acase@tulane.edu / Fault growth is often accomplished by linking a series of en echelon faults through relay ramps. A relay ramp is the area between two overlapping fault segments that tilts and deforms as the faults accrue displacement. The structural evolution of breached normal fault relay ramps remains poorly understood because of the difficulty in defining how slip is partitioned between the most basinward fault (known as the outboard fault, which includes the severed fault tip), the overlapping fault (inboard fault), and any ramp-breaching linking faults. Along the Warner Valley fault in south-central Oregon, two relay ramps displaying different fault linkage geometries are lined with a series of pluvial shorelines that record a Pleistocene paleolake regression. The inner edges of these shorelines act as paleo-horizontal datums that have been deformed by fault activity, and are used to measure relative slip variations across the relay ramp bounding faults. By measuring the elevation changes using a 10m digital elevation model (DEM) of shoreline inner edges, I estimate the amount of fault activity on severed fault tips. In order to attribute shoreline deformation to fault activity I identify shoreline elevation anomalies, where deformation exceeds a ± 0.3% window from normalized elevation values; this encompasses my conservative estimates of natural variability in the shoreline geomorphology and the error associated with the data collection. For each ramp-breaching fault style activity is concentrated near the fault linkage site. Even after a ramp is fully breached the severed fault tip temporarily retains some connectivity to the main fault segment. Severed fault tips along a mid-ramp breach tend to be more active than the severed fault tip at a footwall breach. Persistent fault activity along the entire severed fault tip is dependent on the position of the linkage. These results indicate that on the time scale of 104 years after linkage, severed fault tips persist as active structures and accommodate meaningful amounts of strain. / 1 / Christopher Samuel Young

Mason, Texas and the surrounding areas have been previously studied and mapped at small scales, showing the large normal faults that cut through the area. Many secondary faults exist close to the large faults, and are not mapped in previous studies because of the small scale of the maps. The large number of faults, when the smaller secondary faults are considered, makes Mason a good place for studying the nature of normal faults in this region and making generalizations about their nature. This thesis examines one of these faults, the McMillan Fault, and the secondary faults in its hanging wall at a large scale, in order to assess the nature of normal faults in the Mason area. The McMillan Ranch in Mason, Texas, was mapped at a scale of 1:7,000 using both traditional and digital mapping methods, to determine the lengths and displacements of each fault, and attempt to determine a length/displacement ratio which can be applied to all normal faults in this area. A single length/displacement ratio was not determined, just as in previous studies. This study determined that the normal faults in the area are planar, high angle normal faults with varying displacement amounts. As a result, observations determined that deformation in the hanging wall of normal faults exceeded the deformation in the footwalls of the same faults. The main fault on the McMillan Ranch is the McMillan Fault, and its shape is determined based upon the orientation of the subsidiary normal faults in its hanging wall. A detailed study of the geology of the McMillan Ranch and the surrounding area, including a geologic history of the area, geologic map and cross section, and stratigraphic descriptions including bed-by-bed descriptions, stratigraphic column, and thin sections of each unit was carried out as a preliminary step to perform analyses of the faults on the ranch. The presence of the McMillan Fault was already known, and the pasture that was chosen for this study was best represented at a scale of 1:7,000. At such a large scale, it was necessary to recognize precisely where in the stratigraphic section the mapper was located, as some subsidiary faults were recognized by beds missing, rather than entire units. The structural data gathered from the field convey the varying natures of faults, even within the same area, and support the conclusion that length alone is not sufficient to predict displacement value on a fault.

