Research ArticleGEOPHYSICS

High mantle seismic P-wave speeds as a signature for gravitational spreading of superplumes

See allHide authors and affiliations

Science Advances  27 May 2020:
Vol. 6, no. 22, eaba7118
DOI: 10.1126/sciadv.aba7118
  • Fig. 1 Bathymetry and topography in the SW Pacific.

    (A) The Ontong-Java (OJP), Manihiki (MP), and Hikurangi (HP) oceanic plateaux are rifted fragments of the once continuous Ontong-Java-Manihiki-Hikurangi Plateau (OJMHP), a LIP that formed over a few million years at about 120 million years (Ma) ago, most likely above a superplume (8). Red arrows show general drift direction of plateau fragments during their breakup; short black bars show seismic profiles analyzed in this study. Parts of the OJP and HP have also been subducted. Inset (B) detailed map of New Zealand region showing SAHKE seismic lines discussed in this study, and earthquake seismic source for SAHKE 04, and ocean bottom seismometers (OBS) 14 and 15, used to determine velocity structure along SAHKE 01 line.

  • Fig. 2 SAHKE showing results for margin normal profile.

    (A and B) P-wave speed models based on ray tracing for SAHKE 04, using earthquake seismic source, and SAHKE 01 derived from gathers for airgun seismic sources for OBS 14 and 15 (fig. S5). The range of Pn speeds (8.6 to 8.9 km/s) is consistent with a variety of methods used on the eastern side of the North island. (C) Fit for earthquake-generated Pn across SAHKE 04 array, indicating best-fit P-wave speeds of 8.7 to 8.9 km/s. Plotted with reduced travel time; reduction velocity of 8 km/s. (D) As for (C) but showing best fit for fast (Vsh) and slow (Vsv) S waves of ~5.1 and ~4.65 km/s, respectively, for upper mantle at depths of >25 km. (E) Reduced seismic data plotted against trace number for SAHKE 04, showing S-wave mantle splitting with well defined (Vsv) and attenuated (Vsh); slower crustal S-wave phases (<4 km/s) indicated. (F to H) Three-component seismometer SAHKE 04 arrays show arrivals of (F) vertical, (G) East horizontal, and (H) North horizontal components for earthquake source (GeoNet earthquake #3511915). The S wave is the slow (blue arrows, ~4.6 km/s) vertical phase, apparent in the vertical component. Upper mantle P-wave arrivals are also shown (green arrows, 8.7 to 8.8 km/s).

  • Fig. 3 Seismic anisotropy in a plume head beneath a LIP.

    (A) Reconstruction of LIP comprising the OJMHP at about 120 Ma ago (8), showing the location of seismic profiles and position above underlying superplume at the time of formation. (B) Schematic depiction of the early stages of superplume growth beneath OJMP, showing mantle flow lines and both radial and azimuthal seismic anisotropy in the plume head. (C) Model of late-stage collapse of superplume head after tail becomes exhausted, showing AG compaction fabric, with radial seismic anisotropy only. See figs. S10 to S12 for full numerical simulations of these properties. (D) Plot showing relation between upper mantle P-wave speed beneath OJMHP and orientation of seismic line (relative to reconstructed north) in which speed was measured, indicating negligible azimuthal anisotropy.

Supplementary Materials

  • Supplementary Materials

    High mantle seismic P-wave speeds as a signature for gravitational spreading of superplumes

    Tim Stern, Simon Lamb, James D. P. Moore, David Okaya, Katharina Hochmuth

    Download Supplement

    The PDF file includes:

    • Supplementary Materials and Methods
    • Figs. S1 to S12
    • Table S1
    • Legend for movie S1

    Other Supplementary Material for this manuscript includes the following:

    Files in this Data Supplement:

Stay Connected to Science Advances

Navigate This Article