Thesis (M.Sc.)--University of Adelaide, 1959.

Thesis (Ph.D.)--The Ohio State University, 2008. / (UMI)AAI3292725. Source: Dissertation Abstracts International, Volume: 68-12, Section: B, page: 7892. Adviser: Terry J. Wilson.

<p> An interdisciplinary approach at the interface between geodesy and geophysics has recently resolved several Earth science problems at regional and global scales. I use the term &ldquo;geophysical geodesy&rdquo; to distinguish the technical and theoretical aspect of geodesy from geophysical applications of geodetic techniques. Using a wide range of Earth observation data, I study the spatio-temporal characteristics of Earth surface deformation in the United States associated with several geophysical processes, including natural and anthropogenic subsidence and uplift, regional relative sea-level rise, and continental hydrological loading. The theoretical portion of this dissertation applies loading theory and develops a new hybrid method to improve the estimate of hydrologically-induced vertical deformation at time scales from sub-annual to multi-annual. The application part of this dissertation benefits from GPS and other geodetic and geologic data sets to study and model Earth&rsquo;s surface uplift due to CO2 injection at an oil reservoir in coastal Texas, and coastal subsidence and nuisance flooding along the Mississippi River Delta and eastern seaboard of the United States.</p><p>

<p> An important pursuit in volcanology is more accurate predictions of activity. One promising avenue for that pursuit is resonant seismic signals, and the data inherently contained in their resonance. As there is a strong correlation between such signals and the presence of gas, modelling the behavior of gas bubbles within a magmatic system is a critical step in this journey, as well as toward the overall understanding of the volcanic system. </p><p> I modelled clusters of bubbles using Boundary Element Method combined with Fast Multiple Method. The bubbles are three-dimensional polygonal meshes with triangular faces. The models are clusters of nearly 1000 bubbles arranged in rectangular prisms of dimensions 18x24x660, run with the long side at various angles, from 0&deg; to 90&deg;, to simulate bubbles nucleated from fresh magma injected into more mature magma. They were allowed to run until the meshes deformed too much, causing errors that render the simulations unviable from that point onward, which is long enough to see different behaviors emerge. </p><p> The models presented here show bubbles that behave in accordance with expectations based off of the properties of the Rayleigh-Taylor instability, which causes upwellings to develop in initially level clusters of buoyant materials, and show that above a critical angle of about 30&deg;, the instability disappears. In addition, this behavior also helps explain processes behind Strombolian activity, with clusters above the critical angle developing into a vertical cluster of evenly-spaced plumes, rather than clusters below the critical angle, which develop into plumes at the same height which would reach the surface at roughly the same time.</p><p>

<p> This project numerically modeled a simplified version of a fault system complete with a shear zone, similar to that of the fault zones in the Sierra Nevada, purely in Python to compare to that of one using ABAQUS. Modeling fluid flow in this system can help explain or predict where water is coming to the surface in places like the Sierra Nevada. The model took into account fluid flow based on Darcy&rsquo;s law, which explains how fluid flows through a porous media, and applied it to the background diffusivities and pressures that it was given. This gave fluid velocities off initial pressure gradients and perturbations. After testing several initial pressure fields in the model against the previous models, it was found that, with Test 3, it was possible to match the &ldquo;black box&rdquo; of ABAQUS using the freeware of Python. This result opens up opportunities to explore further this system by refining the model and adding new parameters that were just not possible to do with ABAQUS.</p><p>

This dissertation consists of several distinct studies that use numerical modeling to better constrain deformation due to faulting over disparate timescales. Field mapping reveals a segment of the Lake Mead fault system, the Pinto Ridge fault, and a cluster of west-dipping normal faults located near Pinto Ridge. I suggest that this strike-slip segment was kinematically related to the Bitter Spring Valley fault, created the normal fault cluster at Pinto Ridge, and utilized these normal faults as linking structures between fault segments. Modeling results demonstrate that the location and orientations of the normal faults are consistent with having formed in the perturbed stress field around the slipping Pinto Ridge fault. Calculations of mechanical efficiency suggest that a preferred dip of normal faults in the region may reflect a crustal anisotropy at depth, such as a detachment. I present a methodology for simulating interseismic deformation in complex regions. I derive an analytical model of interseismic deformation that is equivalent to the conventional model. Based on this model, I formulate a two-step numerical simulation of geologic and interseismic deformation. I apply this technique to the Los Angeles region and find that model results match well both geologic slip rate estimates and geodetic velocities. Model results suggest that the Puente Hills thrusts are currently slipping at rates that are compatible with geologic estimates and that localized contraction in the San Gabriel basin is dominantly due to deep slip on the Sierra Madre fault. To assess the control of fault geometry and mechanical interactions on fault slip in a natural system, I create models of the Ventura region, California, using both planar and non-planar faults. I find that incorporating geologically-constrained fault surfaces into numerical models results in a better match to available geologic slip rate data than models utilizing planar faults. Because slip rates at most locations along the surface traces of Ventura faults are not likely to represent average values for the entire fault surface, I propose that well-constrained models can be used to predict slip rates at specific locations and determine whether existing slip rate estimates are representative of average fault slip rates.

