A synthetic seismic gather showing amplitude versus offset can be analyzed by the interpretive geophysicist to predict rock properties useful in oil exploration. Reflection coefficients derived from measured well log data are convolved with a Ricker wavelet to create a synthetic seismic trace. The Zoeppritz equations describe the propagation of an acoustic wave across an interface between two viscous media of different acoustic impedances with respect to increasing offset angle. The Aki-Richards linear approximation is used to create a synthetic seismic gather with offset angles up to fifty degrees. This gather is compared to a synthetic gather created using commercially available software.

The Oligocene-Miocene collision between Panama and South America significantly influenced ocean currents, global climate, and species diversification. Intraplate deformation of the Panama Block also played an important role in the evolution of this tectonic system, but is not well understood. A high-resolution gravity survey, coupled with geologic observations, was conducted in north-central Panama to better constrain the processes responsible for the Isthmus' modern configuration. Approximately 110 gravity stations were collected from Colón to Nombre de Dios, Panama and merged with existing data. Subsequently, four 2.5-D gravity models were produced to constrain the geometry of the Gatun-Chagres Basin using different sedimentary densities (1.8, 2.0, and 2.2 g/cm3) to produce a realistic range of basin thicknesses. Overall, models with an average basin density of 2.0 g/cm3 are most consistent with offshore seismic profiles and field evidence, suggesting basin thickness is ~3.0-3.5 km. Previous seismic reflection data and geochemical analyses of Miocene arc volcanic rocks delineate a zone of extension in the Panama Canal Region, and gravity analysis from this study supports this hypothesis. Field evidence of multiple NW-facing normal faults suggests that they separate the basin from uplifted arc basement rocks east of the Canal, resulting in a 60 mGal gravity gradient. Beneath the basin, gravity models indicate ~5-10 km of crustal thinning. 3-D reconstruction of the 2.5-D models show a northward thickening basin and two depocenters that correspond to the Rio Indio and Toro facies of the Chagres Formation. This analysis suggests two directional extension of the Gatun-Chagres Basin; an east-west direction corresponding to the initial formation of the basin, and a modern northwest-southeast direction. To the northeast, gravity modeling indicates that there is a ~150 m-thick, Cretaceous-Holocene sedimentary basin present from Portobelo to Nombre de Dios. Sedimentary units in the western part of this basin exhibit large-scale open folds, which may indicate a transition from extensional to compressional tectonics east of the Panama Orocline Apex. The ongoing collision between South America and the Panama Block also fractured the crust creating zones of extension in central Panama. Overall, gravity modeling suggests that low-density sedimentary rocks extend across the Isthmus and south of the Gatun-Chagres Basin. Such results are consistent with the idea that the Panama Canal Region formed a young marine connection between the Caribbean Sea and Pacific Ocean. / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester 2015. / October 19, 2015. / Basin, Geophysics, Gravity, Modeling, Panama, Tectonics / Includes bibliographical references. / David W. Farris, Professor Directing Thesis; James F. Tull, Committee Member; Stephen Kish, Committee Member; Seth Young, Committee Member.

