Research ArticleGEOPHYSICS

Areas prone to slow slip events impede earthquake rupture propagation and promote afterslip

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Science Advances  31 Jan 2018:
Vol. 4, no. 1, eaao6596
DOI: 10.1126/sciadv.aao6596
  • Fig. 1 Interseismic coupling map along the central Ecuador subduction zone.

    Yellow stars show the location of the two main aftershocks on 18 May 2016 (Mw 6.7 to 6.9). White lines show the Mw 7.8 16 April 2016 Pedernales earthquake rupture with coseismic slip contours for 1, 3, and 5 m (7). Dashed lines are depth contours of the subduction interface every 10 km. Inset shows the Coulomb failure stress change on the subduction interface computed from the coseismic slip distribution of the 2016 Pedernales earthquake.

  • Fig. 2 Afterslip time evolution.

    (A) Afterslip 30 days following the mainshock. The amount of slip is indicated by the color scale on the left of the figure (in centimeters). Yellow arrows are displacements after the earthquake. Red and green arrows are model-predicted displacements for CGPS sites recorded since the mainshock and installed during the days following the Pedernales earthquake, respectively. Coseismic slip contours (1 and 3 m) of the 2016 Mw 7.8 Pedernales earthquake are in black (7). Dashed gray lines are depth contours of the subduction interface every 10 km. Gray dots show aftershocks (Mw > 3.5) from the IGEPN catalog. (B to G) Snapshots of cumulative afterslip for different time windows.

  • Fig. 3 Slip and seismic moment time evolution for different areas of the plate interface.

    (A to E) Cumulative slip time evolution for the subfault that has the maximum final slip in each area. The curve color is the reduced χ2 for each model according to the color scale shown in (F). Our preferred model is shown by the black curve. The dotted curve in (A) to (C) and (E) shows the cumulative number of earthquakes (Mw > 3) through time, with the scale shown in red on the right edge of each plot. (G to L) Cumulative moment time evolution for the different areas of the plate interface. The scale in red shows Mw. Dashed curves indicate model predictions for alternative models explored in the resolution tests (see the Supplementary Materials).

  • Fig. 4 Summary of slip modes at the plate interface during the earthquake cycle.

    (A) Interseismic phase. Colors indicate interseismic coupling from the studies of Nocquet et al. (7) and Collot et al. (40). Annotations show SSEs (thick blue lines), seismic swarms (light blue dots), and repeating earthquakes (blue squares) before the Pedernales earthquake. SSE areas are defined by the contour line corresponding to 20% of their maximum slip. Light and dashed blue curves are 5 and 2.5 cm isocontours of slip, respectively. (B) Total afterslip as of 30 days after the mainshock contoured every 10 cm (blue lines) and focal mechanisms for primary aftershocks overlain on interseismic coupling (42). (C) Afterslip as in Fig. 2A together with SSEs, seismic swarms, and repeating earthquakes as in (A). (D) Summary of areas that behaved aseismically (A) and seismically (S).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/1/eaao6596/DC1

    Resolution of the inversion and sensitivity tests

    Slip amount required on the northern patch

    Slip amount required on the southern patch

    Slip amount required on the deep patch

    Slip amount required updip of the 2016 earthquake rupture area

    fig. S1. Subduction interface geometry and GPS data used in the study.

    fig. S2. 2D L-curve.

    fig. S3. CGPS east post-earthquake displacement time series (in centimeters).

    fig. S4. Sensitivity test to the CGPS network.

    fig. S5. Resolution test for the northern and southern patches.

    fig. S6. Resolution test for the updip slip and the deep patch.

    fig. S7. Slip evolution and rate-strengthening friction.

    fig. S8. Earthquake swarms in the JCPZ (southern patch of high afterslip).

    fig. S9. Repeating earthquakes in the JCPZ (southern patch of high afterslip).

    fig. S10. Deep SSE.

  • Supplementary Materials

    This PDF file includes:

    • Resolution of the inversion and sensitivity tests
    • Slip amount required on the northern patch
    • Slip amount required on the southern patch
    • Slip amount required on the deep patch
    • Slip amount required updip of the 2016 earthquake rupture area
    • fig. S1. Subduction interface geometry and GPS data used in the study.
    • fig. S2. 2D L-curve.
    • fig. S3. CGPS east post-earthquake displacement time series (in centimeters).
    • fig. S4. Sensitivity test to the CGPS network.
    • fig. S5. Resolution test for the northern and southern patches.
    • fig. S6. Resolution test for the updip slip and the deep patch.
    • fig. S7. Slip evolution and rate-strengthening friction.
    • fig. S8. Earthquake swarms in the JCPZ (southern patch of high afterslip).
    • fig. S9. Repeating earthquakes in the JCPZ (southern patch of high afterslip).
    • fig. S10. Deep SSE.

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