Research ArticleGEOPHYSICS

Scattered wave imaging of the oceanic plate in Cascadia

See allHide authors and affiliations

Science Advances  14 Feb 2018:
Vol. 4, no. 2, eaao1908
DOI: 10.1126/sciadv.aao1908
  • Fig. 1 Map of the study region.

    Background colors shows bathymetry/topography. Star indicates Axial Seamount, which is the surface expression of the Cobb Hotspot. Inverted triangles show seismometer locations on the ocean bottom (red) and on land (blue). Thin black lines show the locations of cross sections in Fig. 2. Black circles along the cross sections correspond to a spacing of 100 km. Thick black lines show plate boundaries, and serrated line shows the trench. FZ, fracture zone.

  • Fig. 2 Receiver functions and comparison to predictions from geodynamic models.

    (A to C) Receiver function cross sections as located in Fig. 1. Red phases correspond to velocity increases with depth. Blue phases correspond to velocity decreases with depth. Inverted triangles show the seismometer locations on the ocean bottom (red) and on land (blue) within 0.5° of the transect and plotted at the appropriate bathymetry/topography (Topo) (black line). Black circles at 125 km depth correspond to 100 km spacing along the cross section. JdF Ridge, Juan de Fuca Ridge. (D) Receiver function predictions for the geodynamic model of the Gorda Plate with up to 1% melt volume retention. (E) Receiver function prediction for the geodynamic model of the Gorda Plate with no melt retention. Seafloor age is indicated (24). (F) Geodynamic model. Background color shows the temperature. Contours show retained melt volume fraction.

  • Fig. 3 Map view of receiver function discontinuity depths.

    (A) Shallow negative ocean LAB discontinuity. (B) Positive discontinuity at the base of the melt triangle. Axial Seamount, which is the surface realization of the Cobb Hotspot (yellow star), Juan de Fuca Ridge (JdFR), Gorda Ridge (GR), Blanco Fracture Zone (BFZ), and the Mendocino Fracture Zone (MFZ) are indicated on the map. Thin black lines show the locations of cross sections in Fig. 2. Thick black lines show plate boundaries.

  • Fig. 4 Averaged age-depth relationship of the LAB.

    (A) Colored lines show large (2 My) age bin stacks of S-to-P receiver functions listed at the bin center. Amplitude is normalized to minimize the effects of lateral heterogeneity and emphasize the age-depth trend. (B) Receiver function LAB depths from averages of individual bins in the 3D model (red circles) and from waveform stacks of large age bins over the entire study area (black circles) and over just the Gorda Plate (cyan circles) compared to the predicted receiver functions for the geodynamic model (1350°C) that includes melt retention and upwelling over a broad zone, presented as background shading [red (Moho) and blue (LAB)]. A 1200°C isotherm from a half-space cooling model is also shown (green line). We present Gorda separately because the age bin stacks are dominated by Juan de Fuca.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/2/eaao1908/DC1

    section S1. Sediment property calculation

    section S2. Water column/sediment artifacts

    section S3. Alternate migration models

    section S4. Dipping layers

    section S5. Model reliability

    section S6. Comparison between geodynamic models and receiver functions

    section S7. Additional geodynamic modeling details

    table S1. P-to-S delays measured from Cascadia Initiative Array stations.

    fig. S1. Map view of negative receiver function discontinuity at 60 to 80 km.

    fig. S2. Example of good-quality ocean-bottom seismograms and receiver functions.

    fig. S3. Average delay times at each station between P-wave arrival and P-to-S conversion from the base of the sediment layer.

    fig. S4. Sediment VP and VS used in the waveform rotation and migration derived from P-to-S sediment conversion delay times at each station.

    fig. S5. Comparison of sediment thickness estimate to global sediment thickness (50).

    fig. S6. Example of receiver functions recorded at single stations.

    fig. S7. Example of receiver function and geodynamic models.

    fig. S8. Comparison of geodynamic models and seismic predictions.

    References (4859)

  • Supplementary Materials

    This PDF file includes:

    • section S1. Sediment property calculation
    • section S2. Water column/sediment artifacts
    • section S3. Alternate migration models
    • section S4. Dipping layers
    • section S5. Model reliability
    • section S6. Comparison between geodynamic models and receiver functions
    • section S7. Additional geodynamic modeling details
    • table S1. P-to-S delays measured from Cascadia Initiative Array stations.
    • fig. S1. Map view of negative receiver function discontinuity at 60 to 80 km.
    • fig. S2. Example of good-quality ocean-bottom seismograms and receiver functions.
    • fig. S3. Average delay times at each station between P-wave arrival and P-to-S conversion from the base of the sediment layer.
    • fig. S4. Sediment VP and VS used in the waveform rotation and migration derived from P-to-S sediment conversion delay times at each station.
    • fig. S5. Comparison of sediment thickness estimate to global sediment thickness (50).
    • fig. S6. Example of receiver functions recorded at single stations.
    • fig. S7. Example of receiver function and geodynamic models.
    • fig. S8. Comparison of geodynamic models and seismic predictions.
    • References (48–59)

    Download PDF

    Files in this Data Supplement:

Navigate This Article