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No description available.

<p> The Davis-Schrimpf Seep Field is a cluster of about 50 transtension-related geothermal seeps in the Imperial Valley, southeastern California. Five temperature time-series were collected from four features and compared to one another, against prior time-series, and to local seismicity. Loggers placed in separate vents within one seep returned moderate anti-correlation. Vents may selectively clog and unclog. Clogging frequencies explaining the observed level of negative correlation were given. Loggers placed in the same vent produced 87-92% positive correlation. It is therefore likely that the vast majority of temperature data measured with loggers possesses meaningful accuracy. Loggers placed in separate seeps exhibited correlation close to or greater than the statistically significant 60% threshold. I propose two lineaments provide a hydraulic connection between these seeps. Two M_w>3.0 earthquake swarms, including one M_w>4.0 event, within 24 kilometers showed possible linkage with >5 degree Celsius temperature perturbations. Seepage warmed 14.5-36.8 degrees Celsius over 5-7 years.</p>

Tertiary history of the Pacific Northwest is closely tied to that of the Columbia River Flood Basalt (CRB) events. The region is, geologically, one of the least well understood parts of the continental United States. Throughout the Neogene, the Columbia Basin and surrounding terrains appear to have been shaped not by horizontal tectonic forces, but by deep dynamic forcing, driving apparent “vertical tectonics.” This class of phenomena appears to be at odds with the traditional tenets of plate tectonics, and yet may prove to be ubiquitous geologic processes worldwide. Many of the processes described here are unique to volcanically-active regions, such as those affected by CRB eruptions and deposition. In the following chapters I will discuss several physical mechanisms by which lithosphere can deform in the absence of horizontal tectonic stress. These include analyses of the mechanisms associated with metamorphic densification, rheologic transformation owing to magmatic intrusions, and the dynamics of lithospheric delamination. All code and documentation to reproduce the results presented here can be found in the supplemental files included with this dissertation. Appendices A and B document the purpose, usage, and functionality of each supplementary file. This dissertation includes previously published and unpublished coauthored material.

The collision of the Indian subcontinent with Asia beginning 40 million years ago produced the Himalayan orogenic belt, the largest continental collision belt active today. The foreland fold-and-thrust belt in northern Pakistan consists of the Salt Range-Potwar Plateau area. In this region the distance from the Main Boundary Thrust(MBT) to the front of the fold-and-thrust belt is very wide (100-150 km) because a thick evaporite sequence forms the zone of décollement. Recent studies have combined seismic reflection profiles, petroleum exploration wells, Bouguer gravity anomalies, and surface geology to construct cross sections in the eastern, central, and western Salt Range-Potwar Plateau areas. In this study the sections are compared with a previous model that considers the mechanics of a fold-and-thrust belt to be analogous to that of a wedge of snow or soil pushed in front of a bulldozer (Davis et al., 1983; Dahlen et al., 1984; Dahlen, 1984), and a later model (Davis and Engelder, 1985) which suggests that fold-and-thrust belts underlain by salt will have: a) narrow (< 1°) cross-sectional tapers, b) larger widths than areas not underlain by salt, c) symmetrical structures, and d) changes in deformational style at the edge of the salt basin. The section across the eastern Potwar Plateau most closely resembles this latter model, having: a) a taper of 0.8° ± 0.1°, b) a width of 100-150 km, c) thrust faults that verge both to the north and south, and d) structures rotated 30° counterclockwise with respect to the Salt Range. From the observed taper and pore fluid pressures of the eastern Potwar Plateau, estimates of the values for the yield strength of the evaporites (τ₀) and the coefficent of internal friction (μ) are calculated as τ₀ = 1.33-1.50 MPa and μ = 0.95-1.04, which are then applied to the other cross sections. In the central and western sections a basement uplift, the Sargodha High, interferes with the front of the fold-and-thrust belt. This feature causes the ramping of the Salt Range Thrust and produces a relatively steep basement slope (2°-4°) beneath the Potwar Plateau. This dip, together with the weak evaporite layer, allows the thrust wedge of the southern Potwar Plateau to be pushed over the décollement without undergoing internal deformation. In detail, the Salt Range ramping is caused by a large normal fault in the basement in the central section and the basement upwarp of the Sargodha High in the western section. The northern Potwar Plateau is strongly folded and faulted, yet the topographic slope remains flat. Although the deformation suggests that salt is not present there, the observed taper in the northern Potwar Plateau is best fitted by the model with salt at the décollement. Combining this with published paleomagnetic and geologic constraints, a model for the evolution of the northern Potwar Plateau suggests that the area deformed as a steeply tapered (3.5°-5.5°) thrust wedge until approximately 2 million years ago, when the décollement encountered the Salt Range formation. Between 2 m.y.a. and the present, the northern Potwar Plateau has been pushed along the salt décollement without deformation, and erosion has reduced its original steep topographic slope to a nearly level surface. The success of the mechanical model in predicting the observed features in the Salt Range-Potwar Plateau suggests that salt may lie beneath other fold-and-thrust belts in Pakistan. Two areas, the Sulaiman Lobe and the Karachi Arc, are possible candidates. Although published subsurface information is lacking in these areas, surface observations show that they both: a) extend far across the foreland, b) exhibit low topographic slopes, c) display symmetrical structures, and d) show a change in structural orientation along what is believed to be the edge of the salt basin. / Graduation date: 1987

