Browsing by Subject "Seismic"
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Item Analysis of GPU-based convolution for acoustic wave propagation modeling with finite differences: Fortran to CUDA-C step-by-step(2014-05) Sadahiro, Makoto; Stoffa, Paul L., 1948-; Tatham, R. H. (Robert H.), 1943-By projecting observed microseismic data backward in time to when fracturing occurred, it is possible to locate the fracture events in space, assuming a correct velocity model. In order to achieve this task in near real-time, a robust computational system to handle backward propagation, or Reverse Time Migration (RTM), is required. We can then test many different velocity models for each run of the RTM. We investigate the use of a Graphics Processing Unit (GPU) based system using Compute Unified Device Architecture for C (CUDA-C) as the programming language. Our preliminary results show a large improvement in run-time over conventional programming methods based on conventional Central Processing Unit (CPU) computing with Fortran. Considerable room for improvement still remains.Item An analysis of salt welding(2010-05) Wagner, Bryce Hedrick; Jackson, M. P. A.; Cloos, Mark; Hudec, Mike; Steel, Ron; Sen, Mrinal; Peel, FrankSalt can be removed by viscous flow and dissolution to form a salt weld. A complete weld forms when salt is completely removed by these processes. Where salt removal is incomplete, a partial weld forms. Though welds are frequently mentioned in the literature, the details of weld formation and the properties of salt welds are poorly understood. In Chapter 1, I use analytical and numerical models to quantify the role of viscous flow during salt welding. Where salt flow is limited by boundary drag against the salt contacts, evacuation is slow and up to ~50 m of salt will be left behind in a partial weld. Where salt flow is laterally unrestricted, a vanishingly thin (<< 1 m) smear of salt will remain. I conclude that layer-parallel wall rock translation or dissolution must act to remove any remnant salt to create a complete weld. In Chapter 2, I characterize partial welds containing halite and anhydrite on reflection seismic data by treating welds as thin beds. Below the temporal resolution of reflection seismic data, typically ~25-50 m for modern surveys with peak frequencies of ~10-30 Hz, reflections from the upper and lower evaporite contacts converge and interfere to form a single composite reflection. Thus, partial and complete welds are typically indistinguishable using travel-time differences alone. I then use amplitude information from synthetics and seismic examples to estimate remnant evaporite thickness. In Chapter 3, I investigate fluid flow near and through salt welds. I conclude dissolution during boundary flow can remove up to a few meters of salt per million years. Though dissolution plays a volumetrically insignificant but important role in weld formation, as runaway dissolution can create pathways for focused cross-weld migration of subsurface fluids. I identify features that influence cross-weld migration of subsurface fluids and then develop an empirical relationship between weld geometry and the tendency seal or leak hydrocarbons. I find that in the Campos Basin, offshore Brazil, salt welds containing remnant evaporites thinner than ~50 m that are broader than ~25 km2 in area are likely to leak.Item Anthropogenic Disturbance of Western Gray Whale Behavior Off Sakhalin Island, Russia(2013-05-14) Gailey, Glenn AndrewThe western North Pacific population of gray whales (Eschrichtius robustus) is critically endangered of extinction. The population size is estimated to be 131 individuals with 31 reproductive females. Throughout their potential home range, the western gray whale population face several threats to their future survival. On their only known feeding grounds off the northeastern coast of Sakhalin Island, Russia, anthropogenic activity has increased in the past decade due to oil and gas exploration and platform/pipeline construction. This dissertation examines the influences of geophysical seismic surveys (pulse sounds) and platform/pipeline installation (continuous sounds). Each chapter progressively improves upon behavioral models that assess changes in gray whale movements and respirations relative to anthropogenic activity. Theodolite tracking and focal follow methodologies were employed to collect gray whales' movement and respiration information during and in the absence of anthropogenic activity. Spatial, temporal, environmental, and acoustic (pulse and/or continuous) sound levels and non-sound related anthropogenic variables were included as explanatory variables to examine their influence on movement and respiration response variables, such as speed, orientations, dive/surface time, breathing rates, etc. During the 3-D seismic activity, gray whales traveled faster, changed directions of movement less, were recorded farther