First, an updated Pacific paleomagnetic skewness pole for chron 32 (72 Ma) is presented. The updated paleomagnetic pole corrects for the spreading-rate dependence of anomalous skewness, a correction which hasn't been applied to Pacific skewness poles before. The presence of anomalous skewness is one of the main factors limiting the accuracy of paleomagnetic poles determined from the skewness data. Thus, successfully correcting for the anomalous skewness, as was done in this study, significantly improves the reliability of the skewness poles. The earlier assertions that the Hawaiian hotspot has shifted southward relative to the spin axis by 13° since ≈72 Ma are also confirmed. Second, updated reconstructions of the Pacific plate relative to the hotspots for the past 68 million years are presented, with the uncertainties in the reconstructions. Plate-circuit reconstructions are used to predict the tracks of some major Indo-Atlantic hotspots (Tristan da Cunha, Reunion and Iceland) from the Pacific-hotspot plate motion and the rates of relative motion between the Pacific and Indo-Atlantic hotspots are estimated. Within the uncertainties, motion between the hotspots is found insignificant for the past 48 million years. For earlier times, a systematic error in the plate circuit used to make the predictions is inferred and which may be due to unmodeled motion between East and West Antarctica. If the observed discrepancy can be shown to correspond to an error in the plate circuit, the southward motion of the Hawaiian hotspot of 13° since ≈72 Ma can likely be attributed to true polar wander. Building on the above-mentioned work, finally, for the first time, a globally self-consistent model of plate motions relative to the global hotspots for the past 48 million years is presented, and the implications of this model to the question of relative hotspot motion discussed. The provided globally self-consistent set of reconstructions can be used as a fixed frame of reference for absolute plate motions, and true polar wander, for the past 48 million years.

The sedimentary wedge of the northern Gulf of Mexico is extensively deformed and faulted by salt tectonics. Industry 2-D multichannel seismic data covering a large area (33,800 km2) of the lower Texas continental slope [96 degrees 40'- 93 degrees 40'W; 27 degrees 10N - 26 degrees N] were examined to evaluate the interplay of salt, faults and gas. Seismic interpretation revealed the study area has two different styles of faulting and two different types of salt bodies that vary east to west. The eastern region of the study area has a thin sedimentary section and a massive, nearly continuous salt sheet characterized by minibasins and local salt highs. Faulting in this area appears to be the result of salt tectonism. The western region of the study area has a thick sedimentary wedge, and a few isolated salt diapirs. Long, linear faults are parallel to slope and imply some degree of gravitation sliding. The difference in faulting styles and salt bodies can be attributed to different depositional environments, different styles and amounts of sediment loading and different amounts of salt initially deposited. While there is a widespread occurrence of gas throughout the study area, little evidence of continuous bottom simulating reflectors (BSRs), a widely accepted geophysical indicator of gas hydrate, has been found. The gas hydrate stability zone (GHSZ) was modeled to provide information on the thickness and variability of the stability zone, and provide a baseline in a search for BSRs. The dataset was analyzed for multiple seismic expressions of BSRs, however only a few small and isolated examples were found. Potential fluid escape structures were seen in the seismic data. Despite the great number of potential features found in the seismic data only seven active seeps were found in a seep study by I. R. MacDonald. Seeps were seen in far less abundance than the number of seeps found offshore Louisiana. This may imply a lack of source offshore Texas.

Thesis (M. Sc.) -- University of Canterbury, 2009. / Also available via the World Wide Web.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Arc-continent collision is associated with vigorous mountain building and terrane accretion on relatively short (<10 Ma) geologic timescales. It is believed to be an important mechanism for the growth of continents. Taiwan represents one of the few active examples of this process. As such, is the perfect natural laboratory to investigate the nature of the continent ocean boundary and the uncertain behavior of the accretionary prism and extended, transitional rifted margin crust during the collision process. Taiwan also provides a unique opportunity to investigate structures in the backarc, yielding key insights into the still controversial tectonic conditions that were responsible for the unique subduction-collision system observed today. The obliquity of the collision between the North Luzon Arc and the Chinese rifted margin allows for examination of different temporal stages of collision at different locations. Recently acquired seismic reflection and wide-angle seismic refraction data, offshore Taiwan, document the crustal structure of the incipient mountain belt and of the Philippine Sea Plate in the backarc domain to the east. Geophysical profiles offshore southern Taiwan show evidence for a transition from the subduction of ocean crust to highly extended, transitional continental crust of the northern South China Sea distal margin. During oceanic subduction, accretion and underplating of thick sedimentary cover sequences create a large 13-15 km thick accretionary prism. Prior to the encroachment of the continental shelf, there is evidence for further underplating of transitional distal margin crust to the base of the prism. These findings support a multi-phase collisional model in which early growth of the mountain belt is driven by structural underplating of the previously sedimentary-only accretionary prism with blocks of transitional crust from the distal rifted margin. Geophysical profiles offshore eastern Taiwan show evidence for asymmetric crustal thickening, from 12-18 km, along the entire length of the Gagua Ridge suggesting the West Philippine Basin oceanic crust is underthust beneath that of the Huatung Basin. In this interpretation, the Gagua Ridge was the result of a failed subduction initiation event during the early Miocene that may have existed simultaneously and, for a short time, competed with the Manila subduction zone in accommodating convergence between the Eurasia and Philippine Sea plates. / text