Modern, powerful techniques for the residual analysis of spatial-temporal point process models are reviewed and their power under various null and alternative hypotheses is compared. Residual methods can be divided into two schemes: transformation-based and pixel-based methods. Rescaling, thinning and superposition are useful transformation-based methods for the residual analysis of spatial-temporal point processes. These techniques involve transforming the original point process into a new process that should be a homogeneous Poisson process if and only if the fitted model is correct, so that one may inspect the residual process for homogeneity using standard tests for homogeneity as a means of assessing the goodness-of-fit of the model. Unfortunately, tests of homogeneity performed on residuals based on these three residual methods tend to have low power when the modeled conditional intensity of the original process is volatile. For such purposes, we propose the method of super-thinning, which combines thinned residuals and superposition. This technique involves the use of a tuning parameter, k, which controls how much thinning and superposition are performed to homogenize the process. The method is applied to the assessment of a parametric space-time point process model for the origin times and epicentral locations of recent major California earthquakes. / These residual methods are then applied to California earthquake forecast models used in the Collaboratory for the Study of Earthquake Predictability (CSEP). Assessments of these earthquake forecasting models have previously been performed using simple, low-power means such as the L-test and N-test. We instead propose using the transformation residual methods for model assessment, and the pixel-based methods, such as Pearson and deviance residuals, to compare competing models. The different residual analysis techniques are demonstrated using the CSEP models and are used to highlight certain deficiencies in the models. / Both pixel-based and transformation methods are evaluated through a simulation study by applying each method to a group of Hawkes processes that contain different degrees of clustering and inhibition. Pixel-based methods, such as raw, Pearson, inverse, deviance, and tessellation residuals appear to be generally weaker than transformed residuals at detecting insufficient or excessive local clustering in the model. The transformation method of super-thinning is shown to have relatively high power when the value of the tuning parameter, k, is carefully chosen. / Finally, we introduce the R package stppResid, which implements both transformation and pixel-based residual analysis for space-time point process models. We illustrate the use of each of these residual tools by applying them to a well known space-time point process model fitted to a red banana data set.

Arc-continent collisions are a fundamental plate tectonic process that control continental growth, orogen development and the distribution of natural hazards and natural resources. This process actively occurs in Taiwan where the Luzon Volcanic Arc collides obliquely with the passive margin of the Eurasian Plate. An important characteristic of the arc-continent collision in Taiwan is that oblique convergence has produced an orogen that decreases in age from north to south. Investigation of the temporal evolution of the Taiwan orogen is therefore made possible through studies at different latitudes on the island. The first long-period magnetotelluric (MT) measurements in Taiwan were recorded at 82 locations on three profiles across south, central and north Taiwan during 2006-2007. These MT data were collected as a component of the TAIGER (Taiwan Integrated Geodynamics Research) project and are analyzed and interpreted in this thesis. The TAIGER project was initiated to: 1) collect multi-technique high resolution geophysical data required to unambiguously distinguish between end-member tectonic models proposed for central Taiwan, and 2) to investigate the orogen evolution by comparison of data collected at latitudes ranging from south to north Taiwan. In this thesis, the central Taiwan TAIGER MT data are shown to be inconsistent with orogen-scale thin-skinned tectonic models and instead support predictions of lithospheric-scale deformation (i.e. thick-skinned tectonics) beneath the Central Ranges. Similarity between resistivity models of central and southern Taiwan indicate that thick-skinned tectonics is occurring in both locations, and is therefore a persistent mode of deformation that operates as the orogen develops. The resistivity model for northern Taiwan is shown to be consistent with dewatering of the subducting Philippine slab, and with deformation described by the subducting indenter tectonic model. A global context for the Taiwan results is provided by comparison to the South Island of New Zealand that shares many similarities with the tectonic setting in Taiwan. MT resistivity models support lithospheric deformation beneath the Southern Alps, and the occurrence of fluid-based conductors in the Marlborough region caused by dewatering of the Pacific slab. / Geophysics

