University of Texas Institute for Geophysics Technical Reports

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The University of Texas Institute for Geophysics (UTIG) research staff present their research findings/results/ scientific summaries as peer-reviewed publications in various journals or at scientific meetings which often have distribution limitations. Research summaries/results may also be presented as technical reports and made public. Some of these are made available here.


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Now showing 1 - 20 of 127
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    UTIG's approach to managing polar aerogeophysical data in the field: philosophy and examples from fixed wing and helicopter surveys, 27 pages, 2022.
    (University of Texas Institute for Geophysics, 2022-12) Ng, Gregory; Lindzey, Laura; Young, Duncan; Buhl, Dillon; Kempf, Scott; Beem, Lucas; Roberts, Jason; Greenbaum, Jamin; Blankenship, Don D.
    This report documents UTIG’s approach to managing aerogeophysical data in the field. This approach to fieldwork has taken shape in the course of over 20+ years of polar campaigns based out of over 10 Antarctic stations. Aerogeophysical survey is not simply about the act of making measurements and observations. A key component of conducting surveys is managing data as it is collected and providing feedback for quality control. We want to document that institutional knowledge for the benefit of researchers who are continuing in this work as well as for the users of our data. While this document focuses on data management in the field, we start by providing the context for a typical aerogeophysical campaign and describe how the work is broken up amongst teams. We then discuss the philosophy behind field data processing, with a focus on what the goals are for preliminary processing and how it differs from the final products. With that motivation, we describe how the Base Operations team typically meets those goals, along with case studies of how we have applied this approach when based at a variety of stations and field camps, with the differing logistical challenges imposed by each. Companion documents focusing on instrumentation and airborne operations are forthcoming.
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    The PLATES 2020 Atlas of Plate Reconstructions (500 Ma to Present Day), PLATES Progress Report No. 396-1220
    (Institute for Geophysics, 2021-01-29) Lawver, L.A.; Norton, I.O.; Dalziel, I.W.D.; Davis, M.B.
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    The PLATES 2018 Atlas of Plate Reconstructions (550 Ma to Present Day), PLATES Progress Report No. 394-0219
    (Institute for Geophysics, 2019-02-19) Lawver, L.A.; Norton, I.O.; Dalziel, I.W.D.; Gahagan, L.M.
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    KRT1/LGV1 Season Field Report
    (Institute for Geophysics, 2017-04-09) Lindzey, L.; Quartini, E.; Buhl, D.; Blankenship, D.; Richter, T.; Greenbaum, J.; Young, D.
    Description of a dual helicopter aergeophysical survey from Jang Bogo Station, Terra Nova Bay, Antarctica that took place in 2016-2017, supported by UTIG graduate student assistants and engineers. Ice penetrating radar and laser altimetry over David Glacier and Nansen Ice Shelf were collected by one helicopter as part of the KRT1 campaign, while gravity data was collected over Nansen Ice Shelf as part of the LGV1 campaign on a second helicopter.
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    Opening of the Central North Atlantic: Revised Seafloor Spreading Isochrons and Tectonic Map from Geosat Data (Paleoceanographic Mapping Project Progress Report No. 39-0888)
    (Institute for Geophysics, 1988) Mueller, R. Dietmar; Scotese, Christopher R.; Sandwell, David T.
    Plate reconstructions for the opening of the Central and North Atlantic were made by combining Geosat altimetry and magnetic anomaly data. Geosat deflection of the vertical (horizontal gravity) data, which reflect the short wavelength basement topography of the ocean floor allowed us to construct a much improved map of fracture zones m the Central and North Atlantic. The fabric of prominent fracture zones, as interpreted from Geosat deflection of the vertical data, was utilized to constrain the fits of corresponding magnetic anomaly lineations by using an Evans and Sutherland 3-D graphics computer system. For example, we have used the trace of the Charlie-Gibbs Fracture Zone to better constrain the spreading history between the North American and Eurasian plate. Movements of smaller plates such as in the Canadian Arctic and the western Mediterranean were tied to the relative motion of the major plates by applying a hierarchical plate analysis technique. Our tectonic model served as a base to construct a self-consistent isochron chart of the Central and North Atlantic ocean floor.