Le domaine valaisan dessine la suture majeure qui marque la limite entre les zones internes et externes des Alpes occidentales et dont l'interprétation géodynamique était controversée. Cette suture est constituée d'une série de flysch (le flysch valaisan) et d'un complexe magmatique et sédimentaire (le complexe du Versoyen). Suivant les auteurs, les roches magmatiques d'affinité tholéïtique pourraient représenter: 1) une klippe d'origine piémontaise (suture d'hyper-collision), 2) une écaille ophiolitique située au front d'un prisme d'accrétion (suture océanique), 3) un complexe magmatique lié à un amincissement crustal (inversion structurale). Le but de ce travail était de trouver des arguments qui permettaient de résoudre cette controverse. Ainsi les résultats de ce travail montrent que : - Dans la région du col du Petit-Saint-Bernard (frontière franco-italienne), certaines tholéïtes sont recoupées par des filons leucocrates qui correspondent à des liquides différenciés, cogénétiques du magmatisme. Les datations UlPb sur les zircons contenus dans l'un de ces filons indiquent un âge Carbonifère supérieur- Permien inférieur pour le magmatisme du Versoyen. - Ce magmatisme présente des caractères géochimiques et isotopiques, intermédiaires entre ceux des N-MORB et des T-MORB, dans les régions du col du Petit-Saint-Bernard et de Visp (Suisse). Ces tholéïtes dériveraient de la fusion partielle d'un manteau appauvri (de type N-MORB), avec probablement la participation d'une source enrichie (de type OIB), ce qui est en accord avec une mise en place dans un domaine en cours d'océanisation. - Le complexe du Versoyen est affecté par un métamorphisme polyphasé éclogitique, puis schiste bleu et enfin schiste vert. La paragénèse éclogitique correspond à des conditions de Haute-Pression et Basse-Température (P > 13Kb, 425 < T < 475°C) qui traduisent un enfouissement à grande profondeur, lié à une subduction. Les datations Ar/Ar réalisées sur les phengites donnent des âges de refroidissement proches de 33 Ma et permettent d'établir le chemin P-T-t de ce complexe au cours de l'exhumation des éclogites. - Le complexe du Versoyen est affecté par une déformation syn-schiste vert qui correspond à un jeu normal vers le SE. La comparaison entre les données de terrain et les données sismiques ECORS suggère que les failles normales se prolongent en profondeur et s'applatissent vers 10-15 km. Cette déformation postérieure à 38 Ma explique en partie l'exhumation des éclogites. Ce jeu normal est contemporain de chevauchements dans la zone externe et pourrait accommoder un réamincissement crustal au cours de la collision alpine. Ces données montrent que l'individualisation du substratum du domaine valaisan est liée au cycle hercynien et que ses relations complexes avec le flysch sus-jacent sont liées à une inversion structurale anté-flysch, alors que son évolution tectono-métamorphique est controlée par une extension succèdant aux phases compressives.

