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    Widths of imbricate thrust blocks and the strength of the front of accretionary wedges and fold-and-thrust belts
    ( 2021-12-03) Garrett Ito
    Besides the large-scale wedge shape itself, the most prominent structural feature of accretionary wedges and foldand- thrust belts is the common pattern of imbricate thrust faults. This study illuminates the fundamental mechanical processes and material properties controlling the width of the crustal blocks bounded by major thrusts using analytical solutions of stress as well as two-dimensional finite-difference models. The numerical models predict that the initial width w0 of a thrust block is set when that block first forms at the very front of the wedge. The width is found to subsequently decreases approximately in proportion to the mean horizontal strain needed for an ideally triangular-shaped Coulomb wedge with a critical taper. Block width is proportional to the thickness H of the incoming, accreting sediment. A key quantity that influences the normalized initial block width w0/H is the distance L forward of the frontal thrust needed for the net horizontal force from shear on the base of the incoming sediment to balance the net force on the frontal thrust. It is within this distance where stress in the incoming sediment is substantially elevated and thus where the new frontal thrust forms. Results show that L/H and, correspondingly, w0/H increase with increasing sediment friction angle ϕ, cohesive strength C0 and porefluid pressure ratio λ, and decrease with increasing basal friction angle ϕb and basal dip β. Normalized width is sensitive to ϕ and relatively insensitive to ϕb and λ. Results for submarine and subaerial wedges follow the same scaling law. The scaling law relates the observables, w0/H and β, to the material properties, ϕ, ϕb, λ, and therefore provides a theoretical relation that can be used independent of, or together with critical Coulomb wedge theory (CWT) to constrain these properties.
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    Oceanic fault zones reconstructed
    ( 2021-03-18) Garrett Ito
    At undersea structures called oceanic spreading centres, two tectonic plates split apart, and molten rock from volcanic activity solidifies to produce the crust of the sea floor. These spreading centres are separated into individual segments that are tens to hundreds of kilometres long. At the ends of the segments, shearing (side-by-side sliding) of the two plates occurs along plate boundaries known as oceanic transform faults. Since their discovery in the mid-1960s 1, these faults have been considered as sites where plate material is neither created nor destroyed. But on page 402, Grevemeyer et al. 2 report that this description is too simplistic. They show that, in a several-kilometre-wide region called the transform deformation zone, the crust generated at one spreading segment undergoes episodes of thinning and then regrowth as it drifts towards and past the adjacent segment.
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    Honing in on the climate signal in seafloor topography
    ( 2022) Garrett Ito
    The corrugated surface of the seafloor expresses the most areally extensive landform on Earth, known as “abyssal hills”, inherited from when the oceanic crust was created at a midocean ridge spreading center (1, 2) (Fig. 1). The main process is the shifting and rotation of adjacent blocks of crust relative to one another along fault zones predominantly during periods of low magmatic activity, interspersed between times of robust magmatism and the emplacement new crust (1, 3). In the presence of the steady far-field tug of plate tectonic forces, this interplay between faulting and magmatism depends on processes influencing the time dependence of magma generation, storage, and delivery to the surface (4, 5). In PNAS, Huybers et al. (6) argue that one such process originates with the fall and rise of sea level during glacial–interglacial climate cycles.
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    East Pacific Rise 9N: Compiled station, shot, and travel time data for EPR88, EPR93, and EPR97
    ( 2022-01-05) Dunn, Robert
    A combined data set is provided that gives the station and source position information and travel time data for three combined active-source ocean bottom seismograph data sets located along the East Pacific Rise near latitude 9˚N.
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    The Brugd Undergraduate Student Data Solution: A Data Management Collaboration Between Global Environmental Science and Hamilton Library at the University of Hawaiʻi at Mānoa
    ( 2021-08-13) Ramfelt, Oscar ; Guidry, Michael W. ; Young, Jonathan S.
    This paper describes the outcome of the Brugd project, a customized data management solution for undergraduate student learning analytics in the University of Hawaiʻi at Mānoa Global Environmental Science program, with guidance from librarians at Hamilton Library. Our collective effort was to develop a sustainable means of combining past, present, and future institutional and programmatic-collected sources of undergraduate student data, specifically for the Global Environmental Science Program, into a common database for analysis and visualization. The resulting database also needed to be anonymized to both address student privacy concerns and so that resulting analyses could be easily shared and communicated amongst researchers, faculty, and other program stakeholders. This project may serve as a model for in-house learning analytics tools and future data management collaborations between the library and departments both at UHM and other institutions.