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    Depth and Age in the South Atlantic (Paleoceanographic Mapping Project Progress Report No. 40-0888)
    (Institute for Geophysics, 1988) Nuernberg, Dirk
    A significant flattening of the relation between depths and age of ocean floor older than 80 Ma can be explained by assuming that the oceanic lithosphere acts as a thermal boundary layer on top of a viscous upper mantle. In the past, uncertainties of age, of sediment thickness and of bathymetry limited the predictions about this relationship. In this study, recent data from the South Atlantic have been averaged into half by half degree elements, so that the relationship between depth and age can be studied in detail. We constructed a high resolution isochron chart for the South Atlantic using the latest available compilation of magnetic anomaly data and satellite altimetry data. The most recent sediment thickness map is used to correct bathymetry for sediment loading in order to obtain the accurate depth to basement We have plotted the corrected basement depth versus age for the entire South Atlantic as well as for distinct areas. The depth/age relationship is presented as contours about the mode enclosing approximately two thirds of the data. In the South Atlantic, the ocean floor subsides with the square root of age on crust younger than 80 Ma. Beyond 80 Ma depths flatten significantly with age. Moreover, a change of the depth/age relationship for opposite flanks as well as with latitude is obvious, which might be related to small scale convection in the upper mantle.
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    Atlas of Mesozoic and Cenozoic Plate Tectonic Reconstructions 1987 (Paleoceanographic Mapping Project)
    (Institute for Geophysics, 1987) Scotese, Christopher R.; Gahagan, Lisa M.; Ross, Malcolm I.; Royer, Jean-Yves; Mueller, R. Dietmar; Nuernberg, Dirk; Mayes, Catherine L.; Lawver, Lawrence A.; Tomlins, Robin L.; Newman, Jerry S.; Heubeck, Christoph E.; Winn, J. Kyle; Beckley, Lila; Sclater, John G.
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    Plate Tectonic Reconstructions of the Cretaceous and Cenozoic Ocean Basins (Paleoceanographic Mapping Project Progress Report No. 34-1287)
    (Institute for Geophysics, 1987) Scotese, Christopher R.; Gahagan, Lisa M.; Larson, Roger L
    In this paper we present nine reconstructions for the Mesozoic and Cenozoic, based on the sea-floor spreading isochrons published by Larson et al. (1985). The purpose of this study was: 1) to determine if the isochrons drawn by Larson et al. (1985) could be refitted to produce a self-consistent set of plate tectonic reconstructions, 2) to use the areas of apparent mismatch between magnetic isochrons as a focus for further investigations, and 3) to test the capabilities and accuracy of interactive computer graphic methods of plate tectonic reconstruction. In general, Tertiary and Late Cretaceous isochrons could be refitted reasonably well; however, closure errors were apparent in the vicinity of the Bouvet and Macquarie triple junctions. It was not possible to produce Early Cretaceous reconstructions that were consistent with the isochrons drawn by Larson et al. (1985). In this paper we also propose that the Late Cretaceous and early Tertiary plate reorganizations observed in the Indian Ocean were the result of the progressive subduction of an intraTethyan rift system.
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    Tectonic Fabric Map of the Ocean Basins from Satellite Altimetry Data (Paleoceanographic Mapping Project Progress Report No. 32-1287)
    (Institute for Geophysics, 1987) Gahagan, Lisa M.; Royer, Jean-Yves; Scotese, Christopher R.; Sandwell, David T.; Winn, J. Kyle; Tomlins, Robin L; Ross, Malcolm I.; Newman, Jerry S.; Mueller, R. Dietmar; Mayes, Catherine L.; Lawver, Lawrence A.; Heubeck, Christoph E.
