Geochemistry, Geophysics, Geosystems

Cover image for Vol. 15 Issue 5

Impact Factor: 2.939

ISI Journal Citation Reports © Ranking: 2012: 16/76 (Geochemistry & Geophysics)

Online ISSN: 1525-2027

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  • Nankai trough seismic lines

    Nankai trough seismic lines

    Observed seismic records from the eastern profile and their comparison with synthetic seismograms (modified from Arai et al. []). (a) Observed seismograms of SP1 to which a 1–15 Hz band-pass filter is applied. Each trace is normalized by its maximum amplitude. A red arrow highlights reflected waves from the top of the slab. (b) Synthetic seismograms for SP1 calculated from the velocity model without a low-velocity layer (plot c). We used the amplitude of refractions (first arrivals) and reflections from the subduction interface to match the calculated and observed records. (c) Ray diagrams for SP1 (white lines) plotted on the preferred velocity model used in the analysis. Red lines indicate structural boundaries inferred from wide-angle reflections. (d) Observed seismograms of SP12 to which a 1–15 Hz band-pass filter is applied. A red arrow highlights reflected waves from the top of the slab. (e) Synthetic seismograms for SP12 calculated from the velocity model without a low-velocity layer (plot f). (f) Ray diagrams for SP12 (white lines) plotted on the preferred velocity model used in the analysis, same as in plot c. (g) Migrated depth section by reflection analysis for the eastern profile [Sato et al., ]. Red/black arrows highlight a reflector corresponding to the plate boundary. KB denotes Kanto basin.

  • Subduction dynamics regime diagram

    Subduction dynamics regime diagram

    (left) Regime diagram for subduction dynamics as a function of initial subducting and overriding plate ages, with the modes underlined in Figure for a viscosity jump Δμ of 30 between upper and lower mantle. More discussion on the discrimination between the different modes is made in section . Gray symbols indicate a slab morphology intermediate between two subduction modes. Increasing Δμ yields more HD cases, as explained in section . (right) Slab morphologies at t660 (black contour) and at t800 (gray fill). Black squares indicate initial trench location, length scales correspond to 200 km, and the dashed line indicates the 660 km viscosity jump.

  • Seismic anisotropy of the Slave craton as determined from SKS-splitting techniques

    Seismic anisotropy of the Slave craton as determined from SKS-splitting techniques

    Seismic anisotropy of the Slave craton as determined from SKS-splitting techniques [Snyder and Bruneton, ]. Vertical red shingles indicate fast polarization direction (strike) and modeled splitting delay time (size of panel) within three depth layers and compared to seismic discontinuities discussed previously. Vertical columns are rock “cores” as determined from xenolith suites [Kopylova and Caro, ]. Cones are representative multiazimuthal receiver functions at stations GALN and GDLN. Gray balls at top mark all seismic station locations. (a) View here is from the side at about 180 km depth, looking toward the northeast (approximately 050°), along strike with the deepest layer anisotropy. (b) View from below allows comparison of fast polarizations with Lac de Gras discontinuity (blue surface) and surface geology. (c) View from below shows deepest layer SKS anisotropy markers against the bottom of the midlithospheric discontinuity (gold surface); objects as in Figure a. Note change in fast polarization across dashed line, dividing the central and southern Slave craton.

  • Acoustic anomalies in the water and sediment columns

     Acoustic anomalies in the water and sediment columns

    Acoustic anomalies in the water and sediment columns. (a) An echogram of the 2012 survey (38 kHz) at the Vestnesa Ridge shows examples of flares (black arrows). The volume backscattering strength of the received sound signal (Sv) is given by the color of the bubble plumes. The flares show a deflection toward the North due to the bottom-water current (8 cm s−1) [Fahrbach et al., ] in the eastern Fram Strait. (b) Example of a seismic reflection profile through pockmarks from a 2010 3-D P-Cable Survey [Bünz et al., ] with two-way traveltime (TWT) on the vertical axis. Enhanced reflections (green circles) and “push-down” features (black circles) are present within the HSZ. We interpret these features to record the presence of free gas. Acoustically transparent zones, interpreted as gas chimneys, extend from the seafloor to depths below the BSR. These gas-rich vertical intrusions create significant lateral variations in the BHSZ (inset). The location of flares coincides with areas where chimneys are visible in the seismic data; however, there are several gas chimneys above which no flares are present. Location of echogram and reflection profile is shown in Figures and .

  • Zero-field micromagnetic domain structures for grain size of 80 nm with oxidation parameter z

    Zero-field micromagnetic domain structures for grain size of 80 nm with oxidation parameter z

    Zero-field micromagnetic domain structures for grain size of 80 nm with oxidation parameter, z, equal to (a) 0, (b) 0.271, (c) 0.488, (d) 0.784, (e) 0.992, and (f) 1. For each model, the sample's magnetizations was saturated along the [111] direction. All structures share the same color coding of magnetization as Figure . Translucent isosurfaces have been drawn for illustrative purposes. They are surfaces containing all moments lying within 20° of the [111] direction in Figures a–c, and f and 10° in Figures d and e, respectively.

  • Cross-wavelet transform (XWT) and wavelet transform coherence (WTC) of 3He/4He and axial depth

    Cross-wavelet transform (XWT) and wavelet transform coherence (WTC) of 3He/4He and axial depth

    (a) Cross-wavelet transform (XWT) and (b) Wavelet transform coherence (WTC) of 3He/4He and axial depth. The vertical axis is a natural logarithm scale of the length scale (km) with each unit corresponding to a doubling in size. Signal power (a) and coherence (b) are contoured in color according to the scale shown at the right. Arrows depict the phase relationship between 3He/4He and axial depth as a function of length scale (vertical axis) and location along the SEIR (horizontal axis). Right-pointing arrows indicate an in-phase relationship and left-pointing an antiphase relationship. Downward pointing arrows correspond to where axial depth leads 3He/4He, while upward pointing corresponds to where depth lags. Thick contours outline 5% significance levels.

  • Estimated interseismic coupling (phi) along the Nicoya and Osa segments of the MAT as predicted by the best fit model with no coupling constraints

    Estimated interseismic coupling (phi) along the Nicoya and Osa segments of the MAT as predicted by the best fit model with no coupling constraints

    (a) Estimated interseismic coupling (phi) along the Nicoya and Osa segments of the MAT as predicted by the best fit model with no coupling constraints. Open arrows show velocity of the Cocos plate relative to the overriding CAFA and PB blocks. Gray, white, and pink dots indicate epicenters of historical earthquakes along the Nicoya and Osa segments of the MAT and western NPDB [Abe, ; Adamek et al., ; Protti et al., ; Pacheco and Sykes, ; National Earthquake Information Center, ]. Dashed loops, rupture area for selected events. Color of dashed loops is the same as the corresponding epicenter. Inset: Estimated slip deficit on the (b) Nicoya and (c) Osa segments of the MAT.

  • Nankai trough seismic lines
  • Subduction dynamics regime diagram
  • Seismic anisotropy of the Slave craton as determined from SKS-splitting techniques
  •  Acoustic anomalies in the water and sediment columns
  • Zero-field micromagnetic domain structures for grain size of 80 nm with oxidation parameter z
  • Cross-wavelet transform (XWT) and wavelet transform coherence (WTC) of 3He/4He and axial depth
  • Estimated interseismic coupling (phi) along the Nicoya and Osa segments of the MAT as predicted by the best fit model with no coupling constraints

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