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    Extensive Magmatic Heating of the Lithosphere Beneath the Hawaiian Islands Inferred From Salt Lake Crater Mantle Xenoliths
    ( 2020-11-13) Guest, Imani ; Ito, Garrett ; Garcia, Michael O. ; Hellbrand, Eric
    An ongoing challenge in studies of the oceanic upper mantle is how intraplate hotspots impact the thermal structure of the lithosphere. To address this issue at the Hawaiian hotspot, we analyze mineral compositions for a petrographically diverse suite of garnet pyroxenite xenoliths from the Salt Lake Crater (SLC) rejuvenation stage, volcanic tuff ring in Honolulu. Garnet-clinopyroxene geobarometry and two-pyroxene geothermometry indicate equilibrium pressures of 13–18 kbar and temperatures of 1000°C–1100°C. These pressures place the xenoliths at mid-lithospheric depths of 45–55 km, with temperatures 200°C–300°C hotter than expected for normal 90-Myr-old oceanic lithosphere. Garnet and clinopyroxene occur as discrete primary grains, as well as exsolution blebs and lamellae, with lateral dimensions up to several hundred microns. Compositions within garnet and pyroxene grains are remarkably uniform and display no systematic variation with distance to grain boundaries. Together, these observations indicate that the calculated pressures and temperatures reflect the thermal state of the lithosphere under which the xenoliths last equilibrated. We attribute the elevated lithospheric temperatures under Honolulu primarily to the heating by magma as it penetrated the lithosphere during rejuvenation magmatism and the voluminous shield magmatic stage. We anticipate such magmatic heating to be common among all Hawaiian volcanoes, supporting conclusions of a recent study of earthquakes beneath Hawai‘i Island. This local lithospheric thermal anomaly may also contribute to the enigmatically weak flexural response of the lithosphere due to volcano loading along the Hawaiian hotspot chain.
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    Science Commuication Portfolio: A guide to creating communication materials that complement your science
    ( 2015-04-06) Wood-Charlson, Elisha M ; Varga, Melissa
    Are you working on a research manuscript, grant, annual report, or project summary that requires technical language? Do you feel that your finding, if communicated properly, could be useful to people beyond your professional network? This communication-training document for scientists is designed to help you do just that – on your own time and for a variety of verbal and written communication styles. We also provide an example portfolio on the topic of sea level rise for reference.
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    An unexpected disruption of the atmospheric quasi-biennial oscillation
    (Science, 2016-09-23) Osprey, Scott M. ; Butchart, Neal ; Knight, Jeff R. ; Scaife, Adam A. ; Hamilton, Kevin ; Anstey, James A. ; Schenzinger, Verena ; Zhang, Chunxi
    One of the most repeatable phenomena seen in the atmosphere, the quasi-biennial oscillation (QBO) between prevailing eastward and westward wind jets in the equatorial stratosphere (approximately 16 to 50 kilometers altitude), was unexpectedly disrupted in February 2016. An unprecedented westward jet formed within the eastward phase in the lower stratosphere and cannot be accounted for by the standard QBO paradigm based on vertical momentum transport. Instead, the primary cause was waves transporting momentum from the Northern Hemisphere. Seasonal forecasts did not predict the disruption, but analogous QBO disruptions are seen very occasionally in some climate simulations. A return to more typical QBO behavior within the next year is forecast, although the possibility of more frequent occurrences of similar disruptions is projected for a warming climate.
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    Nonlinear climate sensitivity and its implications for future greenhouse warming
    (Science Advances, 2016-11-09) Friedrich, Tobias ; Timmermann, Axel ; Tigchelaar, Michelle ; Timm, Oliver Elison ; Ganopolski, Andrey
    Global mean surface temperatures are rising in response to anthropogenic greenhouse gas emissions. The magnitude of this warming at equilibrium for a given radiative forcing—referred to as specific equilibrium climate sensitivity (S)—is still subject to uncertainties. We estimate global mean temperature variations and S using a 784,000-year-long field reconstruction of sea surface temperatures and a transient paleoclimate model simulation. Our results reveal that S is strongly dependent on the climate background state, with significantly larger values attained during warm phases. Using the Representative Concentration Pathway 8.5 for future greenhouse radiative forcing, we find that the range of paleo-based estimates of Earth’s future warming by 2100 CE overlaps with the upper range of climate simulations conducted as part of the Coupled Model Intercomparison Project Phase 5 (CMIP5). Furthermore, we find that within the 21st century, global mean temperatures will very likely exceed maximum levels reconstructed for the last 784,000 years. On the basis of temperature data from eight glacial cycles, our results provide an independent validation of the magnitude of current CMIP5 warming projections.
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    Magmatic and tectonic extension at the Chile Ridge: Evidence for mantle controls on ridge segmentation
    (American Geophysical Union, 2016-05) Howell, Samuel M. ; Ito, Garrett ; Behn, Mark D. ; Martinez, Fernando ; Olive, Jean-Arthur ; Escartin, Javier
    We use data from an extensive multibeam bathymetry survey of the Chile Ridge to study tectonomagmatic processes at the ridge axis. Specifically, we investigate how abyssal hills evolve from axial faults, how variations in magmatic extension influence morphology and faulting along the spreading axis, and how these variations correlate with ridge segmentation. The bathymetry data are used to estimate the fraction of plate separation accommodated by normal faulting, and the remaining fraction of extension, M, is attributed primarily to magmatic accretion. Results show that M ranges from 0.85 to 0.96, systematically increasing from first-order and second-order ridge segment offsets toward segment centers as the depth of ridge axis shoals relative to the flanking highs of the axial valley. Fault spacing, however, does not correlate with ridge geometry, morphology, or M along the Chile Ridge, which suggests the observed increase in tectonic strain toward segment ends is achieved through increased slip on approximately equally spaced faults. Variations in M along the segments follow variations in petrologic indicators of mantle melt fraction, both showing a preferred length scale of 50620 km that persists even along much longer ridge segments. In comparison, mean M and axial relief fail to show significant correlations with distance offsetting the segments. These two findings suggest a form of magmatic segmentation that is partially decoupled from the geometry of the plate boundary. We hypothesize this magmatic segmentation arises from cells of buoyantly upwelling mantle that influence tectonic segmentation from the mantle, up.