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The early Laramide tectonic history and Proterozoic metamorphic history of the northeastern Colorado Front Range were examined using kinematic data from minor faults at 25 locations, and U-Th/He dating of apatite from 2 samples (3 unsuccessful) supported by optical petrography, X-ray maps and geothermometry. The role of strike-slip faulting in Laramide uplift of the eastern flank of the northern Front Range was analyzed through kinematic analysis of 97 minor (<100 m trace) faults. The dominant fault population was oriented approximately perpendicular to bedding, with lineations sub-parallel to bedding. Rotating bedding to horizontal showed these faults to have the pattern of a strike-slip conjugate set. Unfolded left-lateral faults have an average orientation of (287, 87N) with lineations to (287, 01); right-lateral faults have an orientation of (065, 88S) with lineations to (245, 00). The timing of motion on these faults postdates 98 Ma deposition of Dakota group sandstones, and predates the folds that rotated them (68 Ma from the age of synorogenic conglomerates). The conclusion is that strike-slip motion was active during the earliest Laramide. The principal strain axes from these faults, after rotation, give an average shortening axis orientation of (276, 03) and an average extension direction of (006, 02). The calculated shortening axis orientation is consistent with that of later Laramide deformation, supporting the hypothesis that strike-slip deformation occurred in the northeast Front Range during the earliest Laramide. Analysis of minor faults on part of the eastern flank of the northern Front Range shows that strike-slip faulting was a locally important deformation mechanism at the onset of the Laramide orogeny. Principal strain axis analysis suggests that the regional tectonic regime was one of east-west shortening and north-south extension prior to the onset of the main phase of Laramide deformation, at which time the regional strain field rotated to one of east-west shortening and vertical extension. Twenty-seven thin-sections of Big Thompson Canyon metapelites were petrologically characterized prior to selection for mineral separation and U-Th/He analysis of apatite. All samples show late high-temperature static recrystallization that has partially recovered prior fabrics. At high grades, sillimanite porphyroblasts overgrow all fabrics. X-ray maps and geothermometry were also conducted to enhance the characterization of the sample suite. Garnet-biotite phase equilibria indicate that initial prograde metamorphism took place at approximately 550 °C. Apatites separated from five of the twenty-seven samples analyzed in thin section were analyzed for U-Th/He thermochronometry. Three samples returned no plausible results; one sample returned one plausible age; and one sample returned three similar and plausible ages. Basement rocks cooled through the closure temperatures for helium and fission-tracks in apatite nearly simultaneously, at about 55 Ma. These temperatures, 40 and 60 °C respectively, correspond to depths of ~ 1.5 and 2.5 km. Laramide exhumation of the Northern Front Range was very rapid. Estimates of minimum magnitude of exhumation during Laramide time may need to be increased from ~2 km to ~3 km. / text

Thesis (M. Sc.)--University of Canterbury, 2004. / Typescript (photocopy). Includes transparent overlays. Includes bibliographical references (leaves 147-152). Also available via the World Wide Web.

Large earthquakes often exhibit complex slip distributions and occur along non-planar faults, resulting in variable stress changes throughout the fault region. To better discern the role of stress changes and fluid flow on aftershock sequences, we examine areas of enhanced and reduced mean stress along the structurally complex strike-slip faults that hosted the 1992 Landers, 2010 El-Mayor Cucapah, and 2016 Kumamoto earthquakes. We characterize the behavior of aftershock sequences with the Epidemic Type Aftershock-Sequence Model and use the Maximum Log Likelihood method to determine the optimal set of ETAS parameter values along each fault. This study indicates that extensional areas experience greater secondary aftershock triggering and a higher density of aftershocks directly following the mainshock, which could be attributed to fluid influx. However, our results also highlight some shortcomings of the ETAS model, including high parameter correlation, and influence of catalog size and magnitude cutoff on parameter estimations.