from shore and stayed underwater longer between respirations as the received sound level exposure increased. During platform/pipeline installations, western gray whales increased their distance from shore with indicators of stress (rapid breathing) and observed to be sensitive to close distance of approach by vessels. No acoustic influence on western gray whale behavior was found during a 4-D seismic survey; however, sample sizes were small in this study to sufficiently detect more subtle to moderate changes in gray whale behavior. These studies illustrate short-term influences anthropogenic activity had on western gray whale behavior which could lead to longer-term responses that may be detrimental to the survival of certain individuals and/or the population. A comprehensive analyses are proposed to increase sample sizes to identify subtle to moderate behavioral changes as well as examine alternative hypotheses to the null hypothesis of no impact used in this dissertation. With the potential to displace individuals/population out of critical feeding habitats needed for their annual survival and the expected increase of anthropogenic activity in the future, this dissertation highlights the importance to monitor and identify problems and suggest alternatives to development/activities that may be impacting this endangered population of gray whales.Item Assessment of Interplate and Intraplate Earthquakes(2012-10-19) Bellam, Srigiri ShankarThe earth was shown in the last century to have a surface layer composed of large plates. Plate tectonics is the study of the movement and stresses in the individual plates that make up the complete surface of the world's sphere. Two types of earthquakes are observed in the surface plates, interplate and intraplate earthquakes, which are classified, based on the location of the origin of an earthquake either between two plates or within the plate respectively. Limited work has been completed on the definition of the boundary region between the plates from which interplate earthquakes originate, other than the recent work on the Mid Atlantic Ridge, defined at two degrees and the subsequent work to look at the applicability of this degree based definition. Others suggested an alternative view of a constant width for the interplate region in recent work at Texas A&M University. The objective of the paper is to determine whether the assumption of a linear width of the region along the tectonic plate boundaries to classify earthquakes as interplate and intraplate earthquakes using accepted statistical criteria provides a better fit to the data than the constant degree definition. There are three types of interplate boundaries defined by the relative movement of the two plates to each other, which further complicates this study. The study used a nonrandom analysis of regions of the different types of boundary to compare the rate and decay of the intraplate earthquakes from a notional centerline for the known boundaries. The study used GIS software and EXCEL for the statistical analysis component of the research work. The results show that a constant width definition provides a number of advantages in determining the relative definition of interplate and intraplate earthquakes when compared to the constant degree definition developed for work on the Mid Atlantic Ridge. Further research is suggested on a randomly selected set of study sites to improve the reliability and quality of the statistical work for each type of the boundary of the tectonic plates.Item Characterization of the Southern High Plains by seismic, gravity, and topographic analysis(2010-12) Hoemberg, Jeffrey; Gurrola, Harold; Zhou, Hua-wei; Leverington, David; Asquith, George B.A topographic database was downloaded from the USGS and applied to several wavelength filtering processes. Seismic data were collected over a period of nine years at seven seismic stations deployed by Texas Tech University across the Southern High Plains, and all available additional data were downloaded from an addition 12 stations in the US Array. This dataset was processed by deconvolution with a subsequent application of an array processing algorithm and then stacked. The processed topographic and seismic data were analyzed in conjunction with gravity data acquired by Ozyavas to observe the presence of shallow crustal structures, midcrustal discontinuities, and the Moho in an attempt to relate these to subtle modern topographic relief across the southern High Plains. Stacks produced from the receiver functions identified five distinct boundaries at: 10km, 18km, Moho, 85km, and 170km. Each boundary was cataloged and mapped spatially. A hinge line trending southwest-northeast observed in the 18km discontinuity lies collinear and appears to have influence over the expression of the Caprock Escarpment. Similarly, an observed ridge in the Moho topography lies collinear to the Matador Arch and may implicate