Research ArticleEARTH SCIENCES

The discovery of a conjugate system of faults in the Wharton Basin intraplate deformation zone

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Science Advances  04 Jan 2017:
Vol. 3, no. 1, e1601689
DOI: 10.1126/sciadv.1601689
  • Fig. 1 The 2012 earthquake rupture zone in the Wharton Basin.

    The blue beach balls represent the 2012 earthquakes, and the brown circles represent the aftershocks. The green beach balls represent strike-slip earthquakes, the black beach balls represent thrust earthquakes, and the red beach balls represent normal faulting earthquakes. “1” and “2” represent two-point W-phase centroid moment tensor (CMT) solutions (18). NER, Ninety East Ridge. The white dashed lines indicate fracture zones F2 to F8. The red, yellow, and black lines indicate different fault models (1416). The black arrow indicates the subduction direction. The green and purple arrows indicate the directions and the relative magnitudes of the principal deviatoric compression and tension components from Gordon and Houseman (7). The light pink area indicates the new bathymetry shown in Fig. 2A. The red rectangle in the inset at the right-hand upper corner shows the main study area.

  • Fig. 2 New bathymetry.

    (A) Uninterpreted bathymetry. Black lines represent seismic profiles acquired. The white line shows the position of the seismic image shown in Fig. 4, and the red lines show the position of the seismic image shown in Fig. 5. (B) Interpreted bathymetry. F6a and F7b, reactivated fracture zones. Different symbols are defined in the right-hand upper corner. NEIC, National Earthquake Information Center; ISC, International Seismological Centre. (C) Simplified interpreted bathymetry showing main features. The inset shows a schematic shear zone scheme.

  • Fig. 3 Rose diagrams.

    The rose diagrams for the average strike of the reactivated fracture zones F6a, F6b, and F7 (A); the shear zones (B); and normal faults bounding the shear zones (blue) (C). Black lines indicate the two conjugate strike-slip faults. σ1 (red) is the principal compressional stress, and σ3 is the principal extensional stress. The light blue marks the principal compressional stress direction determined by one of the previous studies (13).

  • Fig. 4 Interpreted seismic reflection image across reactivated fracture zones.

    Seismic reflection along profile WB03 crossing through four reactivated fracture zones (F6a, F6b, F7a, and F7b). Prominent sedimentary horizons are marked in green. The yellow line marks the top of the pelagic sediments. The red curve marks the top of oceanic basement. Thick black lines, major faults; thin black lines, minor faults. Dashed thin black lines link faults imaged in the sediments with deep-rooted strike-slip faults.

  • Fig. 5 Seismic reflection images of shear zones.

    (A) Interpreted seismic image across a shear zone along the north-south profile WB08. (B) Interpreted seismic image across a shear zone along the east-west profile WB02. Green lines represent sedimentary strata, black lines represent faults, and very thick lines represent deep faults.

  • Fig. 6 The vertical cumulative offset on F6b.

    Interpreted seismic image across F6b along profile WB03 (left) and the cumulative offset as a function of depth across two branches of F6b (F6b1 and F6b2) and as a function of age up to 40 My. F6b1 and F6b2 are two branches of reactivated fracture zone F6b (right). Horizontal color lines indicate horizons used in the right panel. The thin black lines indicate interpreted faults in the sediments, and the thick solid black line indicates the possible position of reactivated fracture zone at depth.

  • Fig. 7 En echelon faulting and the deformation in the Wharton Basin.

    Schematic diagram showing the en echelon rupture during the 2012 Mw 8.6 earthquake. The black solid lines indicate the reactivated fracture zones in an en echelon form (F6a, F6b, F7a, and F7b) along fracture zones (F6 and F7 in yellow). The blue lines indicate en echelon rupture along the shear zones. The Mw 8.2 ruptured fracture zone F7b is marked in orange. The light purple area is shown in Fig. 2. The long black arrows and numbers indicate the direction of subduction and approximate convergence rates (29). The long red arrows indicate the direction of the principal compressional stress determined from our study. The dashed black and blue lines indicate average strike direction of faults during the 2012 Mw 8.6 rupture. Thin dashed gray lines indicate faults F2 and F3 from Wei et al. (16). The inset shows the conjugate faulting along the reactivated fracture zones (black) and shear zones (blue) and the direction of principal compressional (σ1) (red arrow) and extensional (σ3) (green) stresses.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/1/e1601689/DC1

    fig. S1. Different models of the 2012 Mw 8.6 earthquake.

    fig. S2. Seismic reflection images of F6a.

    fig. S3. Seismic reflection images of F6b.

    fig. S4. Seismic reflection images of F7b.

    fig. S5. Bathymetry in the outer rise region.

    fig. S6. Fault offset with age.

    fig. S7. Blow-up seismic image of shear zone.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Different models of the 2012 Mw 8.6 earthquake.
    • fig. S2. Seismic reflection images of F6a.
    • fig. S3. Seismic reflection images of F6b.
    • fig. S4. Seismic reflection images of F7b.
    • fig. S5. Bathymetry in the outer rise region.
    • fig. S6. Fault offset with age.
    • fig. S7. Blow-up seismic image of shear zone.

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