Academic literature on the topic 'Faults (geology)'

Thesis (Ph.D.) - University of Glasgow, 2008.<br>Ph.D. thesis submitted to the Department of Geographical and Earth Sciences, Faculty of Physical Sciences, University of Glasgow, 2008. Includes bibliographical references. Print version also available.

Late Pleistocene displacement along the Lone Mountain fault suggests the Silver Peak-Lone Mountain (SPLM) extensional complex is an important structure in accommodating and transferring strain within the eastern California shear zone (ECSZ) and Walker Lane. Using geologic and geomorphic mapping, differential global positioning system surveys, and terrestrial cosmogenic nuclide (TCN) geochronology, we determined rates of extension across the Lone Mountain fault in western Nevada. The Lone Mountain fault is the northeastern component of the SPLM extensional complex, and is characterized by a series of down-to-the-northwest normal faults that offset the northwestern Lone Mountain and Weepah Hills piedmonts. We mapped eight distinct alluvial fan deposits and dated three of the surfaces using ¹⁰BE TCN geochronology, yielding ages of 16.5 +/- 1.2 ka, 92.3 +/- 8.6 ka, and 142.2 +/- 19.5 ka for the Q3b, Q2c, and Q2b deposits, respectively. The ages were combined with scarp profile measurements across the displaced fans to obtain minimum rates of extension; the Q2b and Q2c surfaces yield an extension rate between 0.1 +/- 0.1 and 0.2 +/- 01 mm/yr and the Q3b surface yields a rate of 0.2 +/-.1 to 0.4 +/- 0.1 mm/yr, depending on the dip of the fault. Active extension on the Lone Mountain fault suggests that it helps partition strain off of the major strike-slip faults in the northern ECSZ and transfers deformation around the Mina Deflection northward into the Walker Lane. Combining our results with estimates from other faults accommodating dextral shear in the northern ECSZ reveals an apparent discrepancy between short- and long-term rates of strain accumulation and release. If strain rates have remained constant since the late Pleistocene, this could reflect transient strain accumulation, similar to the Mojave segment of the ECSZ. However, our data also suggest an increase in strain rates between ~92 ka and ~17 ka, and possibly to present day, which may also help explain the mismatch between long- and short-term rates of deformation in the region.

Thesis (M.S.)--West Virginia University, 2008.<br>Title from document title page. Document formatted into pages; contains vii, 84 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references (p. 75-78).

Thesis (Ph. D.)--Dept. of Geosciences and School of Computing and Engineering. University of Missouri--Kansas City, 2005.<br>"A dissertation in geosciences and computer networking." Advisor: Tina M. Niemi. Typescript. Vita. Description based on contents viewed Mar. 12, 2007; title from "catalog record" of the print edition. Includes bibliographical references (leaves 331-341). Online version of the print edition.

<p> The activity of the Ereen Uul fault and the Sanglin Dalai Nurr fault in central Mongolia has not been studied in detail. The Erren Uul fault is a normal fault located 45 km southeast from Harhorin and the Sanglin Dalai Nurr fault is a right-lateral strike-slip fault located 30 km south of Harhorin next to the Hangay Mountains. Remote sensing and field observations were used to refine a map by the Mongolian Geologic Survey at a scale of 1:1,000,000 to a scale of 1:100,000. This new map covers an area of 8,072 km². The basin asymmetry factor, stream length-gradient index, and hypsometric curves were developed for basins adjacent to these faults. These geomorphic indices along with the refined map were used to conclude that the Ereen Uul and Sanglin Dalai Nurr faults are active.</p>