a trend of crustal weakness. The deeper discontinuities at 85km and 170km have structures that mimic features observed in the filtered gravity datasets. Gravity profiles were then reconstructed from Ozyavas, 2004, along three transects of the South Plains and resulting subsurface structure to 200 kilometers was approximated using the discontinuities from seismic as tie points through each line. These cross sections were useful for verification that the inferred layers from the discontinuities were valid results based on observed gravity data.Item Direct in-situ evaluation of liquefaction susceptibility(2014-05) Roberts, Julia Nicole; Stokoe, Kenneth H.Earthquake-induced soil liquefaction that occurs within the built environment is responsible for billions of dollars of damage to infrastructure and loss of economic productivity. There is an acute need to accurately predict the risk of soil liquefaction as well as to quantify the effectiveness of soil improvement techniques that are meant to decrease the risk of soil liquefaction. Current methods indirectly measure the risk of soil liquefaction by empirically correlating certain soil characteristics to known instances of surficial evidence of soil liquefaction, but these methods tend to overpredict the risk in sands with silts, to poorly predict instances of soil liquefaction without surface manifestations, and fail to adequately quantify the effectiveness of soil improvement techniques. Direct in-situ evaluation of liquefaction susceptibility was performed at a single site at the Wildlife Liquefaction Array (WLA) in Imperial Valley, California, in March 2012. The project included a CPT sounding, crosshole testing, and liquefaction testing. The liquefaction testing involved the measurement of water pressure and ground particle motion under earthquake-simulating cyclic loading conditions. The objective of this testing technique is to observe the relationship between shear strain in the soil and the resulting generation of excess pore water pressure. This fundamental relationship dictates whether or not a soil will liquefy during an earthquake event. The direct in-situ evaluation of liquefaction susceptibility approach provides a more accurate and comprehensive analysis of the risks of soil liquefaction. It also has the ability to test large-scale soil improvements in-situ, providing researchers an accurate representation of how the improved soil will perform during a real earthquake event. The most important results in this thesis include the identification of the cyclic threshold strain around 0.02% for the WLA sand, which is very similar to results achieved by other researchers (Vucetic and Dobry, 1986, and Cox, 2006) and is a characteristic of liquefiable soils. Another key characteristic is the 440 to 480 ft/sec (134 to 146 m/s) shear wave velocity of the soil, which are well below the upper limit 656 ft/sec (200 m/s) and an indication that the soil is loose enough for soil liquefaction to occur. The third significant point is that the compression wave velocity of the sand is greater than 4,500 ft/sec (1,370 m/s), indicating that it is at least 99.9% saturated and capable of generating large pore water pressure due to cyclic loading. These three conditions (cyclic threshold strain, shear wave velocity, and compression wave velocity) are among the most important parameters for characterizing a soil liquefaction risk and must all be met in order for soil liquefaction to occur.Item Effect of a discrete three-phase methane equilibrium zone on the bottom-simulating reflection(2016-12) Shushtarian, Arash; Daigle, HughMarine gas hydrates are stable under conditions of low temperature and high pressure in the upper few hundreds of meters below the seafloor in a variety of geological setting. At a discrete horizon where thermodynamically favored phase switches from hydrate to gas, a characteristic seismic reflection referred as the bottom-simulating reflection (BSR) is produced. Furthermore, in sediments with a distribution of pore sizes, the gas and hydrate phases can coexist in pores of different sizes, giving a rise to three-phase equilibrium zone. This three-phase zone causes the BSR to have distinct characteristics that differ from those observed with a discrete phase boundary. The main objective of this thesis is to model the seismic response of a potential three-phase zone at the Walker Ridge Block 313H in the northern Gulf of Mexico. I modeled the BSR arising from this three-phase zone and analyzed the characteristics of the BSR and their relationships to the thickness and phase saturation within the three-phase zone. This was done by determining the elastic properties of the formation via rock physics models and their mathematical convolution with a seismic wavelet to create synthetic seismograms. Results show that the main factor for the intensity of the BSR is the abundance of the free gas in the three-phase