The goal of this project is to combine gravity measurements with geologic observations to better understand the "Big Bend" of the San Andreas Fault (SAF) and its role in producing hydrocarbon-bearing structures in the southern Central Valley of California. The SAF is the main plate boundary structure between the Pacific and North American plates and accommodates ≈35 mm/yr of dextral motion. The SAF can be divided into three main parts: the northern, central and southern segments. The boundary between the central and southern segments is the "Big Bend", which is characterized by an ≈30°, eastward bend. This fault curvature led to the creation of a series of roughly east-west thrust faults and the transverse mountain ranges. Four high-resolution gravity transects were conducted across locations on either side of the bend. A total of 166 new gravity measurements were collected. Previous studies suggest significantly inclined dip angle for the San Andreas Fault in the Big Bend area. Yet, our models indicate that the San Andreas Fault is near vertical in the Big Bend area. Also gravity cross-section models suggest that flower structures occur on either side of the bend. These structures are dominated by sedimentary rocks in the north and igneous rocks in the south. The two northern transects in the Carrizo plains have an ≈-70 mgal Bouguer anomaly. The SAF has a strike of ≈315° near these transects. The northern transects are characterized by multiple fault strands which cut marine and terrestrial Miocene sedimentary rocks as well as Quaternary alluvial valley deposits. These fault strands are characterized by ≈6 mgal short wavelength variations in the Bouguer gravity anomaly, which correspond to low density fault gouge and fault splays that juxtapose rocks of varying densities. The southern transects cross part of the SAF with a strike of 285°, have a Bouguer anomaly of ≈-50 mgal and are characterized by a broad 15 mgal high. At this location the rocks on either side of the fault are Proterozoic - Cretaceous metamorphic or/and plutonic rocks. Previous work based on geologic mapping hypothesized the existence of a shallow, low angle Abel Mountain Thrust in which crystalline rocks were thrust over Miocene sedimentary rocks, near Apache Saddle. However, gravity models indicate the crystalline rocks are vertically extensive and form a positive flower structure bounded by high angle faults. Also, based on the thickness of fault adjacent sedimentary cover, the gravity models suggest a minimum exhumation of 5-6 km for crystalline rocks in the south. Assuming exhumation began with the switch from the transtensional San Gabriel Fault to transpressional San Andreas Fault at approximately 5 Ma, this indicates exhumation rates of 1 km/Ma. Overall, the broad gravity highs observed along the southern transects are due to uplift of basement rocks in this area. / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester 2015. / November 9, 2015. / Includes bibliographical references. / David W. Farris, Professor Directing Thesis; James F. Tull, Committee Member; Stephen Kish, Committee Member.

New and existing geochemical and Sr-isotopic data are used to characterize the composition and time-space distribution of Laramide and younger calc-alkaline to alkaline igneous rocks in central Colorado. The study is focussed on the $\sim$36.7-31 Ma Thirtynine Mile volcanic field, a suite of shoshonitic rocks that forms the bulk of the Central Colorado alkaline province. Various petrochemical characteristics suggest generation of Thirtynine Mile mafic rocks involved melting of LIL- and HFSE-enriched lithospheric mantle, perhaps phlogopite-bearing lherzolite. Subsequent crystal fractionation appears capable of explaining diversification of the suite. The Thirtynine Mile suite is LIL- and HFSE-enriched relative to time-contemporaneous high-K calc-alkaline rocks of the San Juan volcanic field, but shares some geochemical similarities with Laramide shoshonitic rocks of the northeastern Colorado mineral belt. General petrochemistry and spatial distribution of calc-alkaline and shoshonitic volcanic rocks in the region may be consistent with a subduction origin, but no unambiguous evidence is available to confirm this. / Geochemical and Sr-isotopic evidence confirms tuff occurrences in the southern Denver basin are Wall Mountain Tuff ($\sim$36.7 Ma). Previous suggestions that the Wall Mountain Tuff is closely related to the Mount Princeton batholith are not supported by new data, and the origin of the tuff remains unknown. Combined petrologic, geochemical, and Sr-isotopic data confirm that the $\sim$33.7 Ma Badger Creek Tuff is closely related to intracauldron tuff and a resurgent(?) pluton at the Mount Aetna volcanic center. Tuff at Buffalo Peaks is probably not related to Badger Creek Tuff. Geochemical and Sr-isotopic data suggest that andesitic tuff, lahar debris, and andesite flows at Buffalo Peaks are closely related, but the source of the volcanic suite remains unknown. Tuff in the Howard paleovalley and in the southeastern Thirtynine Mile volcanic field is probably Fish Canyon Tuff derived from the San Juan volcanic field. Sparse late-Tertiary rocks within the study area include shoshonite, trachyte, latite, and siliceous rhyolite and granite. / Source: Dissertation Abstracts International, Volume: 55-08, Section: B, page: 3211. / Major Professors: Stephen A. Kish; Paul C. Ragland. / Thesis (Ph.D.)--The Florida State University, 1994.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Geology and Geophysics, 1964. / Vita. / Includes bibliographical references. / by Hilda Cid-Dresdner. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Geology and Geophysics, 1968. / Bibliography: leaves 64-67. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Geology and Geophysics, 1969. / Bibliography: leaves 19-20. / M.S.

<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>

Massachusetts Institute of Technology. Dept. of Geology and Geophysics. Thesis. 1966. Ph.D. / Includes bibliographies. / Ph.D.

Thesis. (Ph.D.) Massachusetts Institute of Technology. Dept. of Geology and Geophysics, 1954. / Vita. / Bibliography: leaves 290-298. / by John Christopher Hagen. / Ph.D.