R-3 Repository :: Browsing by Author "Sawyer, Dale S."

Browsing by Author "Sawyer, Dale S."

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A multi-scale approach to study silicate dissolution: Kinetic Monte Carlo simulations and experimental observations
(2013-08-14) Kurganskaya, Inna; Luttge, Andreas; Dasgupta, Rajdeep; Whitmire, Kenton H.; Sawyer, Dale S.
Dissolution of silicate minerals is an important part of many geological processes taking place on Earth’s surface as well as in the deep crust. Weathering of rocks and soil formation, metasomatic rock alteration by hydrothermal fluids, and diagenetic transformation of sediments are controlled by dissolution reactions. Secondary pore space of natural reservoirs can be significantly altered by dissolution and the subsequent precipitation of clay minerals. As a consequence, the potential storage capacity of natural fuels, carbon dioxide, or radioactive waste, can be affected. In addition, the stability of rocks hosting potentially hazardous materials largely depends on their dissolution rates. The development of computational ab initio and Molecular Dynamics techniques drives the interest to study dissolution reactions at the molecular scale. At the same time, advanced microscopic techniques allow us to study dissolution process at the nm to micron scale and investigate spatio-temporal variations of surface reactivity. The combination of these methods has great potential for tackling fundamental questions of the mechanisms of mineral dissolution. My thesis work presents an integrated multiscale approach to studying the dissolution of silicates. The work consists of three main parts: experimental studies of the dissolving mineral surface at the micron scale, Kinetic Monte Carlo (KMC) simulations at the nanometer scale, and the parametrization of KMC models by ab initio derived activation energies. Muscovite mica and quartz were chosen as template study objects. These two minerals represent “2-dimentional” (phyllosilicates) and 3-dimentional (tectosilicates) crystal structures of silicates as well as “complex” and “simple” chemical bond networks. The first part of my muscovite dissolution studies is based on experimental observations of the reacted surface with vertical scanning interferometry. We quantified the distribution of surface reactivity in terms of surface roughness and mean height levels and also measured the dissolution rate. Additional investigations of the detailed surface structure were done by using atomic force microscopy. KMC simulations of muscovite dissolution constitute the second part of this work. We developed KMC models that simulate the dissolution of mica structures. We varied the number of the basic reaction types in the system and achieved a satisfying match between modeling results and experimental observations. Also, we showed how KMC methods can be used as a tool for testing my hypotheses regarding the role of surface reactions on the overall reaction mechanism. The third part of the work is dedicated to the problems of complexity and parametrization of KMC models. Here, we present four KMC models of quartz dissolution that vary by their complexity level. The capabilities of the models to predict experimentally observed dissolution features were shown for prism, rhombohedral, and pinacoid quartz faces. The simulation results demonstrate the role of the topological state in the recognition of key surface sites. From this study we derived basic dissolution mechanisms for the three faces.
Automatic characterization of the spatial statistics of topography using geostatistical methods
(2002) Kesavan, Sunitha; Sawyer, Dale S.
An automatic geostatistical method of analyzing spatial characteristics of topography is presented. Anisotropy in spatial continuity is modeled by estimating the range of the directional semivariograms. Spatial characteristics of topography are defined by orientation of the semi-major axis, length of the semi-major axis and length of the semi-minor axis of the anisotropy model ellipse. Orientation of the ellipse gives the average orientation of the linear features. Aspect ratio of the ellipse estimates the degree of lineation of features. Area of the ellipse determines the roughness of the topography. The automatic geostatistical topography characterization method was applied to land topography from Western US and sea-floor topography from the Ross sea, Antarctica. The method was able to characterize the spatial patterns of topography from Western US. The method was used to separate highly lineated regions on the Antarctic sea floor from areas with less prominent or no lineations.