    Satellite altimetry data provides a new source of information on the bathymetry of the ocean floor. This study used the SEAS AT and GEOSA T altimetry data to produce a global map which displays the tectonic fabric of the ocean basins. The data were processed and interpreted as discrete data points. The result is a map which describes the outlines of various tectonic features through a series of lineations corresponding to the gravity anomalies associated with the features. The uniformity of the satellite coverage enables this map to serve as a global database of greater resolution and continuity than currently provided by ship-track data. This map permits the extension of the physical limits of many tectonic features well beyond what was previously known, particularly in the southern oceans. For instance, various fracture zones, such as the Ascension, Tasman, and Udintsev fracture zones, can be extended much closer to their respective continental margins. The tectonic fabric map reveals many features which are not apparent on global bathymetric charts. These features include extinct ridges, minor fracture zone lineations, and seamounts. In several areas, especially on aseismic plateaus and along continental margins, the map displays broad gravity anomalies whose origin, though unknown, may relate in some way to basement structure. It is obvious that the tectonic fabric displayed by this map has much potential for future, in-depth studies.
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    Phanerozoic Paleogeography Map (Paleoceanographic Mapping Project Progress Report No. 33-1287)
    (Institute for Geophysics, 1987) Winn, Kyle; Scotese, Christopher R.
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    Evolution of the Antarctic Continental Margins (Paleoceanographic Mapping Project Progress Report No. 31-1287)
    (Institute for Geophysics, 1987) Lawver, Lawrence A.; Royer, Jean-Yves; Sandwell, David T.; Scotese, Christopher R.
    With the exception of the Pacific facing margin of West Antarctica between Thurston Island and the tip of the Antarctic Peninsula, all of the continental margins of Antarctica are either rifted passive margins or sheared transform margins. The exception was a convergent margin where subduction was active from prior to the breakup of Gondwanaland until very recently. Starting in the southwestern Weddell Sea which rifted as part of a back -arc basin connected with back-arc spreading in the Rocas Verdes Basin of southern South America during the Middle to Late Jurassic ( -170 Ma), the continental margins of Antarctica seem to young clockwise. A sheared margin along the Explora Escarpment between 25°W and 10°W connected the southwestern Weddell Sea rifting with contemporaneous rifting in the Mozambique Basin. This resulted in a Middle Jurassic rifted passive margin along Dronning Maud Land. East of the Gunnerus Ridge at 35°E, Sri Lanka and India rifted off of Antarctica sometime between 129 Ma and 118 Ma. Rifting between Australia and Antarctica, stretching in the Ross Sea Embayment and rifting between the Campbell Plateau--Chatham Rise and Marie Byrd Land, all started about 95±5 Ma. The convergent margin on the Pacific margin of the Antarctic Peninsula stopped active subduction in the west at about 50 Ma, with the most recent subduction about 5 Ma off the South Shetland Islands. The only presently active continental margin on the Antarctic Continent is a short section of left lateral transform fault along the tip of the Antarctic Peninsula. Very young volcanism in the Ross Sea region may indicate that a new continental margin is in the initial stages of formation.
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    Crustal Structure of the South Florida Bank Derived from Ocean Bottom Seismometer Refraction Profiles (Final Report on Refraction Experiments that were part of the South Florida Bank Study)
    (Institute for Geophysics, 1984) Ebeniro, Joseph O.; O'Brien, William P. Jr.
    In March 1982, six seismic refraction lines, 70 to 90 km long, were shot in the southeastern Gulf of Mexico using the advanced Texas digital ocean bottom seismometers. Five lines were on the South Florida bank region in water depths of less than one kilometer and one was in water depth of about 2.4 km off the northern coast of Cuba. After data reduction, first arrival picks were made and least-square lines were fitted to the picks to obtain the apparent velocities and intercept times for the layers. Using these values, flat-layer crustal models have been computed. The two most dam inant refractors have apparent velocities of 5.6-5.9 km/sec and 6.2-6.6 km/sec. The top of the 5.6-5.9 km/sec layer varies in depth from 2-5 km below the sea surface and is interpreted to represent the crystalline basement. Alternatively, this layer may constitute a carbonate section with velocities indistinguishable from crustal velocities. Basement rock, at a depth of 3.4 km, was overlain by various carbonate facies in a well in the Pinellas County arch. In the South Florida bank area, the deepest refractor observed has an apparent velocity of about 7.5 km/sec at a depth of 25 km. The absence of any interpretable mantle arrivals in these long refraction profiles on the platform suggests that the crust underlying the South Florida bank platform is continental in nature. Possible mantle arrivals were seen at the ends of the line off the northern coast of Cuba (apparent velocities and depths: 7.7 km/sec and 21 km at the northern end and 8.4 km/sec and 26 km at the southern end), suggesting a mantle that dips strongly to the south towards Cuba. Similar crustal thickness has been observed in a refraction profile just northwest of this line. This deep crust structure compliments the earlier shallow crust structures for this area.
