<p> Roat&aacute;n Island is the largest of the Bay Islands of Honduras. These islands form an emergent crest off the Caribbean coast of Honduras called the Bonacca Ridge. The Bartlett Trough to the north and subsequent Bonacca Ridge were likely formed due to the transform fault system of the Motagua-Swan Islands Fault System. This fault system forms the tectonic plate boundary between the North American and Caribbean plates. Although the timing and kinematics are poorly constrained, the Bay Islands and the Bonacca Ridge were likely uplifted due to transpression along this left-lateral strike-slip system. With limited regional exposures along the adjacent tectonic boundary, this study aimed to present a structural interpretation for Roat&aacute;n. This new interpretation is further explained through regional considerations for a suggested geologic history of the northwestern Caribbean. </p><p> In order to better constrain the kinematics of uplift and exhumation of Roat&aacute;n Island, structural, gravity, and magnetic surveys were conducted. Principal attention was directed to the structural relationship between the geologic units and their relationship to one another through deformation. Resulting geologic cross-sections from this study present the metamorphic basement exposed throughout the island to be in a normal structural order consisting of biotite schist and gneiss, with overlying units of chlorite schist, carbonate, and conglomerate. These units have relatively concordant strike and dip measurements, consistent with resultant magnetic survey readings. Additionally, large and irregular bodies of amphibolite and serpentinite throughout the island are interpreted to have been emplaced as mafic and ultra-mafic intrusions in weakness zones along Early Paleogene transform system fault planes. </p><p> The interpretation and suggested geologic history from this study demonstrate the importance of transpressive tectonics both local to Roat&aacute;n and regionally throughout geologic history. Consideration of this interpretation will help to further constrain regional studies over the northwestern Caribbean.</p>

<p> The seismic attribute High-Frequency Absorption (HFA) is a method of evaluating the absorptive properties of rocks as nonstationary wavelets pass through the substrate. This technique is used today as a direct hydrocarbon indicator, where it should be used as a diagnostic tool in conjunction with several other geophysical and geological processes for the delineation of hydrocarbon reservoirs. Understanding the absorptive properties of target reservoirs and correlating their geophysical aspects to geologic properties, courtesy of well logs, may allow us to interpret patterns between hydrocarbon saturation and HFA on local reservoir scales. The ability to estimate hydrocarbon saturation can significantly affect the risk evaluations of potential prospects and further increase our rate of success when wildcatting or developing fields. Analysis shows that in this particular project, proper data, such as neutron-density logs, are seldom run in the wells of this area, thus making estimation of water/hydrocarbons very difficult and very inaccurate. Other complications include the resolution of seismic data compared to well log data. Due to these obstacles, high-resolution correlations of HFA to hydrocarbon saturation proved to be unsuccessful. However, association of proven vs. false prospects showed very high correlations to HFA signatures.</p>

<p> Previous work conducted by Kushiyama (2010) identified a relative gravity profile with an abnormal anomaly across a normal fault. The relative gravity should have decreased when crossing from the upthrown side to the downthrown side. Additional relative gravity data were collected and incorporated with the existing data to create an improved gravity anomaly map. The map shows that the gravity generally increases from the southwest to the northeast in the study area. In two areas where profiles cross the fault at nearly a perpendicular angle, the fault is clearly visible and interpretable from the gravity data. However, along Chris Road, that is not the case. This is most likely caused by an underlying salt ridge (Varvaro, 1958). The mobilization of this salt upwards through more dense strata might be the cause of the low gravity effect of the upthrown side of the fault along Chris Road.</p><p>

<p> A 3D seismic volume across the campus of California State University, Long Beach images the Alamitos Heights fault, a splay of the Newport-Inglewood fault zone (NIFZ). The Alamitos Heights fault is a zone that strikes approximately N55&deg;W, dips on average 80&deg;SW, and bounds the northeast extent of the Seal Beach oil field structure. It plays a role in the complex evolution of the Newport-Inglewood fault zone within the Los Angeles sedimentary basin, which is closely related to timing and trapping mechanisms of nearby oil fields. Its origin and development may be related to fault steps or discontinuities along the main NIFZ. Seismic evidence suggests the Alamitos Heights fault may have originated as a transtensional feature during the Miocene before transitioning to its current transpressional stress regime.</p>

<p> This thesis examines different methods of communicating volcanic hazards to the population of Flagstaff, Arizona using the results of a recent lava flow hazard assessment of the nearby San Francisco Volcanic Field (SFVF). Harburger (2014) determined that given a lava flow originating in the SFVF, there is a statistical probability that it will inundate the city of Flagstaff or even originate from a vent within the city limits. Based on the recurrence rates for the most recent eruptions (3 x 10-4/year), the probability of lava flow inundation in Flagstaff is 1.1 x 10-5 per year. </p><p> This study considers the effects of three different communication methods on participants&rsquo; perceived risk. The methods were administered through a questionnaire and included a statement of probability of lava flow inundation per year, a statement of probability over a 100 year period, and an interactive lava flow map derived from the results of the lava flow hazard assessment. Each method was followed by questions gauging level of concern. Questionnaires were administered to 213 Flagstaff residents over a two week period in February 2015. </p><p> Results showed that levels of concern, rated from 1 (not concerned) to 5 (very concerned), varied based on each method of communication. The method with the greatest effect on perceived risk was the simulated lava flow map, while the first method with a one year odds resulted in a statistically lower mean rating of concern. It is suggested that the best way to change levels of perceived risk when communicating lava flow hazards includes a combination of comprehensible odds and visual aids. Further studies could also include visualization of the entire eruption scenario, including time scales and other volcanic hazards, which may have more effect on concern than a simplified visualization of lava flows.</p>