Detailed geologic mapping of portions of the Banoak, Reepsville, Lincolnton West, and Cherryville 7.5-minute quadrangles has confirmed the easternmost exposure of the Brindle Creek fault, which frames the Newton window. The Brindle Creek fault is a terrane boundary that separates the overlying Siluro-Devonian assemblage of metasedimentary rocks and Devonian-Mississippian anatectic plutons of the Cat Square terrane from the Neoproterozoic(?)-Ordovician metasedimentary and igneous rocks of the Tugaloo terrane. Structures related to six deformational events have been identified in this portion of the Inner Piedmont. The Brindle Creek fault has been folded multiple times, resulting in a sinuous outcrop pattern and the formation of the Newton window and smaller Howards Creek window. Portions of three map-scale sheath folds have been identified by map patterns and orientation of dominant mineral lineations, fold axes, and shear-sense indicators. The discontinuity of map-scale bodies of metagraywacke, mafic complexes, and amphibolite is attributed to extension during sheath fold formation. Dominant foliation, mineral lineation, and fold-axis orientations suggest north-northwest directed flow occurred in this portion of the Inner Piedmont. Zircon geochronology data indicate crystallization of the Vale charnockite at 366.4 ± 3.1 Ma and the enclosing Walker Top Granite at 356.5 ± 5.3 Ma. Zircon saturation thermometry estimates minimum magmatic temperatures for the granitoids at 800-840⁰ C. Whole-rock geochemical and isotopic data indicate the Vale charnockite and Walker Top Granite are genetically related and were derived from deep crustal melting of largely Proterozoic-affinity metasediments in an arc environment. Both granitoids crystallized from the same parent magma; the Vale charnockite is an autolith, or early crystallization of the melt, incorporated into the later crystallizing Walker Top Granite. Geochemical analyses of Cat Square terrane mafic complexes west of the Newton window suggest these bodies represent vestiges of oceanic crust formed in a back-arc basin setting or from both MORB and volcanic-arc sources as characterized by mixed N-MORB and calc-alkaline volcanic-arc signatures. This back-arc basin likely formed from east-dipping subduction during the development of Ordovician volcanic arcs outboard of Laurentia.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

The evolution of the Caribbean --- South America plate boundary has been a matter of vigorous debate for decades and many questions remain unresolved. In this work, and in the framework of the BOLIVAR project, we shed light on some aspects of the present state and the tectonic history of the margin by using different types of geophysical data sets and techniques. An analysis of controlled-source traveltime data collected along a boundary-normal profile at &sim;65&deg;W was used to build a 2D P-wave velocity model. The model shows that the Caribbean Large Igenous Province is present offshore eastern Venezuela and confirms the uniformity of the velocity structure along the Leeward Antilles volcanic belt. In contrast with neighboring profiles, at this longitude we see no change in velocity structure or crustal thickness across the San Sebastian - El Pilar fault system. A 2D gravity modeling methodology that uses seismically derived initial density models was developed as part of this research. The application of this new method to four of the BOLIVAR boundary-normal profiles suggests that the uppermost mantle is denser under the South American continental crust and the island arc terranes than under the Caribbean oceanic crust. Crustal rocks of the island arc and extended island arc terranes of the Leeward Antilles have a relatively low density, given their P-wave velocity. This may be caused by low iron content, relative to average magmatic arc rocks. Finally, an analysis of teleseismic traveltimes with frequency-dependent kernels produced a 3D P-wave velocity perturbation model. The model shows the structure of the mantle lithosphere under the study area and clearly images the subduction of the Atlantic slab and associated partial removal of the lower lithosphere under northern South America. We also image the subduction of a section of the Caribbean plate under South America with an east-southeast direction. Both the Atlantic and Caribbean subducting slabs penetrate the mantle transition zone, affecting the topography of the 410-km and 660-km discontinuities.