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    Report to Landmark Graphics Corporation, University Partnership Program
    (Institute for Geophysics, 1989) Stoffa, Paul L.
    Seismic processing requires accurate knowledge of the earth's velocity structure to properly image and interpret multi-fold seismic data. Conventional analysis methods are based on determining the best fit hyperbolas to seismic travel-times, T, as a function of source-receiver offset, X, in CMP gathers. The results of this analysis are the two-way normal-time, and the stacking velocity for each event analyzed. If the source-receiver offsets are not too large compared to the reflector depth, the stacking velocities can be equated to the RMS velocity. From knowledge of the RMS velocity and two-way normal times above and below a zone of interest, the interval velocity can be determined. Even if the earth is truly one-dimensional, i.e., velocity varies only as a function of depth, errors arise from the departure of the actual travel-times trajectories from the assumed T(X) hyperbola and the departure of the stacking velocity from the RMS velocity. These errors are in addition to the uncertainties involved in determining both the stacking velocity and the two-way normal-times from limited offset, band limited data in the presence of coherent and random noise. An alternative interval velocity analysis method can be implemented if we first perform a plane wave decomposition of the seismic data. By transforming the data to the the domain of intercept time, t, and horizontal ray parameter, p, velocity analyses can be performed exactly for a one-dimensional earth model without the need for intermediate quantities such as the stacking and RMS velocities. Workstation technology, such as the LandmarkTM, can then be used to do this velocity analysis interactively. For example, the original seismic data are plane wave decomposed on a remote computer, e.g., a Cray, and are then transferred either via ethernet or tape to the Landmark for interpretation. The interpretation is done directly in the ?-p domain by interactively 3 defining ?-p travel time curves and superimposing these curves on the ? -p data. Once reasonable agreement is achieved, the plane wave data are NMO corrected in the ?-p domain and then redisplayed. (The NMO corrections can be to two-way time or to depth.) The interpretation procedure is now repeated in the NMO domain to refine the velocity depth structure. The data can be windowed in time and ray parameter prior to analysis and the window changed during the interpretation process. The parameters determined directly by the interpreter are the interval velocity and the thickness and/or two-way normal-time of each layer. No approximations are required and all source receiver offsets are implicitly included in the analysis.
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    Computer Programs to Translate LIS Format, Verical Seismic Profile (VSP) Data to SEG-Y Exchange Data Tape Format
    (Institute for Geophysics, 1988-12-23) Wiederspahn, Mark; Phillips, Joseph D.
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    Southeast Asia (Paleoceanographic Mapping Project Progress Report No. 44-0888)
    (Institute for Geophysics, 1988) Lawver, Lawrence A.; Lee, Tung-Yi
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    Tectonic History and New Isochron Chart of the South Pacific (Paleoceanographic Mapping Project Progress Report No. 43-0888)
    (Institute for Geophysics, 1988) Mayes, Catherine L.; Sandwell, David T.; Lawver, Lawrence A.
