Research ArticleGEOPHYSICS

Daily measurement of slow slip from low-frequency earthquakes is consistent with ordinary earthquake scaling

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Science Advances  02 Oct 2019:
Vol. 5, no. 10, eaaw9386
DOI: 10.1126/sciadv.aaw9386
  • Fig. 1 LFE amplitudes track slow slip in both time and space in Guerrero, Mexico.

    (A) Median S-wave LFE displacement amplitude in 7-week time bins and 15-km spatial bins, normalized by the mean of all plotted median amplitudes; color scale is logarithmic. (B) North-south surface displacement observed at the MEZC GPS station during the 2.5-year LFE record. Colored patches mark geodetically observed slow slip events: the 2006 M7.5 slow slip events [red; (7)] and the M6.4 slow slip events [yellow; (8)]. The dark red patches indicate the intermittent slow transients during the 2006 slow slip event (12), highlighting the short slip duration compared to the 6-month event duration. (C) Schematic of the Guerrero subduction zone, with inset showing geographical location. The two LFE source regions are indicated by the blue and purple boxes. The red and orange patches correspond to areas where geodetically observed slow slip occurs.

  • Fig. 2 Geodetic slow slip moment rate, estimated from GPS surface displacements, scales with the seismic moment rate of slow slip, measured from the displacement amplitudes of LFEs.

    Units of δT reflect the average duration of the aseismic pulses that drive LFE activity; we assume δT = 0.5 s (14, 15) for the right y axis. The squares indicate the moment rates of geodetically observed slow slip events. The blue circles reflect 1-day slow transients, representing the average moment rate for a given range of LFE amplitudes (fig. S1). See Materials and Methods for a discussion of error bars.

  • Fig. 3 Daily tectonic release of slow slip along the Guerrero subduction interface, as tracked by LFEs.

    The yellow and red patches respectively highlight the geodetically observed small M6.4 and large M7.5 slow slip events (Fig. 1). The dark red patches indicate the intermittent slow transients during the 2006 slow slip event (12). (A) Waiting times between successive LFEs in the updip LFE source region highlight the clustered seismicity that accompanies slow slip (29). (B) Evolution of daily slow transient magnitudes, estimated with the moment rate scaling shown in Fig. 2. The small slow slip events are made up of a single group of slow transients, while the 2006 M7.5 slow slip event is composed of a complex cluster of these transients.

  • Fig. 4 Moment scaling of slow transients in Guerrero as inferred from LFEs.

    (A) Slow transient moment Mo scales with the slip duration T3 (blue line), where duration is the number of LFEs multiplied by the average aseismic pulse duration of δT; we assume δT = 0.5 s (14, 15) for the right y axis. The moment-duration scaling is the same as for ordinary earthquakes. (B) Slow transient moment scales with the inter-event interval τ to the power of 5.5 (blue line). The moment–inter-event interval scaling is approximately the same as for repeating earthquakes (orange line).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/10/eaaw9386/DC1

    Fig. S1. Distribution and evolution of LFE displacement amplitudes in Guerrero.

    Fig. S2. Tectonic context of the subduction zone underneath Guerrero, Mexico.

    Fig. S3. Alternative number of slow transients to constrain the seismic to geodetic moment rate relationship shown in Fig. 2.

    Fig. S4. Distribution of slow transient magnitudes.

    Fig. S5. Daily count of the 5% largest LFEs (2337 events); the plotted amplitudes are >12.4 nm.

    Reference (30)

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Distribution and evolution of LFE displacement amplitudes in Guerrero.
    • Fig. S2. Tectonic context of the subduction zone underneath Guerrero, Mexico.
    • Fig. S3. Alternative number of slow transients to constrain the seismic to geodetic moment rate relationship shown in Fig. 2.
    • Fig. S4. Distribution of slow transient magnitudes.
    • Fig. S5. Daily count of the 5% largest LFEs (2337 events); the plotted amplitudes are >12.4 nm.
    • Reference (30)

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