plate, and Sur and South America plates for the former South America plate. MORVEL also includes Amur, Philippine Sea, Sundaland and Yangtze plates, making it more useful than NUVEL-1A for studies of deformation in Asia and the western Pacific. Seafloor spreading rates are estimated over the past 0.78 Myr for intermediate and fast spreading centres and since 3.16 Ma for slow and ultraslow spreading centres. Rates are adjusted downward by 0.6–2.6 mm yr−1 to compensate for the several kilometre width of magnetic reversal zones. Nearly all the NUVEL-1A angular velocities differ significantly from the MORVEL angular velocities. The many new data, revised plate geometries, and correction for outward displacement thus significantly modify our knowledge of geologically current plate motions. MORVEL indicates significantly slower 0.78-Myr-average motion across the Nazca–Antarctic and Nazca–Pacific boundaries than does NUVEL-1A, consistent with a progressive slowdown in the eastward component of Nazca plate motion since 3.16 Ma. It also indicates that motions across the Caribbean–North America and Caribbean–South America plate boundaries are twice as fast as given by NUVEL-1A. Summed, least-squares differences between angular velocities estimated from GPS and those for MORVEL, NUVEL-1 and NUVEL-1A are, respectively, 260 per cent larger for NUVEL-1 and 50 per cent larger for NUVEL-1A than for MORVEL, suggesting that MORVEL more accurately describes historically current plate motions. Significant differences between geological and GPS estimates of Nazca plate motion and Arabia–Eurasia and India–Eurasia motion are reduced but not eliminated when using MORVEL instead of NUVEL-1A, possibly indicating that changes have occurred in those plate motions since 3.16 Ma. The MORVEL and GPS estimates of Pacific–North America plate motion in western North America differ by only 2.6 ± 1.7 mm yr−1, ≈25 per cent smaller than for NUVEL-1A. The remaining difference for this plate pair, assuming there are no unrecognized systematic errors and no measurable change in Pacific–North America motion over the past 1–3 Myr, indicates deformation of one or more plates in the global circuit. Tests for closure of six three-plate circuits indicate that two, Pacific–Cocos–Nazca and Sur–Nubia–Antarctic, fail closure, with respective linear velocities of non-closure of 14 ± 5 and 3 ± 1 mm yr−1 (95 per cent confidence limits) at their triple junctions. We conclude that the rigid plate approximation continues to be tremendously useful, but—absent any unrecognized systematic errors—the plates deform measurably, possibly by thermal contraction and wide plate boundaries with deformation rates near or beneath the level of noise in plate kinematic data.