After water vapour, CO₂ is the most abundant gas associated with magmatic hydrothermal systems. The detection of anomalous soil temperature gradients, and/or a significant flux of magmatic volatiles, is commonly the only surface signature of an underlying high temperature reservoir. For both heat (as water vapour) and gas to ascend to the surface, structural permeability must exist, as the unmodified bulk permeability of reservoir rock is too low to generate the focussed fluid flow typical of magmatic hydrothermal systems. This thesis reports the investigation into the surface heat and mass flow of the Ohaaki hydrothermal field using detailed surface measurements of CO₂ flux and heat flow. Detailed surface measurements form the basis of geostatistical models that quantify and depict the spatial variability of surface heat and mass flow, across the surface of both major thermal areas, as high resolution pixel plots. These maps, in conjunction with earlier heat and mass flow studies, enable: (i) estimates of the pre-production and current CO₂ emissions and heat flow for the Ohaaki Field; (ii) interpretation of the shallow permeability structures governing fluid flow, and; (iii) the spatial relationships between pressure-induced ground subsidence and permeability. Heat flow and CO₂ flux surveys indicate that at Ohaaki the soil zone is the dominant (≥ 70% and up to 99%) pathway of heat and mass release to the atmosphere from the underlying hydrothermal reservoir. Modelling indicates that although the total surface heat and mass flow at Ohaaki is small, it is highly focused (i.e., high volume per unit area) relative to other fields within the Taupo Volcanic Zone (TVZ). Normalised CO₂ emissions are comparable to other volcanic and hydrothermal fields both regionally and globally. Despite 20 years of production, there is little difference between pre-production and current CO₂ emission rates. However, the similarity of CO₂ emission rates masks a 40% increase in CO₂ emissions from new areas of intense steaming ground that have developed in response to production of the field for electrical energy production. This increase in thermal ground emissions is offset by emission losses associated with the drying up of all steam heated pools and alkali-Cl outflows from the Ohaaki West (OHW) thermal area, in response to production-induced pressure decline. The location of surface thermal areas is governed by the occurrence of buried or partially emergent lava domes, whereas the magnitude of CO₂ flux, mass flow, and heat flow occurring within each thermal area is determined by the proximity of each dome (thermal areas) to major upflow zones. Buried or partially emergent silicic lava domes act as cross-stratal pathways for fluid flow, connecting the underlying reservoir to the surface, and bypassing several hundred metres of the poorly permeable Huka Falls Formation (HFF) caprock. For each dome complex the permeable structures governing fluid flow are varied. At Ohaaki West, thermal activity is controlled by a deep-rooted concentric fracture zone, developed during eruption of the Ohaaki Rhyolite dome. Within the steam-heated Ohaaki East (OHE) thermal area, flow is controlled by a high permeability fault damage zone (Broadlands Fault) developed within the apex of the Broadlands Dacite dome. Structures controlling alkali-Cl fluid flow at OHW also iii appear to control the occurrence and shape of major subsidence bowls (e.g., the Main Ohaaki Subsidence Bowl), the propagation of pressure decline to surface, and the development and localization of pore fluid drainage. Across the remainder of the Ohaaki field low amplitude ground subsidence is controlled by the extent of aquifer and aquitard units that underlie the HFF, and proximity to the margins of the hot water reservoir. The correlation between the extent of low amplitude ground subsidence and the margins of the field reflects the coupled relationship between the hot water reservoir and reservoir pressure. Only where thick vapour-phase zones buffer the vertical propagation of deep-seated pressure decline to the surface (i.e., OHE thermal area), is ground subsidence not correlated with subvertical structural permeability developed within the HFF. This thesis makes contributions to regional and global research on geothermal and hydrothermal systems by: (i) quantifying the origin, mass, and upward transport of magmatic carbon from geothermal reservoirs; (ii) assessing the changes to the natural surface heat and mass flow of the Ohaaki Field following 20 years of production; (iii) establishing the utility of surface CO₂ flux and heat flow surveys to identify major upflow zones, estimate minimum mass flow, and determine the enthalpy of reservoirs; (iv) providing insight into the hydrothermal, structural and lithological controls over hydrothermal fluid flow; (v) demonstrating the influence of extinct silicic lava domes as important structural elements in the localisation of hydrothermal fluid flow; (vi) identifying the hydrostructural controls governing the spatial variability in the magnitude of pressure-induced ground subsidence, from which predictive models of subsidence risk may be defined, and; (vii) developing new technologies and characterising methods used for detailed assessment of surface heat and mass flow.

Microbial life on Mars is not visible from orbit or by rover cameras, but the fracture networks and scarp morphologies associated with fractures they could live in are measurable. We conducted a field analogue study of 92 normal fault scarps in the Sheepshead Mountains, Oregon to examine the correlation between scarp morphology and vegetation growth in the Steens Basalt. While vegetation is not expected on Mars, the fracture networks that sustain vegetation offer the same micro-environment that would support and protect endoliths. Structural variables were measured in the field and infrared spectra of fault scarps were measured using a handheld multispectral camera and vegetation indices were calculated from these images. Statistical analysis of the scarp morphologic parameters indicate that interconnectedness of fractures is key for elevated vegetation and is represented by a range of parameters. Results support a model for ideal slopes to investigate for preserved biological activity on Mars.

No description available.

Thesis (M.S.)--Miami University, Dept. of Geology, 2005. / Title from first page of PDF document. Document formatted into pages; contains [1], iv, 38 p. : ill. Includes bibliographical references (p. 35-38).

No description available.