zone. Free gas saturation as low as 5% in the three-phase zone is enough to make the BSR visible in synthetic seismograms regardless of the hydrate saturation. Results of this thesis are significant for resource prospecting based on seismic data, drilling hazard identification, as well as the importance of hydrate as a potential source of energy and its influence on the global climate. For seismic prospecting, the presence of a three-phase zone inferred from BSR characteristic indicates the minimum methane flux into the base of the hydrate stability zone, and can be used to infer whether sufficient methane is available to form hydrate. For drilling hazard identification, the BSR characteristic indicates a possible shallower occurrence of gas than would be estimated under the assumption of a discrete phase boundary.Item Feasibility of isotropic inversion in orthorhombic media : the Barrett unconventional model(2016-05) Yanke, Andrew James; Spikes, Kyle; Sen, Mrinal K; Fomel, Sergey BGeophysicists often relegate shale reservoirs as having higher symmetries (e.g., transversely isotropic (TI) or isotropic) than what reality demonstrates. Routine application of TI (or even isotropic) algorithms to orthorhombic media neglects the associated errors because we never know the true model in practice. This thesis evaluates the viability of isotropic post-stack and pre-stack seismic inversion to orthorhombic media using the SEAM Barrett Unconventional Model, the most realistic depositional model to date. The Barrett Model contains buried topography, simulated stratigraphy, and designated reservoir zones with orthorhombic anisotropy. I inverted the Barrett data volume for isotropic elastic property cubes, which I compared to the model volume in each symmetry-plane of an orthorhombic medium. If the stacked seismic data contained only the near offsets, post-stack inversion resolved acoustic impedances that closely matched the true model both within and outside of the reservoir zones at all well locations. Anisotropy most affected the far offsets, so muting them predictably enhanced the post-stack inversion. I maintained all offsets for pre-stack inversion, but a parabolic radon filter eliminated nonhyperbolic behavior (rather than nonhyperbolic moveout analysis) at far offsets. The pre-stack impedance attributes adequately described the vertical heterogeneity of the true model at a cross-validation well, but the inverted values increasingly relied on the initial model with depth. The inverted density estimates experienced notable oscillations relative to the initial model, particularly where steep contrasts in elastic properties occurred. Mismatch of the inverted elastic properties at the well locations can be attributed to noise, thin layering effects, band limitation, steep contrasts in elastic properties, AVO behavior stacked into the data, an inaccurate starting model, and the effects of anisotropy. The most significant sources of error include small-scale reflectivity and comprehensive filtering of nonhyperbolic phenomena. Away from the well locations, the isotropic inversion gave no visual indication of reservoir geobodies, but it sufficiently described the elastic property variations near reservoir mid-sections. Moreover, I showed that the inverted elastic properties differ from their orthorhombic models by no more than 35%. The greatest misfits occurred near reservoir contacts and geobody locations. The computed impedance models in each symmetry-plane have distinctive differences, but isotropic inversion dismisses these variations entirely. I conclude that isotropic inversion should not be a surrogate for orthorhombic methods in data preconditioning and quantitative reservoir characterization.Item Multiazimuth velocity analysis using velocity-independent seismic imaging(2011-05) Burnett, William Andrew, 1983-; Fomel, Sergey B.; Stoffa, Paul L., 1948-Multiazimuth seismic data contains information about how the Earth’s seismic response changes with azimuthal direction. Directional-dependence of the seismic response can be caused by anisotropy or heterogeneity, associated with subsurface features such as fractures, stresses, or structure. Characterizing azimuthal variations is done through velocity analysis, which provides a link between an acquired data set and its image, as well as between the image and subsurface geology. At the stage which conventional velocity analysis is applied, it is difficult to distinguish the geologic cause of observed azimuthal velocity variations. The inability to distinguish the similar effects of anisotropy and heterogeneity leads to positioning errors in the final image and velocity estimates. Regardless of the cause, azimuthally variable velocities require at least three parameters to characterize, as opposed to the conventional single-parameter isotropic velocity. The semblance scan is the conventional tool for seismic velocity analysis, but