Characterizing shallow aquifers with wave-propagation based geophysical methods: Imaging and attribute analysis
(1999) Bradford, John; Sawyer, Dale S.; Talwani, Manik
As the results of seismic reflection and ground penetrating radar (GPR) studies become more prevalent as input for quantitative groundwater and engineering studies, it is important to evaluate traditional approaches to data processing and analysis. Where conventional methods fail it is necessary to investigate and/or develop non-traditional approaches to data analysis. I present five stand-alone studies that are focused on characterizing shallow aquifers using seismic reflection and GPR data processing and analysis. Each of the projects involves a new approach to data analysis either through alternative processing strategies that are not widely applied in environmental studies or development of new processing methods and/or algorithms. The first two studies are focused on seismic reflection imaging problems that arise in the shallow environment. I first present a detailed discussion of the errors that can result from conventional normal-moveout (NMO) processing, and the application of pre-stack depth migration (PSDM) to improve image accuracy. Second, I apply dip-moveout (DMO) processing to a data set from the Puget Sound. DMO is rarely applied in environmental studies, but can improve velocity analysis and image quality where there are dipping layers or scattering events. The final three studies are focused on attribute analysis of GPR and seismic reflection data in direct detection studies. Over the past 10--15 years, direct detection has been used successfully in the energy industry to identify oil and gas reserves from exploration scale seismic reflection data, but is a new approach to the analysis of GPR and shallow seismic reflection data. Direct detection studies use reflected wave attributes such as amplitude, frequency content, and phase to estimate material properties. I first present a detailed discussion of GPR amplitude vs. offset (AVO) analysis for direct detection of free phase non-aqueous phase liquid contaminants (NAPLs). The analysis is not straightforward and requires careful consideration of electromagnetic dynamic properties. Second, I present a shallow seismic case study where a predictable AVO response was detected. Finally, I present a new wavelet decomposition and time-frequency representation, and illustrate applications in GPR attenuation analysis for NAPL detection and lithology characterization.
Crustal deformation across the Galicia Bank of offshore Iberia from seismic reflection data: Processing, interpretation, and reconstruction
(2002) Knoll, Edward Tyler; Sawyer, Dale S.
The Iberia Margin is an excellent example of a passive rift. Multi-Channel Seismic (MCS) data consisting of the Line 14 reflection profile from the 1997 Iberia Seismic Experiment were processed and interpreted. Enhanced processing attenuated pervasive water-bottom multiple noise. MCS data image an extensional terrain that includes the Ocean-Continent Transition (OCT). The Moho is imaged locally. Extended crust was restored to an unextended state to quantify deformation. Horizontal strain tends to increase seaward along dip; the average strain is 46%. Crustal-thickness data indicate an average crustal thickness of 9.9 km. With certain assumptions regarding the observability of extension, the presence of 'pure shear' exclusively, and initial crustal thickness, there is a major discrepancy between the observed average crustal thickness and the average crustal thickness predicted by observed strain. The only satisfactory explanation is that crust has been removed by asymmetrical extension (simple shear).
Crystal Dissolution Kinetics: Linking Surface Processes at the Solid-Solution Interface over Multiple Length-Scales
(2007) Vinson, Michael David; Luttge, Andreas; Sawyer, Dale S.; Lee, Cin-Ty A.; Whitmire, Kenton H.