The surface expression of upper crustal deformation varies widely based on geologic settings. Normal faults within an intra-arc basin, strike-slip faulting within a wide shear zone, and creeping fault behavior all manifest differently and require a variety of techniques for analysis. In this dissertation I studied three different actively deforming regions across a variety of geologic settings. First, I explored the drivers of extension within the La Pine graben in the Oregon Cascades. I mapped >20 new Quaternary faults and conducted paleoseismic trenching, where I found evidence for a mid-late Holocene earthquake on the Twin Lakes maar fault. I suggest that tectonics and not volcanism is responsible for the most recent deformation in the region based on fault geometries and earthquake timings, although more research is needed to tease out finer temporal and genetic relationships between tectonics and volcanism regionally. Second, I investigated the rupture pattern and earthquake history of the Calico fault system in the Eastern California Shear Zone. We mapped ~18 km of continuous rupture, with a mean offset of 2.3 m based on 39 field measurements. We also found evidence for two earthquakes, 0.5 - 1.7 ka and 5.5 - 6.6 ka through paleoseismic trenching. We develop a number of different multifault rupture scenarios using our rupture mapping and rupture scaling relationships to conduct Coulomb stress change modeling for the most recent earthquake on the Calico fault system. We find that the most recent event places regions adjacent to the fault in a stress shadow and may have both delayed the historic Landers and Hector Mine ruptures and prevented triggering of the Calico fault system during those events. Last, I studied the spatial distribution of the southern transition zone of the creeping section of the San Andreas fault at Parkfield, CA to determine if it shifted in response to the M6 2004 Parkfield earthquake. I used an Iterative Closest Point algorithm to find the displacement between two lidar datasets acquired 13 years apart. I compared creep rates measured before the 2004 earthquake to creep rates calculated from my lidar displacement results and found that there is not a discernible change in the overall pattern or distribution of creep as a response to the 2004 earthquake. Peaks within the lidar displacement results indicate complexity in the geometry of fault locking. / Doctor of Philosophy / Fault behavior varies widely across different regions, depending on the type of fault and local geology. In this dissertation I examine three regions with different mechanisms controlling deformation within them. First, I study the relationship between volcanic and tectonic induced faulting in the La Pine graben in the Oregon Cascades. While volcanoes and tectonics can both produce faults within a region, the surface expression of those faults changes depending on the underlying driver. I map > 20 new faults in the La Pine graben. I also conduct paleoseismic trenching on one of the newly identified faults, the Twin Lakes maar fault, and find that its most recent rupture occurred < 7.6 ka. I conclude that tectonism is the dominant driver of faulting within the La Pine graben based on the fault geometries and timing between identified regional earthquakes and volcanism. Second, I explore recent rupture on the Calico fault system in the Eastern California Shear Zone, which is a wide region across eastern California where deformation is distributed among many faults. Faulting in this region is complex, with some earthquakes occurring on multiple connected faults. I conducted a paleoseismic survey to determine the timing of the most recent earthquake(s) on the Calico fault system. This trenching effort found evidence for 1-2 earthquakes, the most recent occurring 0.5 – 1.7 ka. I use the rupture mapping and earthquake timing to develop a number of various rupture scenarios. I use these scenarios as inputs for computer modeling to explore the regional stress changes from these events and find that they reduce the overall stress in the area, elongating the amount of time between regional earthquakes. Last, I examine how creeping fault behavior on the San Andreas fault near Parkfield, CA changes as a response to an earthquake. Creeping behavior is where the two sides of a fault are continuously moving past one another. I examine the spatial distribution of where the San Andreas fault transitions from creeping to locked behavior by differencing two high-resolution lidar topographic datasets taken after the M6 2004 Parkfield earthquake. I compare my displacement results to pre-2004 datasets and conclude that the transition zone did not appreciably change as a result of the earthquake.

A detailed structural study of Rock Canyon (near Provo, Utah) provides insight into Wasatch Range tectonics and fold-thrust belt kinematics. Excellent exposures along the E-W trending canyon allow the use of digital photography in conjunction with traditional field methods for a thorough analysis of Rock Canyon's structural features. Detailed photomontages and geometric and kinematic analyses of some structural features help to pinpoint deformation mechanisms active during the canyon's tectonic history. Large-scale images and these structural data are synthesized in a balanced cross section, which is used to reconstruct the structural evolution of this portion of the range. Projection of surficial features into the subsurface produces geometrical relationships that correlate well with a fault-bend fold model involving one or more subsurface imbrications. Kinematic data (e.g. slickenlines, fractures, fold axes) indicate that the maximum stress direction during formation of the fault-bend fold trended at approximately 120°. Following initial thrusting, uplift and development of a thrust splay produced by duplexing may have caused a shift in local stresses in the forelimb of the Rock Canyon anticline leading to late-stage normal faulting during Sevier compression. These normal faults may have activated deformed zones previously caused by Sevier folding, and reactivated early-stage decollements found in the folded weak shale units and shaly limestones. Movement on most of these normal faults roughly parallels stress directions found during initial thrusting indicating that these extensional features may be coeval with thrusting. Other zones of extension and brittle failure produced by lower ramp geometry appear to have been activated during Tertiary Basin and Range extension along the Wasatch Fault Zone. Slickenline data on these later normal faults suggest a transport direction of nearly E-W distinguishing it from earlier events.