The North Canterbury tectonic setting involves the southward propagating margin of easterly strike-slip activity intersecting earlier thrust activity propagating east from the Alpine Fault. The resulting tectonics contain a variety of structures caused by the way these patterns overlap, creating complexities on the regional and individual feature scale. An unpublished map by Jongens et al. (1999) shows the Ashley-Loburn Fault System crossing the plains from the east connected with the Springfield Thrust Fault in the western margins, possibly the southern limit of the east-west trending strikeslip activity. Of note are two hill structures inferred to be affected by this fault system. View Hill to the west, is on the south side of this fault junction, and Starvation Hill further east, was shown lying on the north side of a left stepover restraining bend. During thrust uplift and simple tilting of the View Hill structure, at least two uplift events post date last Pleistocene aggradation accounting for variations in scarp morphology. Broad constraints on fault dip and the age of the displacement surface suggest that slip-rates are in the order of 0.5 mm/year. East from View Hill, the strike-slip fault was originally thought to curve northeast, around the southeast of Starvation Hill. But there is neither evidence of a scarp, nor other clear evidence of surface faulting at Starvation Hill, which poses the question of the extent to which folding may reflect both fault geometry and fault activity. Starvation Hill is a triangular shape, with a series of distinctive smooth, semi-planar surfaces, lapping across both sides of the hill at a range of elevations and gradients. These surfaces are thought to be remnants of old river channels, and are indicative of tilting and upwarping of the hill structure. 3D computer modelling of these surfaces, combined with studies of the cover sequence on the hill, resulted in inferences being drawn as to the location of hinge lines of a dual-hinged anticline and an overview of the tectonic history of the hill. This illustrates the potential to apply topographical and geomorphic studies to the evolution of geometrically complex structures Starvation Hill is interpreted to be the result of two fault-generated folds, one fault trending north, the other, more recent fault, trending east. These two faults are thought to be sequentially developed segments of the original fault zone inferred by Jongens et al. (1999) but with reinterpreted location and mechanism detail. The presence of two faults has resulted in overprinted differential uplift of the structure, which has been significantly degraded, especially in the southwest corner of the hill. The majority of the formation of the northerly trending structure of Starvation Hill is inferred to be pre-Otiran, with uplift of the later east trending structure continuing into the late Pleistocene and Holocene.

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, 2003. / Title from document title page. Document formatted into pages; contains vi, 21, [24] p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references (p. 20-21).

The North Canterbury tectonic setting involves the southward propagating margin of easterly strike-slip activity intersecting earlier thrust activity propagating east from the Alpine Fault. The resulting tectonics contain a variety of structures caused by the way these patterns overlap, creating complexities on the regional and individual feature scale. An unpublished map by Jongens et al. (1999) shows the Ashley-Loburn Fault System crossing the plains from the east connected with the Springfield Thrust Fault in the western margins, possibly the southern limit of the east-west trending strikeslip activity. Of note are two hill structures inferred to be affected by this fault system. View Hill to the west, is on the south side of this fault junction, and Starvation Hill further east, was shown lying on the north side of a left stepover restraining bend. During thrust uplift and simple tilting of the View Hill structure, at least two uplift events post date last Pleistocene aggradation accounting for variations in scarp morphology. Broad constraints on fault dip and the age of the displacement surface suggest that slip-rates are in the order of 0.5 mm/year. East from View Hill, the strike-slip fault was originally thought to curve northeast, around the southeast of Starvation Hill. But there is neither evidence of a scarp, nor other clear evidence of surface faulting at Starvation Hill, which poses the question of the extent to which folding may reflect both fault geometry and fault activity. Starvation Hill is a triangular shape, with a series of distinctive smooth, semi-planar surfaces, lapping across both sides of the hill at a range of elevations and gradients. These surfaces are thought to be remnants of old river channels, and are indicative of tilting and upwarping of the hill structure. 3D computer modelling of these surfaces, combined with studies of the cover sequence on the hill, resulted in inferences being drawn as to the location of hinge lines of a dual-hinged anticline and an overview of the tectonic history of the hill. This illustrates the potential to apply topographical and geomorphic studies to the evolution of geometrically complex structures Starvation Hill is interpreted to be the result of two fault-generated folds, one fault trending north, the other, more recent fault, trending east. These two faults are thought to be sequentially developed segments of the original fault zone inferred by Jongens et al. (1999) but with reinterpreted location and mechanism detail. The presence of two faults has resulted in overprinted differential uplift of the structure, which has been significantly degraded, especially in the southwest corner of the hill. The majority of the formation of the northerly trending structure of Starvation Hill is inferred to be pre-Otiran, with uplift of the later east trending structure continuing into the late Pleistocene and Holocene.

Thesis (M.S.)--University of Texas at El Paso, 2009. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.