This thesis presents a multiple-scale experimental study of mineral dissolution kinetics, utilizing direct measurement of crystal surface morphology in great detail to determine rates and mechanisms acting at the reactive solid-solution interface. The overall approach uses primarily vertical scanning interferometry (VSI) to analyze threedimensional crystal surface morphological change and quantify rates of dissolution. Integration of VSI with atomic force microscopy (AFM), theoretical kinetic models, and thermodynamic calculations has permitted the recognition of rate-controlling processes and mechanisms, thus strengthening our ability to link dissolution kinetics over a broad range of length and time scales. The motivation for this thesis arises from an incomplete understanding of how molecular-scale surface processes, acting at the solid-solution interface, control large-scale natural dissolution phenomena. Mineral dissolution is a fundamental geologic process that exerts control over a number of significant geochemical events which can affect both man and the environment over a broad range of spatial and temporal scales. At the Earth surface, rates of dissolution are largely surface-controlled, and thus influenced by the threedimensional nature of the crystal surface. The goals of this thesis involve improving overall understanding of dissolution rate-scaling issues by investigation of crystal surface dissolution kinetics, identification ofrate-controlling mechanisms. This thesis reports investigations into the dissolution kinetics of calcite, rhyolite and uraninite over a range of far-from-equilibrium laboratory conditions. The results presented within this work demonstrate that: 1. Monomolecular "rough" step retreat controls the overall rate of calcite crystal dissolution, which in turn can be inhibited by impurity adsorption at a level dependent on the physical and chemical properties of the adsorbing impurity and the presence of carbonate in solution. 2. Heterogeneous retreat of volcanic glass phases control overall rhyolite dissolution rate and the steady-sate release of ions into solution, which in turn may be influenced by the formation of a surface reprecipitation phase. 3. Dissolved carbon species influence the steady-state dissolution uraninite, although this dissolution fails to produce resolvable surface-normal retreat. In total, this original work constructs a clearer understanding of the kinetics at the reactive solid-solution interface and reveals how dissolution phenomena can scale across time and space.
Current absolute plate motion from seismic anisotropy and hotspot tracks; bounds on the latitudinal shift of the Hawaiian hotspot during formation of the Hawaiian island and seamount chain
(2013-12-06) Zheng, Lin; Gordon, Richard G.; Lenardic, Adrian; Symes, William W.; Sawyer, Dale S.
Hotspots, the volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere, can serve as a reference frame to track the motion of the plates relative to the mantle beneath the asthenosphere. The application of the hotspot reference frame, however, is limited by the relative hotspot motion ranging from a few mm a-1 [Morgan, 1971; Duncan, 1981; Muller et al., 1993; Koivisto et al. 2013] to 80 mm a-1 [Raymond et al., 2000]. This dissertation aims to evaluate the hotspot reference frame. In the first part, I estimate the plate motion relative to the sub-asthenospheric mantle from seismic anisotropy data [Kreemer, 2009]. Prior studies based on seismic anisotropy assume that errors in the azimuths inferred from shear-wave splitting are uncorrelated. In this dissertation, I show that the residuals of azimuths inferred from shear-wave splitting beneath any one tectonic plate are strongly correlated with other residuals from the same plate. I account for these correlations in an inversion for absolute plate angular velocity by adopting a two-tier analysis of plate absolute velocities. First I find the pole of rotation and confidence limits for each plate individually. Then I perform a global inversion in which each plate is represented not by multiple individual estimates of the orientation of seismic anisotropy but by a single best-fitting pole and confidence limits. In the second part, I estimate plate motion from two hotspot data-sets: T57, consisting of 57 trends of hotspot tracks distributed on ten major plates [Morgan and Phipps Morgan, 2007]; and HS3, consisting of 11 trends and 2 propagation rates of hotspot tracks distributed on four major plates [Gripp and Gordon, 2002]. I test the assumption of uncorrelated errors in hotspot trend, following the same approach as previously used for seismic anisotropy data. I estimate the best-fitting angular velocities after removing the correlated errors within plates in T57 hotspot data-set. Volcanic age dates used in HS3 tend to be younger than true ages due to the bias inherent in K-Ar measurements. Therefore, the volcanic propagation rates tend to be too high. I use the difference between an astrogeochronologic-based, and a K-Ar-based, geomagnetic reversal time scale as a proxy to recalibrate the K-Ar age dates, which reduces the volcanic propagation rates of the Hawaii hotspot track and the Society hotspot track by 8% and 4% respectively. The global set of best-fitting angular velocities estimated from seismic anisotropy data in the first part, are compared with those estimated from hotspot data-sets in the second part. In the third part, I test the hotspot mobility from the magnetic anomaly data due to seafloor spreading. I estimate the location of the Pacific paleomagnetic pole of anomaly 20r (44 Ma B.P.) by analyzing the skewness of marine magnetic anomalies. Then I reconstruct this paleomagnetic pole in the Pacific hotspot reference frame [Andrew et al., 2006; Koivisto et al., 2013], and compare it with prior paleomagnetic pole at the similar age in the Indo-Atlantic hotspot reference frame [Besse and Courtillot, 2002].