Geodetic observations provide kinematic constraints on the behavior of tectonically active fault systems. Estimates of earthquake cycle activity derived from these constraints may depend on modeling assumptions and/or regularization of a geodetic inverse problem, which is often poorly conditioned. Common model assumptions may affect kinematic solutions and conclusions about physical properties of faults and fault zones. For example, within a geometrically complex fault system, parameterization of nearby faults may affect slip estimates on an individual fault. In addition, fault slip models are often regularized by assuming that slip varies smoothly in space, which may artificially smear slip estimates beyond physical boundaries. As an alternative to smooth regularization, the applied mathematics field of compressed sensing provides a suite of methods for recovering sparse solutions. Applied to GPS observations of the 2011 Tohoku earthquake, compressed sensing algorithms enable imaging of spatially localized slip during and following the earthquake, and identification of a sharp boundary between coseismic and postseismic slip. Similar algorithms recover quantized solutions and may be applied to models of plate boundary deformation. Beginning with a dense array of tectonic micro-plates bounded by mapped faults in North America, these methods can be used to detect coherent motions of groups of micro-plates behaving as larger active blocks, effectively quantifying the complexity of North America plate boundary deformation. By improving our ability to identify and compare kinematic constraints on earthquake cycle processes, we are able to characterize the spectrum of earthquake cycle behaviors and gain a deeper understanding of earthquake phenomenology and physics. / Earth and Planetary Sciences

Not available / text

Convergent continental margins are regions of intense deformation caused by the interaction of oceanic plates with continents. The spatial extent of deformation is broadly commensurate with the specific time scale of the causative phenomenon. For example, subduction-related short-term deformation is limited to <200 km from the margin, whereas long-term plate convergence cause deformation over ∼1000 km landward. Deformation is thus manifested in multiple ways, with attributes depending on the scale of measurement. In this thesis we investigate the use of two geophysical approaches in the study of deformation: 1) The analysis of potential-field anomalies to derive estimates of the elastic thickness (Te) of the lithosphere, and 2) The structural study of past and present subduction systems using seismic observations and modelling. Both approaches involve the development of appropriate methodologies for data analysis and modelling, and their application to the western Canadian landmass. Our findings are summarized as follows: 1) We develop a wavelet-based technique to map variations in Te and its anisotropy; 2) We show how a step-wise transition in Te and its anisotropy from the Cordillera to the Craton is a major factor influencing lithospheric deformation; 3) We implement a waveform modelling tool that includes the effects of structural heterogeneity and anisotropy for teleseismic applications, and use it to model the signature of a fossil subduction zone in a Paleoproterozoic terrane; 4) We use teleseismic recordings to map slab edge morphology in northern Cascadia and show how slab window tectonism and slab stretching led to the creation of the oceanic Explorer plate; 5) We use seismic signals from the subducting oceanic crust to calculate elevated Poisson’s ratio and infer high pore-fluid pressures and a low-permeability plate boundary within the forearc region of northern Cascadia.

<p> The history of late Miocene (Proto-Gulf) deformation on the Sonoran margin of the Gulf of California is key to understanding how Baja California was captured by the Pacific plate and how strain was partitioned during the Proto-Gulf period (12.5-6 Ma). The Sierra el Aguaje and Sierra Tinajas del Carmen are located in southwestern coastal Sonora, Mexico, and represent the eastern rifted margin of the central Gulf of California. The ranges are composed of volcanic units and their corresponding volcaniclastic units which are the result of persistent magmatic activity between 20 and 8.8 Ma, including three packages of basalt and andesite that make excellent paleomagnetic recorders. Based on cross cutting relations and geochronologic data for pre-, syn-, and post-tectonic volcanic units, most of the faulting and tilting in the Sierra El Aguaje is bracketed between 11.9 and 9.0 Ma, thus falling entirely within Proto-Gulf time. </p><p> A paleomagnetic investigation into possible vertical axis rotations in the Sierra el Aguaje has uncovered evidence of clockwise rotations between ~13&ordm; and ~105&ordm; with possible translations. These results are consistent with existing field relations, which suggest the presence of large (>45&deg;) vertical axis rotations in this region. This evidence includes: a) abrupt changes in the strike of tilted strata in different parts of the range, including large domains characterized by E-W strikes b) ubiquitous NE-SW striking faults with left lateral-normal oblique slip, that terminate against major NW-trending right lateral faults, and c) obliquity between the general strike of tilted strata and the strike of faults. These rotations occurred after 12 Ma and largely prior to 9 Ma, thus falling into the Proto-Gulf period. Such large-scale rotations lend credence to the theory that the area inboard of Baja California was experiencing transtension during the Proto-Gulf period, rather than the pure extension that would be the result of strain partitioning between Sonora and the Tosco-Abreojos fault offshore Baja California.</p>

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