This thesis contains several distinct studies aimed at better understanding fracturing in compressional fault-cored folds. At outcrops of growth strata in the Oliana anticline in the Spanish Pyrenees, the relationship of two joint sets may reflect changing mechanical properties (i.e. via diagenesis) during the folding process. Using a Schmidt hammer, I assess the rigidity contrast between the individual units and suggest that late-stage, throughgoing joints formed in strata with conditions similar to those of the present day and that early, bed-contained joints formed when the rigidity contrast between beds was significantly greater than the present day contrast. Modeling algorithms that are used for fracture prediction assume plane strain to construct, model and restore fault-cored folds. Using mechanical models that allow heterogeneous transport in three dimensions, I explore the distribution and magnitude of out-of-plane transport in plunging fault-cored anticlines and provide guidelines of where plane strain should and should not be applied. I show that out-of-plane transport is significant in the simplest non-cylindrical folds, and suggest that complex non-cylindrical structures should not be modeled using plane strain. I mapped five bed-orthogonal fracture sets associated with folding and faulting events at Sant Corneli anticline, a non-cylindrical, fault related anticline in the Spanish Pyrenees. Fold axis perpendicular, calcite healed joint sets associated with similarly oriented normal faulting both pre-date, and are cross cut by calcite healed, N-NW striking joints. Later bed strike oblique joint sets are distinguished by the presence of iron oxide mineralization that probably occurred during Paleocene-Oligocene time. This study directly links fold-related fracturing to fold evolution because fracture sets can be dated relative to the structural evolution of the anticline. I use three-dimensional restorations of Sant Corneli anticline in the Spanish Pyrenees to test the fracture prediction capability of a fully three-dimensional finite element geomechanical restoration algorithm. Reconstruction of the three-dimensional architecture of the syn-tectonic strata provides a template for incrementally unfolding the anticline. Strains predicted by the restorations are compared to the fracture sets that formed over the corresponding time intervals, which are consistent with the observed fracture patterns at Sant Corneli anticline.

<p> Strain evolution and stress evolution following the 4 April 2010 M7.2 El Mayor-Cucapah earthquake are modeled using an adaptation of the strain transient detection tool developed by <i>Holt and Shcherbenko</i> 2013. The evolution of stress is calculated from postseismic strains, which are modeled from continuous GPS horizontal displacements. Strain fields are modeled in 2 ways; the total strain field based on total observed cGPS displacements, and the residual strain field, which subtracts a reference field from the total model. The residual shows anomalous strains resulting from the postseismic relaxation of the 2010 event. Anomalous and total strains are modeled in 0.1 year epochs for 2.4 years following the event. Both total and anomalous strains are converted into stress changes over time, assuming elastic incompressible behavior. Following the El Mayor event, the GPS constrained strain evolution shows the following: (1) The Southern San Andreas experiences a reduced rate of right-lateral strike slip strain accumulation between 3 July 2010 and 7 August 2012 (Figure 16a-d). (2) The San Jacinto Fault has normal rate of right-lateral strike-slip strain accumulation during this time. (3) Before the Brawley swarm of 26 August 2012, the state of strain evolves to enable unclamping of a left-lateral fault zone in the Brawley Seismic Zone (Figure 16a-d). (4) Large shear strains accumulate on the Laguna Salada Fault (northernmost segment)/southern Elsinore FZ (Figure 16a-d). We converted the strain changes into Coulomb stress changes on existing faults (both right-lateral and left-lateral). Several regions show increased Coulomb stress changes throughout the postseismic process. Furthermore, the Coulomb stress changes on the faults in the region progressively increase toward failure up to the time of the Brawley swarm.</p>

<p> The processes that generated the distinctive landscape of the Iowa Erosion Surface (IES) of northeastern Iowa have been debated for over a century. A number of researchers have concluded that the IES experienced a periglacial environment and was underlain by continuous permafrost during the last glacial maximum. Ubiquitous throughout the IES is a stone zone that lies 60-100cm below the surface. Several explanations for the genesis of the stone zone have been proposed, including a lag concentrate, biomantle processes, and cryogenesis. We utilized a combination of coring and trenching, ground penetrating radar and resistivity to investigate the 3D distribution of the stone zone, overlying "pedisediment" and the underlying contact with dense till across a 100m2 area on a typical IES hillslope in east-central Iowa . Our preliminary results indicate that the stone zone occurs in the basal few decimeters of pedisediment that rests uncomformably and abruptly on eroded, dense till. Ice wedge casts extend from the stone zone into the underlying till. The depth of the stone zone below the modern surface increases downslope and the stone zone dissipates and eventually is replaced by relatively thick loamy sand beneath the footslope. These relationships argue against the stone zone being of biogenic origin. The occurrence of ice wedge casts associated with the stone zone and systematic changes in the thickness and texture of the pedisediment suggest to us that stone zone on the IES was formed by a combination of cryogenic and active zone erosive processes during the full glacial period.</p>

<p>Mount Erebus, Antarctica, is a volcano with frequent lava-lake eruptions known as strombolian eruptions. The larger of these eruptions create strong seismic waves and have a characteristic seismic signature that can be analyzed through three-component cross-correlation to distinguish smaller strombolian eruptions from the background noise of the volcano. The addition of an infrared camera on the rim of Mount Erebus allows for the confirmation of strombolian eruptions as opposed to unrelated seismic activity. This research finds that eruption events can also be detected categorizing the images using machine learning. Machine learning in seismology is now a commonly used technique, yet to date, no research using machine learning has ever been used in volcanology. Image categorization along with cross-correlation can improve automatic detection of strombolian eruptions.