it was designed for the isotropic case. For multiple parameters, the semblance scan becomes computationally impractical. In order to help address the xiissues of geologic ambiguity and computational efficiency, I develop three methods for multiazimuth seismic velocity analysis based on “velocity-independent” imaging techniques. I call this approach, velocity analysis by velocity-independent imaging, where I reverse the conventional order of velocity estimation followed by image estimation. All three methods measure time-domain effective-velocity parameters. The first method, 3D azimuthally anisotropic velocity-independent NMO, replaces the explicit measurement of velocity with local slope detection. The second method, time-warping, uses local slope information to predict traveltime surfaces without any moveout assumption beforehand, and then fit them with a multiparameter velocity model. The third method, azimuthal velocity continuation, uses diffraction image focusing as a velocity analysis criterion, thereby performing imaging and velocity analysis simultaneously. The first two methods are superior to the semblance scan in terms of computational efficiency and their ability to handle multi-parameter models. The third method is similar to a single multi-parameter semblance scan in computational cost, but it helps handle the ambiguity between structural heterogeneity and anisotropy, which leads to better positioned images and velocity estimates.Item Nonlinear modeling of Texas highway bridges for seismic response-history analysis(2016-12) Prakhov, Vyacheslav Oleksiyovich; Clayton, Patricia M.; Williamson, Eric B., 1968-A recent increase in the number of earthquakes across the state of Texas has raised concerns about seismic performance of highway bridges in the state inventory, the vast majority of which were not explicitly designed to withstand earthquake loading. Potential causes of seismic damage include column shear failure due to low transverse reinforcement rations and non-seismic detailing, girder unseating due to excessive bearing deformation or instability, deck pounding, and others. The objective of the study is to develop bridge numerical models for nonlinear response-history analysis taking into consideration Texas-specific design and detailing practices. Using the models developed, the fragility of Texas bridges can be analyzed and systematically quantified, allowing state highway officials to efficiently identify the bridges most likely to be damaged after an earthquake. Component models for all major bridge parts were developed for this study, including the superstructure, deck joint, bearing, bent, foundation, and abutment. The models were developed based on past experimental, analytical, and numerical work from the literature, accounting for the mass, stiffness, and damping properties of each bridge component. Damage was accounted for using nonlinear hinge models capable of simulating stiffness-degradation and hysteretic behavior based on specific properties and expected limit states of each bridge component. Finally, a MATLAB script was developed to assemble bridge component models into full bridge models depending on user input of geometric and material properties of an individual bridge sample.Item Seismic analysis of the Rocky Mountain Front and Great Plains using transportable array data(2011-05) Castille, Kristopher A.; Gurrola, Harold; Zhou, Hua-wei; Asquith, George B.USArray seismic data along the Rocky Mountain Front and Great Plains was downloaded from the Incorporated Research Institutions for Seismology (IRIS) to map lithosphere boundaries including the Mohorovičić discontinuity (Moho), Hales discontinuity (Hales), and lithosphere-asthenosphere boundary (LAB). Water-level (i.e. prewhitening) deconvolution in the frequency domain was used to filter out the bad stations. The good stations were further improved by cross-correlating and stacking the vertical component of nearby stations (i.e. beamforming) and simultaneously deconvolved to reduce the need for prewhitening and improve the signal-to-noise ratio in the receiver functions. These stacked move-out corrected receiver functions (SMOCRF) were used to interpret depth and Vp/Vs ratios of features in the lithosphere including the Moho, Hales discontinuity, and the LAB, and related these to the geology of the Rocky Mountain Front and Great Plains. The Moho depth across the Rocky Mountain Front and Great Plains correlates well with the previous geological and geophysical work done from the literature with deep signatures along the Rocky Mountain Front, southern granite-rhyolite belt, and Black Hills area, and shallow signature along the southern portion of the Rio Grande Rift. Crustal Vp/Vs ratios are mostly uniform throughout the study area at 1.73 to 1.76, which is average for continental crust. The Hales discontinuity is 80 to 90 km for most of the study area. This correlates well