    We have developed an internally consistent isochron chart and a tectonic history of the South Pacific using a combination of new satellite altimeter data and shipboard magnetic and bathymetric data. Highly accurate, vertical deflection profiles (1-2 µrad), derived from 22 repeat cycles of Geosat altimetry, reveal subtle lineations in the gravity field associated with the South Pacific fracture zones. These fracture zone lineations are correlated with sparse shipboard bathymetric identifications of fracture zones and thus can be used to determine paleo-spreading directions in uncharted areas. The high density of Geosat altimeter profiles reveals previously unknown details in paleo-spreading directions on all of the major plates. Magnetic anomaly identifications and magnetic lineation interpretations from published sources were combined with these fracture zone lineations to produce a tectonic fabric map. The tectonic fabric was then used to derive new plate reconstructions for twelve selected times in the Late Cretaceous and Cenozoic. This is the first time that the tectonic history of the entire South Pacific has been studied as a whole. From our reconstructions, we estimated the former location of the spreading centers in order to derive a new set of isochrons (interpreted lines of equal age on the ocean floor). We believe that the use of new Geosat altimeter data in combination with a multi-plate reconstruction has led to a major improvement in our understanding of South Pacific tectonics. There are three times of important changes in the tectonic history of the South Pacific. Just prior to Chron 34 (84.0 Ma) spreading initiated between Marie Byrd Land and the New Zealand block (the Campbell Plateau and the Chatham Rise). Spreading in the southwest Pacific was occurring along two different spreading centers between Chron 34 (84.0 Ma) and Chron 25 (58.9 Ma): the Pacific-Antarctic Spreading Center to the west and the Pacific-Bellingshausen Spreading Center· to the east at around the time of Chron 21 (49.4 Ma), the eastern and western spreading centers began spreading about a common pole of rotation. In addition, the Pacific-Antarctic Spreading Center broke through old crust to the north, transferring a piece of crust created at the Pacific-Aluk spreading center to the Antarctic plate. The next major change in the South Pacific occurred between Chron 7 (25.8 Ma) and Chron 5 (10.6 Ma) when spreading initiated at the Galapagos Spreading Center and the East Pacific Rise was reoriented from spreading in a northwesterly direction to spreading in a northeasterly direction.
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    Preliminary Tectonic Fabric Chart of the Indian Ocean (Paleoceanographic Mapping Project Progress Report No. 42-0888)
    (Institute for Geophysics, 1988) Royer, Jean-Yves; Sclater, John G.; Sandwell, David T.
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    Evolution of the Eastern Indian Ocean since the Late Cretaceous Contraints from Geosat Altimetry (Paleoceanographic Mapping Project Progress Report No. 41-0888)
    (Institute for Geophysics, 1988) Royer, Jean-Yves; Sandwell, David
    We propose a new model for the tectonic evolution of the Eastern Indian Ocean from the Late Cretaceous to the present. Two types of data are used to improve previously-published reconstructions. First, reinterpreted seafloor magnetic anomalies, between Australia and Antarctica and in the Wharton basin, provide new constraints on spreading rates and the timing of major reorganizations. Second, vertical deflection profiles (i.e. horizontal gravity anomaly), derived from 22 repeat cycles of GEOSAT altimeter data, reveal the tectonic fabric associated with fracture zones. These new GEOSAT data provide tight constraints on paleo-spreading directions. For example, three prominent fracture zones can be traced from south of Tasmania to the George V Basin, Antarctica providing an important constraint on the relative motions of Australia and Antarctica through the Late Eocene. In addition, the GEOSAT profiles are used to locate the conjugate continental margins and continent-ocean boundaries of Australia and Antarctica, as well as the conjugate rifted margins of Kerguelen Plateau and Broken Ridge. Based on a compilation of magnetic anomaly data from the Crozet Basin, the Central Indian Basin, the Wharton Basin and the Australian-Antarctic Basin, ten plate tectonic reconstructions are proposed. Reconstructions at chrons 5 (11 Ma), 6 (21 Ma), 13 (36 Ma) and 18 (43 Ma) confirm that the Southeast Indian Ridge behaved as a single plate boundary since chron 18. The constraints from the GEOSAT data provide an improvement in the fit of the Kerguelen Plateau and the Broken Ridge at chron 20 (46 Ma). The opening of the Australian-Antarctic Basin from break-up to chron 24 requires a decoupling between the northern and southern provinces of the Kerguelen Plateau. Finally, the model for the relative motions of India, Australia and Antarctica is consistent with the emplacement of the Ninetyeast Ridge and the Kerguelen Plateau over a fixed hotspot.