Effects of Stress on Failure Behavior of Shallow, Marine Muds from the Northern Gulf of Mexico
(2014-06-18) Zhao, Xin; Dugan, Brandon; Morgan, Julia K.; Sawyer, Dale S.
Direct simple shear (DSS) experiments on mud samples from 4.3-13.4 meters below sea floor (mbsf) document that stress impacts soil strength and pore pressure genesis during failure. As burial depth increases from 7.3 to 13.4 mbsf, cohesion decreases from 12.3 to 6.5 kPa and internal friction angle increases from 18° to 21°. For the same depth increase, peak shear strength increases from 30 to 63 kPa. For a specimen from 11.75 mbsf, an increase in maximum consolidation stress from 45 to 179 kPa results in an increase in the shear-induced pore pressure from 29 to 150 kPa. The normalized shear strength at peak shear, however, decreases from 0.37 to 0.25 over this consolidation range. Our results indicate that compaction induces a positive feedback on pore pressure genesis. This feedback suggests an increase in failure potential during burial at shallow depth. To further understand the physical controls on this behavior, we complete DSS experiments on resedimented samples to erase stress history and sediment fabric. For the resedimented samples, cohesion is 3.2 kPa and internal friction angle is 24°. An increase in maximum consolidation stress from 40 to 254 kPa results in an increase in the peak shear strength from 14 to 91 kPa and an increase in the shear-induced pore pressure from 22 to 203 kPa; however, the normalized shear strength at peak shear decreases from 0.32 to 0.28. Resedimented samples show similar strength and failure behavior to intact samples. By constraining pore pressure and strength response to initial stress state and fabric, we are beginning to gain better insight on slope failure dynamics. Thus, this study may provide constraints on submarine landslide risks by investigating impact of stress and sedimentary fabric on soil strength and pore pressure genesis during shear failure.
Estimating subsurface structure through gravity and gravity gradiometry inversion
(1999) Condi, Francis J.; Sawyer, Dale S.; Zelt, Colin A.
We use gravity to estimate rifted margin deep structure with an inversion method that links parameters in the shallow parts of the model to those in the deep parts through an isostatic, uniform extension model. The method provides for variable weighting of prior information, estimates densities and shapes simultaneously, and can be used in the presence and absence of deep seismic data. Synthetic tests of sensitivity to noise indicate that the isostatic extension constraint promotes the recovery of the short wavelength Moho topography, eliminates spatial undulations in deep structure due to noise in the data, and increases the range of acceptable recovered models over no isostatic extension constraint. In application to real data from the Carolina trough, the method recovers models that exhibit anomalously high density in the hinge zone area, apparently anomalously thick crust, and anticorrelation of subcrustal lithospheric densities with crustal densities. The first two features are observed in deep seismic studies. The latter is consistent with melting model predictions. We then present a unified view of the traditional gradiometric observables---differential curvature, horizontal gradient of vertical gravity, and vertical gradient of vertical gravity, in terms of invariants of the full gradient tensor, and examine their ability to recover subsurface structure through an efficient inversion method. Results of synthetic tests performed on selected complex bodies and noise free data indicate differential curvature and the horizontal gradient of vertical gravity do as well as the full tensor in recovering subsurface structure. In the presence of noise, we find that a mass constraint promotes recovery of smooth models and may be more appropriate than finite difference smoothing. Differential curvature appears to be a useful observable when inverted alone and as an early search technique in full tensor inversion.
Infrared spectroscopy of Mars
(1999) Kirkland, Laurel Ellyn; Sawyer, Dale S.