with the original discovery made by A.L. Hales in 1969. Deeper regions on the Hales may be related to orogenic events from the past. It appears that Precambrian features are preserved in the mantle between the Moho and Hales discontinuity. The lithosphere-asthenosphere boundary can be divided into a shallow northern half and deep southern half in the study area. Vp/Vs ratios for each interval do not vary much throughout the entire study area. However, Vp/Vs ratios mapped for the Hales discontinuity show higher values above the Yavapai-Mazatzal transition zone, which is interpreted to be the boundary of this accreted Proterozoic province. Skeptical of the lithosphere-asthenosphere boundary results due to crustal reverberations affecting the quality of data that can occur with P-to-S imaging. Recommend following up with S-to-P receiver functions.Item Seismic Attribute Analysis Using Higher Order Statistics(2009-05-15) Greenidge, Janelle CandiceSeismic data processing depends on mathematical and statistical tools such as convolution, crosscorrelation and stack that employ second-order statistics (SOS). Seismic signals are non-Gaussian and therefore contain information beyond SOS. One of the modern challenges of seismic data processing is reformulating algorithms e.g. migration, to utilize the extra higher order statistics (HOS) information in seismic data. The migration algorithm has two key components: the moveout correction, which corresponds to the crosscorrelation of the migration operator with the data at zero lag and the stack of the moveout-corrected data. This study reformulated the standard migration algorithm to handle the HOS information by improving the stack component, having assumed that the moveout correction is accurate. The reformulated migration algorithm outputs not only the standard form of stack, but also the variance, skewness and kurtosis of moveout-corrected data. The mean (stack) of the moveout-corrected data in this new concept is equivalent to the migration currently performed in industry. The variance of moveout-corrected data is one of the new outputs obtained from the reformulation. Though it characterizes SOS information, it is not one of the outputs of standard migration. In cases where the seismic amplitude variation with offset (AVO) response is linear, a single algorithm that outputs mean (stack) and variance combines both the standard AVO analysis and migration, thereby significantly improving the cost of seismic data processing. Furthermore, this single algorithm improves the resolution of seismic imaging, since it does not require an explicit knowledge of reflection angles to retrieve AVO information. In the reformulation, HOS information is captured by the skewness and kurtosis of moveout-corrected data. These two outputs characterize nonlinear AVO response and non-Gaussian noise (symmetric and nonsymmetric) that may be contained in the data. Skewness characterizes nonsymmetric, non-Gaussian noise, whereas kurtosis characterizes symmetric, non-Gaussian noise. These outputs also characterize any errors associated with moveout corrections. While classical seismic data processing provides a single output, HOS-related processing outputs three extra parameters i.e. the variance, skewness, and kurtosis. These parameters can better characterize geological formations and improve the accuracy of the seismic data processing performed before the application of the reformulated migration algorithm.Item Seismic diffraction imaging methods and applications(2014-05) Decker, Luke Adam; Fomel, Sergey B.; Ren, Kui; Wilson, ClarkSeismic waves can either be reflected or diffracted by subsurface objects depending on the object's geometry. Diffactions can be used to determine details about the small-scale features that generate them, such as karsts, voids, pinchouts, faults, fractures, and salt flanks. Diffraction imaging can have resolution below the typical seismic wavelength. Scattered waves are recorded as significantly lower-energy signal than reflected waves, requiring that diffractions be separated from reflections. I describe three methods of such separation: data-domain plane-wave destruction, Fresnel zone Elimination, and partial-image plane-wave destruction. Once separated, diffractions can be migrated to create a seismic diffraction image and used in velocity analysis. Common-reflection angle migrated diffractions appear flat in dip angle gathers when migrated with correct velocity. I illustrate how this property can be used to determine migration velocity through a process of oriented velocity continuation (OVC). In OVC framework diffraction data are decomposed by slope and migrated over a range of velocities. Velocities corresponding to the flattest slope gathers are picked using semblance as a measure of flatness. This provides an estimate of migration velocity. Stacking gathers corresponding to this chosen velocity generates a seismic