<p> The lateral "corners" where Kamb and Whillans Ice Streams (KIS and WIS) discharge into the Ross Ice Shelf share common geometries and ice mechanical settings. At both corners of the now-stagnant KIS outlet, shear margins of apparently different ages confine regions with a relatively flat, smooth surface expression. These features are called the "Duckfoot" on the northern, right-lateral side and the "Goosefoot" on the other. It has been suggested, on evidence found in ice internal layers, that the flat ice terrains on KIS were afloat in the recent past, at a time when the ice stream grounding line was upstream of its present location. The overdeepening in the bed just upstream of the KIS grounding line supports this view of the past geometry. </p><p> The right-lateral margin at the outlet of the currently active WIS, the location of Subglacial Lake Englehardt (SLE), appears to have many similarities with the right lateral margin of KIS, though with a less developed looking inboard margin. This paper presents a mechanical analysis using surface and bed topography and velocity datasets comparing the Duckfoot flat ice terrain with the terrain around Subglacial Lake Englehardt. At both locations mechanical thinning along shear margins and lows in the bed topography redirects basal water routing towards the features. Here, I consider the history of these features and their role in ice stream variability by comparison of the relict and modern features and via numerical modeling of ice shelf grounding and ungrounding in response to variations in ice flow. </p><p> We propose two scenarios for the development of flat ice terrains/subglacial lakes at the outlets of ice streams. In the first, development of a lake in the hydraulic potential low along a shear margin forces a margin jump as shearing develops along the inboard shore of the margin lake. This thesis presents evidence for an inboard (relative to the main outboard shear margin) zone of shear along the inboard shoreline of SLE, suggesting that subglacial lakes along shear margins are capable of facilitating shear margin jumps. In the second, grounding line advance around a relative low in the bed, creating adjacent margins along the lakeshores, forms a remnant lake. Discerning which of these scenarios is appropriate at the KIS outlet has implications for understanding the history of the ice stream grounding line. </p><p> An ice flow model is used to place these local conditions in a regional context by studying the effect of internal perturbations, such as ice rise stagnation or inward margin jumps, on grounding line position. Bathymetry is important in determining ice stream flow in the ways that might not be otherwise realized in 1-D flow model studies. In the numerical modeling experiments, grounding line advance across the KIS outlet is mediated by the overdeepening in the bed and proceeds not in the direction of ice flow but transverse to flow. This finding adds complexity to both a flowline view of grounding line migration and the theory that grounding lines are unstable in the presence of inward sloping bed topography.</p>

<p> Possible sea-floor spreading anomalies are indentified in marine magnetic surveys conducted in the eastern Gulf of Mexico. A symmetric pattern of lineated anomalies can be correlated with the geomagnetic time scale using previously proposed opening histories for the Gulf of Mexico basin. Lineated magnetic anomalies are characterized by amplitudes of up to 30 nT and wavelengths of 45-55 km, and are correlatable across 12 different ship tracks spanning a combined distance of 6,712 km. The magnetic lineations are orientated in a NW-SE direction with 3 distinct positive lineations on either side of the inferred spreading ridge anomalies. The magnetic anomalies were forward modeled with a 2 km thick magnetic crust composed of vertically bounded blocks of normal and reverse polarity at a model source depth of 10 km. Remnant magnetization intensity and inclination are 1.6 A m^-1 and 0.2&deg; respectively, chosen to best fit the magnetic observed amplitudes and, for inclination, in accord with the nearly equatorial position of the Gulf of Mexico during Jurassic seafloor spreading. The current magnetic field is modeled with declination and inclination of and 0.65&deg; and 20&deg; respectively. Using a full seafloor spreading rate of 1.7 cm/yr, the anomalies correlate with magnetic chrons M21 to M10. The inferred spreading direction is consistent with previous suggestions of a North-East to South-West direction of sea-floor spreading off the west coast of Florida beginning 149 Ma (M21) and ending 134 Ma (M10). The opening direction is also consistent with the counter-clockwise rotation of Yucatan proposed in past models.</p>

<p> The depositional environment of the middle to late Eocene Oberlin sand of Northwest Oberlin Field and Pilgrim Church Field in central Allen Parish, Louisiana, was investigated. The depositional environment of the Oberlin sand has been interpreted from observations of spontaneous potential log signatures, conventional core reports, paleontological reports, shape of isochore maps, coherency extraction attribute, amplitude extraction attribute, and multiple seismic and subsurface cross sections. Focus is centered on the juxtaposition of component sand bodies and their proximity to the interdistributary and prodelta environments. Sand bodies include distributary channels, distributary mouth bars, crevasse subdeltas and shelfal bars and are interpreted to be the products of lower deltaic and shelf processes. The results of this study are based on seismic analysis, display techniques and subsurface maps calibrated to well logs, models, and recognition criteria of modern and ancient depositional environments previously described in the regional literature. The integration of all available data provides an objective and systematic approach detailing the origin, lateral extent, geometry and architecture of the Oberlin sand in the lower deltaic plain and shelf environments. The results of this study may be applicable to similar age sands on trend with the study area. Understanding of sand component types of the lower deltaic and shelf environments is vital to exploration success and development optimization of hydrocarbon bearing reservoirs.</p>

Thesis (Ph.D.)--University of California, Santa Barbara, 2006. / (UnM)AAI3208727. Adviser: Bruce Luyendyk. Source: Dissertation Abstracts International, Volume: 67-03, Section: B, page: 1333.

Thesis (Ph.D.)--Columbia University, 2006. / (UMI)AAI3237336. Advisers: Dennis Hayes; Garry Karner. Source: Dissertation Abstracts International, Volume: 67-10, Section: B, page: 5625.