When measured with sufficient spectral range, resolution, and signal-to-noise ratio, nearly every mineral has a unique infrared spectral signature. However, determining which minerals are present on Mars using infrared spectroscopy has proven to be very difficult. The goal of this work is to examine complicating factors inherent to spacecraft-based infrared spectral measurements of Mars, and to determine methods to extract mineralogical information from spectra that cover the wavelength range 0.77 to 50 mum. On Earth, infrared spectra of an unknown mineral or gas can be measured under controlled conditions. However, a spacecraft spectrometer measures Mars through both atmospheric gases and aerosols, and at varying viewing geometries. Spectra of the surface of Mars have very subtle variations, so examining them requires well-calibrated spectra of excellent quality, and extended spectral range. These combined effects greatly complicate interpretations. The work presented here details a straightforward method to remove effects of varying viewing geometry on near-infrared spectra of Mars, using 1989 Phobos 2 ISM spectra. Next, it details the recovery and calibration of the 1969 Mariner Mars IRS data set, and presents IRS spectral evidence for goethite on Mars. Finally, a method is developed to utilize night spectra to examine the aerosol mineralogy, followed by a discussion of the importance of accounting for the aerosol re-emission when utilizing day measurements to examine surface mineralogy. This work utilizes spectra from all five infrared spectrometers flown to Mars. It addresses a range of issues, but the unifying theme is how to extract mineralogic information from the spectra. The results show that the most important spectral criteria for determining mineralogy from spacecraft infrared spectra are an extended spectral range, high spectral resolution, and high signal-to-noise ratio. Here, an extended spectral range is defined as coverage of at least two of the three infrared spectral regions: reflected (∼0.8--3 mum), overtone (∼3--7 mum), and fundamental (∼7--50 mum). Spectra with low spectral resolution, low spectral range, or low signal-to-noise ratio allow different spectral type units to be mapped, but such data sets do not provide enough information to determine uniquely the mineral phases present.
Modeling the Dynamic Change of Air Quality and its Response to Emission Trends
(2013-09-04) Zhou, Wei; Cohan, Daniel S.; Griffin, Robert J.; Sawyer, Dale S.; Pinder, Robert W
This thesis focuses on evaluating atmospheric chemistry and transport models’ capability in simulating the chemistry and dynamics of power plant plumes, evaluating their strengths and weaknesses in predicting air quality trends at regional scales, and exploring air quality trends in an urban area. First, the Community Mutlti-scale Air Quality (CMAQ) model is applied to simulate the physical and chemical evolution of power plant plumes (PPPs) during the second Texas Air Quality Study (TexAQS) in 2006. SO2 and NOy were observed to be rapidly removed from PPPs on cloudy days but not on cloud-free days, indicating efficient aqueous processing of these compounds in clouds, while the model fails to capture the rapid loss of SO2 and NOy in some plumes on the cloudy day. Adjustments to cloud liquid water content (QC) and the default metal concentrations in the cloud module could explain some of the SO2 loss while NOy in the model was insensitive to QC. Second, CMAQ is applied to simulate the ozone (O3) change after the NOx SIP Call and mobile emission controls in the eastern U.S. from 2002 to 2006. Observed downward changes in 8-hour O3 concentrations in the NOx SIP Call region were under-predicted by 26%–66%. The under-prediction in O3 improvements could be alleviated by 5%–31% by constraining NOx emissions in each year based on observed NOx concentrations while temperature biases or uncertainties in chemical reactions had minor impact on simulated O3 trends. Third, changes in ozone production in the Houston area is assessed with airborne measurements from TexAQS 2000 and 2006. Simultaneous declines in nitrogen oxides (NOx=NO+NO2) and highly reactive Volatile Organic Compounds (HRVOCs) were observed in the Houston Ship Channel (HSC). The reduction in HRVOCs led to the decline in total radical concentration by 20-50%. Rapid ozone production rates in the Houston area declined by 40-50% from 2000 to 2006, to which the reduction in NOx and HRVOCs had the similar contribution. Houston petrochemical and urban plumes largely remained in a strong VOC-sensitive regime of ozone formation and maintained high Ozone Production Efficiency (OPE: 5-15).
Multicomponent seismic data analysis in the tau-p domain
(1997) Jiang, Zerong; Sawyer, Dale S.