diffraction image. Seismic diffraction images provide interpreters with information about small-scale geologic objects that may not be available in conventional images. Scattering features that are interesting for exploration, like voids, caves, fractures, and faults, cause diffractions and can be resolved with better focus in diffraction images than in conventional ones. This is particularly useful with geologically complex carbonate systems. Carbonates are strongly heterogeneous, making them difficult to image with conventional methods. Reservoir porosity is often contained within caves, or small vugs. These features are difficult to characterize with conventional methods because cave reflections have large geometric uncertainties in cave size and location. Velocity analysis of seismic reflection data in carbonates may not highlight vugular porosity particularity well. I illustrate how diffraction images provide improved characterization by highlighting the edges of caves, thus constraining cave geometry, and highlighting more heterogenous zones by measuring the amount of scattering those zones generate.Item Seismic performance of concrete columns reinforced with high strength steel(2014-12) Sokoli, Drit; Ghannoum, Wassim M.Test results are presented from an experimental program carried at the University of Texas at Austin aimed at evaluating the seismic performance of concrete columns reinforced with high-strength steel. Comparisons are made between the performance of columns reinforced with conventional Grade 60 steel, and the higher Grade 80. The high-strength steel used in this study is the result of a recent push in the U.S. to produce higher grade reinforcing bars with relatively high ductility. All steel used satisfied the specifications of ASTM A706. Column specimens were tested under constant axial load and reverse cyclic lateral loading until collapse. Columns performed in a similar manner, indicating that current limits on the yield strength of reinforcing bars in seismic applications could be raised to include Grade 80 A706 bars. Conclusions are drawn with respect to the effects of higher strength reinforcement on, member cracking, drift capacity, plasticity spread, plastic hinge performance, and strain demands on reinforcing bars.Item Seismic retrofit of RC columns with FRP composites and anchorage system(2015-05) Psaros Andriopoulos, Apostolos; Jirsa, J. O. (James Otis); Hrynyk, TrevorResearch on the use of composite materials in structural applications started more than 30 years ago but still remains active. The challenges that accompany those applications are diverse and seem to increase as the variety of applications grows. There are several fiber-reinforced polymer (FRP) systems that have been introduced through the years for strengthening reinforced concrete (RC) structures. Those systems focus on strengthening of slabs, beams and columns. The present study pertains to seismic retrofit of rectangular RC columns. The typical FRP materials used in structural applications are introduced, as well as, how FRP materials become an integral part of the force-resisting system. In addition, analysis work pertaining to a series of strengthened RC columns was conducted and the results were compared to the experimental data. Moreover, deficiencies of typical material models were highlighted. Design guidelines are discussed and recommendations about current design practices are provided. Finally, research gaps and future research recommendations are identified.Item Seismic retrofit of RC columns with FRP composites and anchorage system(2015-05) Psaros Andriopoulos, Apostolos; Jirsa, J. O. (James Otis); Hrynyk, TrevorResearch on the use of composite materials in structural applications started more than 30 years ago but still remains active. The challenges that accompany those applications are diverse and seem to increase as the variety of applications grows. There are several fiber-reinforced polymer (FRP) systems that have been introduced through the years for strengthening reinforced concrete (RC) structures. Those systems focus on strengthening of slabs, beams and columns. The present study pertains to seismic retrofit of rectangular RC columns. The typical FRP materials used in structural applications are introduced, as well as, how FRP materials become an integral part of the force-resisting system. In addition, analysis work pertaining to a series of strengthened RC columns was conducted and the results were compared to the experimental data. Moreover, deficiencies of typical material models were highlighted. Design guidelines are discussed and recommendations about current design practices are provided. Finally, research gaps and future research recommendations are identified.Item Single-crystal elasticity of the lower-mantle ferropericlase (Mg0.92Fe0.08)O(2014-05) Tong, Xinyue; Lin, Jung-FuThis study focuses on investigating the effect of the electronic spin transition of iron on the elasticity of the candidate lower mantle ferropericlase (Mg,Fe)O. This may be relevant to our understanding of the seismic velocity structures of the Earth’s lower mantle. The elastic constants of (Mg₀.