This research is an investigation into two different aspects of the faulting process. The first part of the study focuses on the initial stages of fault formation, while the second analyzes the deformation produced by an existing fault. The section on fault formation is an attempt to determine whether slip on an existing fault has a significant effect on the formation of subsequent faults. A two-dimensional elastic finite element technique is used to examine the system of stresses produced by slip on an initial fault, assuming that deformation occurs either elastically or by brittle failure. A Mohr-Coulomb failure criterion is used to determine the most likely region of secondary fault initiation. A strain energy criterion is then used to find the preferred direction of fault propagation. The study on fault formation is subdivided into two sections representing two idealized tectonic environments: purely extensional and purely compressional. The section on extensional fault formation explains the prevalence of grabens in extensional tectonic regimes as a consequence of the stress perturbations due to slip on an initial normal fault. Slip on the initial fault produces a region of high proximity to failure at the surface of the downthrown block. A secondary fault would be expected to initiate in this region. The direction of propagation of this fault that most effectively relieves the shear stress (and therefore minimizes the total strain energy) is toward the initial fault, resulting in an antithetic orientation, or graben. The width of the graben is found to be controlled by the depth of the initial normal fault, rather than the depth to a change in material properties. The study of compressional fault formation indicates that, except for steeply-dipping faults, the presence of an initial thrust fault tends to suppress the formation of other faults in its vicinity. However, if a secondary fault initiates near an initial thrust fault, the direction in which it propagates will be influenced by the presence of the initial fault. The way in which it is influenced is dependent on the fault dip. The final part of this study examines the deformation produced by repeated earthquake cycles on the San Andreas fault in southern California. A three-dimensional, time-dependent kinematic finite element model is used to investigate the influence of slip distribution and rheological parameters on the predicted horizontal and vertical deformation. The models include depth-varying rheological properties and power-law viscoelastic behavior. The predicted deformation patterns are fairly sensitive to the parameters used in this study. Of particular importance is the calculation of vertical uplift rate since, in many cases, models that cannot be distinguished from each other on the basis of horizontal deformation may produce distinctive vertical uplift patterns.

Seismic-scale faults are generally associated with clusters of subresolution faults, and the issue of how to predict the latter's numbers and distribution has been the subject of much recent debate due to its bearing on accurate fault seal evalution. One important class of subseismic-scale faults are deformation bands, which are tabular shear zones commonly formed in reservoir-quality aeolian and fluvial sandstone successions. Relevant outcrop and oil field case studies suggest such structures can reduce host rock permeability by up to four orders of magnitude, yet there is little published infonnation on the controls on their localisation and their relationship to larger-scale fault growth processes. This study addresses this knowledge gap and reports results of integrated structural, statistical, probe permeability and hydromechanical test investigations on fault-controlled deformation band arrays from two areas, Cullercoats Bay in NE England and the Clair Field, offshore NW UK continental shelf. Key aims are to examine the mesoand microscopic architecture of these band networks, establish their general evolution and elucidate their relationship to large fault development. Ancillary concerns include the expansion of the still limited database of deformation band spatial attributes, and assessment of the main areas of sensitivity in the analytical and statistical techniques used to describe these and other similar fault systems. Deformation bands at Cullercoats occur within the aeolian Yellow Sands of Permian age in the hanging wall of the Ninety Fathom fault, a major normal fault episodically active from the Carboniferous until at least Permian times. Structural analysis suggests that this band population was initiated as a result of dextral or oblique-dextral slip on the underlying Carboniferous Ninety Fathom fault, and was then progressively modified during the propagation of this fault into the overlying sediment cover and attendant development of fault-related folding and second-order faulting. In Clair, deformation bands are associated with arrays of calcite-filled veins and are inferred to have formed in response to fault-triggered fluid redistribution processes within the variably lithified aeolian-fluvial sandstones of the Clair Group. Statistical and mechanical evidence from both areas indicates that deformation band growth preceded major fault formation there, a finding that is consistent with the predictions of post-yield fracture mechanics models for process zone development at fault tips. A further common result from the two localities is that deformation band development and permeability character appears to be primarily controlled by the porosity and loading history of the faulted sandstones; therefore, assessment of the time of faulting should be a first step for determining whether a given subsurface fault is likely to be associated with deformation bands. Specific conclusions are: (1) The damage zones of band-related faults in porous sandstones scale linearly with fault displacement. (2) Deformation band densities decay quasi-exponentially with increasing distance from the faults within whose damage zones they occur. (3) Deformation band spacing distributions depart from strict self-similarity owing to the confinement of the bands within discrete mechanical horizons, yet their overall statistical character attests to multifractal scaling and Levytype stable behaviour. (4) Because of the observed deviations of deformation band statistics from simple power-law scaling laws, extrapolation of seismic-scale fault populations down to the deformation band level may give incorrect estimates of band numbers and/or size attributes. (5) Deformation bands display a broad range of microstructures and permeability signatures depending on host rock lithology, degree of compaction, previous stress history and local deformation details. (6) Despite their low-very low static permeabilities, deformation bands may act as fluid pathways during their development or reactivation in a subsequent tectonic event. (7) Application of standard statistical and probe permeability approaches to deformation band characterisation should be approached with caution due to problems inherent in the nature of deformation band systems itself. (8) Based on microstructural evidence and diagenetic and mechanical considerations deformation in the two study areas may have taken place at - 1.5-2 km, under maximum effective confining pressures of around 30 MPa.