I develop a number of new methods for performing slant stacking and its variants suitable to the processing of ocean bottom seismograph (OBS) data. I develop two versions of the discrete Radon transform (DRT) pair, a generalization of slant stacking, which can handle data unevenly spaced in both offset (x) and ray parameter (p). The discrete Radon transform matrix consists of two parts: a scaling matrix and a phase shift matrix. The elements in the phase shift matrix determine the amounts of the shift of given frequencies for stacking. I develop an iterative approach to perform velocity stacking, a parabolic variant of slant stacking, in the time domain. Invertibility of the transform is secured by iteration over the residual energy. A better focused version of the velocity profile is achieved. I extend conventional slant stacking of single component data to multicomponent data by performing a "vector" slant stack. The vector slant stack is performed by first transforming each component of the data, then combining the components in the $\tau$-p. This transform produces a vector field in $\tau$ and p. A color scheme using RGB intensity respectively to represent the vertical, radial and transverse components in either the x-t or the $\tau$-p domain is developed for displaying three component seismic data. I develop a technique to separate P-wave and S-waves arriving at the receiver in the vector $\tau$-p domain. I have designed an algorithm to decompose a vector common-p trace into P, SV, and SH traces. The result will be three sections in the $\tau$-p domain which can be inverse transformed to the x-t domain. (Abstract shortened by UMI.)
Nature and Evolution of Deep Water Carbonate Drifts in the past 3 Million years, Inner Sea of the Maldives Archipelago, Equatorial Indian Ocean
(2013-07-24) Lopez, Karem; Droxler, Andre W.; Anderson, John B.; Sawyer, Dale S.
The Maldives atolls, the very top of one of the largest modern carbonate platforms, occupy the central and largest part of the Chagos-Laccadives ridge located in the equatorial Indian Ocean. In the central part of the archipelago, the large atolls form tw
Non-destructive optical imaging system for enhanced lateral resolution
(2008-01-29) Luttge, Andreas; Sawyer, Dale S.; Conrad, Pamela G.; Rice University; United States Patent and Trademark Office
In some embodiments, an optical imaging system comprises a non-destructive optical device that obtains information concerning a target object and a X,Y positioning system that is capable of positioning one or both of the target object and the optical device to pre-determined offset locations more closely spaced than the obtainable resolution of the optical device. A first “base” image is produced and then overlapping additional images may be produced by the positioning one or both of the target object and the optical device to the pre-determined locations. The first image and the additional images may be combined to produce a single combined image that contains inherently more information than the first image or any of the additional images alone. The combined image then may be digitally restored and enhanced to produce an image with a greater resolution than the optical device yields.
Numerical Modeling of the Formation and Evolution of Basement-Involved Structures in Wyoming
(2014-01-21) Zhang, Jie; Morgan, Julia K.; Anderson, John B.; Akin, John Edward.; Dugan, Brandon; Sawyer, Dale S.
The Wyoming foreland is composed of basement-involved structures and intermontane basins formed during the Laramide Orogeny. Based on their sizes, structures in this area can be categorized into primary uplifts and secondary folds. Tectonic models suggest the primary uplifts form by sliding the crustal slabs along a deep-seated, large-scale regional detachment in the lower crust, and rotating the basement wedges along listric primary faults. The secondary folds are located close to and trend sub-parallel to the adjacent primary structures, suggesting a causative or correlative relationship between the two, although this connection has not been firmly established through field and seismic investigations. I carry out numerical simulations using both the finite element method (FEM) and discrete element method (DEM) to explore the structural evolution of these secondary basement-involved structures. The first study investigates the Laramide-age Sheep Mountain anticline, located in the eastern Bighorn Basin of Wyoming, using comparative FEM and DEM simulations. The kinematic and mechanical results of the two simulations are similar, thus verifying the methodological comparison. Differences in the geometric details, however, provide important perspectives on the capabilities of the two methods. The mechanical properties defined through this comparative study are then employed in DEM simulations that investigate the relationships between primary and secondary structures during the displacement of large crustal slabs along primary thrust faults. My results show that the displacements and geometries of the primary faults have great impact on the distributions and throw values of the secondary faults. For shallow primary faults with limited regional shortening, the numbers and the displacements of secondary faults are evenly distributed across the basin, with no preference in dip direction. For steep primary faults with significant regional shortening, conjugate faults form early and subsequently cluster into groups. I also explore the influences of initial sedimentary thickness, sedimentary mechanical stratigraphy, and syn-tectonic sedimentation on the distribution of secondary faults. Thicker Pre-Laramide deposits allow more secondary faults to form early during deformation, absorbing the horizontal shortening within the sedimentary layer. The presence of weak shale layers in the sedimentary section allows numerous small faults to form, and limits the depth of all the faults. Syn-tectonic sedimentation reduces the number of secondary faults that form in the basinal area, and displacements along those faults are very small. In this case, most of the deformation is accommodated by the faults located above the ramp take-off location, at the edge of the syn-tectonic deposits.