₉₂Fe₀.₀₈)O at high-spin (HS) state, low-spin (LS) state, and through the pressure-induced HS-to-LS transition has been measured using both Brillouin Light Scattering (BLS) and Impulsive Stimulated Scattering (ISS). There is a large pressure range in which c₁₁ and c₁₂ exhibit a softening, while c₄₄ does not register such an anomaly. Compared with previously published data of ferropericlase with similar compositions ([Marquardt et al., 2009b], BLS measurement of (Mg₀.₉Fe₀.₁)O and [Crowhurst et al., 2008], ISS measurement of (Mg₀.₉₄Fe₀.₀₆)O), this study provides more reliable elastic constants measurements by taking the advantage of simultaneous measurements on Vp and Vs using both BLS and ISS. Our results show that bulk sound velocity of ferropericlase has a large but smooth softening in the spin transition pressure region. The elastic constants of ferropericlase at the spin transition region and the LS state have been well studied in this thesis, and a relaxation behavior has also been observed in this study. Those two subjects are not well documented in literature. The temperature effect of the spin state transition and its consequential effect on mineral’s elastic properties have not been studied in this project, but further research on this subject will follow. However, even in the room temperature, our results don’t show sudden changes in seismic velocities. Moreover, current theoretical and experimental studies [Sturhahn et al., 2005, Tsuchiya et al., 2006, Lin et al., 2007] indicate that the spin transition takes place over an extended range of depth along an expected lower-mantle geotherm, where sudden changes in compressional and bulk sound velocity are not expected.Item Topographic and Base-level Control on Back-Barrier Lagoon Evolution: West Galveston Bay, TX(2014-12-02) Laverty, Paul HEstuaries are economically and ecologically significant regions that are highly sensitive to external forcing from sea-level rise, storm events, and anthropogenic change. West Galveston Bay (West Bay) is a back-barrier lagoon system located immediately landward of Galveston Island, Texas, and it represents a sub-system of the larger Galveston estuary complex in the Northern Gulf of Mexico (NGOM). Previous studies have documented the evolution of many large estuaries along the NGOM in response to Holocene sea-level rise. However, the prehistory of smaller estuaries like West Bay remain largely overlooked and poorly understood. The primary purpose of this study is to complete a paleoenvironmental reconstruction of West Bay in Texas using geophysical and sedimentological approaches. A total of 30 core samples and more than 160 km of CHIRP seismic data were collected from West Bay and neighboring Chocolate Bay, within which several unique lithofacies and seismic facies were identified. As with other regional studies, the Pleistocene unconformity presents as an impedance change in the seismic profiles, and is most likely the Beaumont Formation. Multiple incised channels were observed on the Pleistocene Unconformity that are most likely seaward extensions of the tributaries that flow into Chocolate Bay, and formed the basal surface of the accommodation available for Holocene infill. Radiocarbon dating of salient lithologic and seismic transitions in a few key cores revealed that several flooding events related to Holocene sea-level rise caused the landward back-stepping and geographic reorganization of depositional environments within West Bay. The first flooding event occurred at ~7,600 Cal. yr. BP caused both fluvial-dominated sedimentation to cease and initiation of estuarine conditions. The next flooding event occurred at ~6,800 Cal. yr. BP tripled the spatially inundated area and created ideal brackish conditions for oyster reef proliferation. This was short lived, however, as reduced salinity and increased turbidity from the paleo-Brazos River that was flowing into the area between ~6,100 and ~4,400 Cal. yr. BP ceased oyster reef production. The final flooding event occurred at ~4,400 Cal. yr. BP, which possibly established the connection between Galveston Bay and West Bay. At this time, an ephemeral tidal inlet formed within the incised channels, and then migrated west until stabilizing in the paleo-Brazos River incised valley as the modern day San Luis Pass. This study reveals how the antecedent topography and sea-level rise controlled the environmental changes within West Bay throughout the Holocene. It also provides insight into how a small coastal system responds to varying rates of sea-level rise. Additionally, it may be useful as a baseline for West Bay for predicting future flooding associated with accelerating rates of sea-level rise.