Seismic imaging with traveltime and waveform inversion: Naga Thrust and Fold Belt, India
(2009) Jaiswal, Priyan; Zelt, Colin A.; Sawyer, Dale S.; Gordon, Richard G.; Hirasaki, George J.
I demonstrate the utility of traveltime and waveform inversion in depth imaging of seismic data with the help of two 2-D multichannel seismic lines, Reg-07 and PO-03, shot perpendicular to the trend of the Naga Thrust and Fold Belt (NTFB), India. I use both lines to demonstrate that a) a velocity model from traveltime inversion is suitable for pre-stack depth migration (PSDM) and can effectively serve as a starting model for frequency-domain full-waveform inversion; b) both PSDM and waveform inversion yield interpretable depth images but a combination of the two best describes the geology; and c) there still exists untested and unexploited hydrocarbon potential in the NTFB. Using the Reg-07 data I establish a working methodology for combining traveltime inversion with waveform inversion and PSDM. The results are validated using a nearby well. Using the PO-03 data I first demonstrate the advantages of combining traveltime inversion with PSDM for depth imaging; the combined method is referred to as unified imaging. Unified Imaging simultaneously yields a velocity model and a depth image that are consistent with each other. The velocity model from unified imaging is validated using an in-line well. The depth image from unified imaging reveals the presence of a triangle zone along PO-03 that was previously unknown and could be promising for exploration. Waveform inversion using the velocity model from unified imaging reveals the presence of a complex conjugate fault system in the supra-thrust along PO-03 which was also previously unknown and could also be promising for exploration. Traveltime inversion estimates a velocity model that is representative of the large scale features of the subsurface. This makes traveltime inversion a necessary first step regardless of the final choice of imaging--PSDM or waveform inversion. While PSDM uses the traveltime model as a whole for estimating a reflectivity image, waveform inversion enhances the resolution of a part of the traveltime model to yield a detailed acoustic property map. Even though the data and model requirements for PSDM are less stringent than for waveform inversion, waveform inversion appears to be resolving structural features that are imaged inadequately by PSDM.
Structural and tectonic interpretation of deep seismic reflection data offshore Spain and Portugal: A tectonic rifting model
(2001) Unger, Michael Rhodes; Sawyer, Dale S.
A portion of new seismic reflection/refraction data collected over the Iberia margin were processed and interpreted, resulting in the recognition of two previously unknown normal faults in the deep crust. These faults, named Q and R, formed during the Triassic-Cretaceous rifting of Pangea, and formation of the Atlantic basin. Previous studies have shown a third surface, the low-angle S reflector, in the area. S has previously been interpreted as a detachment surface or as a velocity interface. A model is proposed where extension was accommodated along Q, R and S during the rifting of Pangea. R and S acted as detachment surfaces as the hangingwall block moved westward. Late in the rifting process, the geometry of R and S was altered by motion of underlying serpentinized mantle material. This upwelling of the mantle controlled the shape of Sin three dimensions. Total extension across the margin is estimated at 1.67.
Tectonics of the West Iberia continental margin from seismic reflection data
(2005) Henning, Alison Teagan; Sawyer, Dale S.
Continental rifting is a fundamental component of the plate tectonic cycle. The West Iberia passive margin is a classic example of a nonvolcanic rifted margin. The West Iberia margin contains an enigmatic north-south ridge of serpentinized peridotite located within the ocean-continent transition. Interpretation of multichannel seismic data and tectonic subsidence analyses suggests that the ridge is located within a broad zone of exhumed mantle that has been serpentinized. This implies that seafloor spreading does not immediately follow continental breakup. Where the peridotite ridge is well-developed, it parallels a deeply-penetrating, west-dipping normal fault. Hydrodynamic circulation drove seawater down this fault close to the beginning of seafloor spreading and caused a concentration of serpentinization at its base. This water-driven process of formation accounts for the variability of the ridge along strike. Prestack depth migration of a 340 km long seismic reflection profile across the margin served as the basis for stratigraphic interpretation. The proximal margin displays horsts and grabens, with 1--2 km thick synrift deposits from Early Cretaceous (Valanginian) rifting. The deep water margin displays rotated blocks with distinct internal seismic patterns. These blocks formed during the final Cretaceous rifting event that led to continental breakup, and contain earlier Valanginian synrift deposits as part of the rotated blocks, thus providing evidence of two separate rifting stages along this profile. A large mantle-penetrating fault located seaward of the last rotated block of continental crust provides evidence for a third and final Cretaceous rifting event that may have been coeval with early seafloor spreading. Two independent estimates of crustal thickness along this line indicate stretching factors of 50% on the proximal margin (corresponding to a continental crustal thickness of ∼16 km), increasing to 100% in the deep water. Plate tectonics is one of the most important concepts that Earth Scientists can convey to the public. While this concept is often presented at the middle school level in Texas, the appropriateness of teaching plate tectonics to middle school students has been questioned. We present data that suggest that middle school students grasp the abstract concepts of plate tectonics as well as college students.
The rifting history of the Newfoundland-Iberia conjugate margins: A geodynamic analysis
(1994) Tett, David L.; Sawyer, Dale S.
Rifting between Newfoundland and Iberia occurred in two distinct phases--the first late Triassic to early Jurassic, the second late Jurassic to early Cretaceous--culminating in the creation of the North Atlantic Ocean. A dynamic modelling method was used to examine the implications of multiple phases of rifting on the development of the Newfoundland-Iberia conjugate margins. The models predicted a lack of magmatism on these margins, and suggested that extension was significantly greater in the second rifting phase than in the first; these predictions agree with geological observations. The models could not predict the existence of highly thinned continental crust on both conjugate margins, however. In addition, a set of generic models roughly based on the Newfoundland and Iberia margins suggested that, where two rift phases occur, the site of the original rift usually will not be favored for extension when stretching resumes.
Three-dimensional geometries of rifting on a hyperextended margin - Interpretation of seismic reflection profiles from the Deep Galicia Basin, Iberia
(2010) Borgmeyer, Amy L.; Sawyer, Dale S.
Our study utilizes a pseudo-3D grid of 2D, depth-migrated seismic profiles in order to provide new constraints on rifting within the Deep Galicia Basin. 3D analysis shows that faults strike within 10° of north, indicating east-west directed rifting. Three distinct structural domains are identified on the east-west oriented profiles. In addition to an exhumed mantle domain, two crustal domains are distinguished by their different faulting styles and thinning. Restored crustal thickness (9-14 km) within the intracrustal fault domain (IFD) is close to the current thickness of the Galicia Bank crust (15-20 km), implying that the observed faults within the IFD were the first to form after the formation of the Galicia Bank. Restored crustal thickness within the detachment fault domain (DFD) is less than in IFD, yielding 3-5 km thickness. This suggests that the DFD either experienced an additional generation of faulting compared to the IFD, or was extended by a different mechanism, e.g. rolling-hinge-style rifting.

Browsing by Author "Sawyer, Dale S."

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