Research ArticleGEOPHYSICS

Revealing the cluster of slow transients behind a large slow slip event

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Science Advances  30 May 2018:
Vol. 4, no. 5, eaat0661
DOI: 10.1126/sciadv.aat0661
  • Fig. 1 Breaking down a large SSE into its constituent slow transients.

    (A) Tectonic context of the subduction zone underneath Guerrero, Mexico. A large SSE in 2006 recorded by GPS (green triangles) accumulated more than 10 cm of slip (thick dashed contour) updip of LFE sources (black points, transient zone; gray points, sweet spot) (22). Depth contours of the subduction interface (50) are shown as thin dashed lines. (B) GPS displacement time series during 2006. The blue patches indicate the set of slow transients that exhibit tectonic release. (C) Daily LFE amplitude sums during the 2006 SSE. We identify slow transients on the days that the daily amplitude sum exceeds the established threshold (dashed black line). The insert shows the distribution of their durations. (D) Cumulative displacements at MEZC during the 2006 SSE before and after decomposition via the LFE amplitude sum in (C). The black trace represents the displacements during the 185-day slow slip duration (16) in (B), while the gray trace shows the inter-SSE displacements during the 185 days before the 2006 event. The red and blue traces respectively show the decomposed loading and release displacements (see main text). The shaded regions represent the estimated motion ±2σ during the slow slip duration of 185 days, of which there are no data at MEZC for 35 days. The slow slip–induced surface displacement of the cluster of slow transients during the release period of the 2006 SSE (blue arrow) is 40% larger than the surface displacement estimated from the GPS time series during the full slow slip duration (black arrow).

  • Fig. 2 Estimating surface displacement rates via LFE amplitudes on the subduction interface.

    Surface displacement rates are computed at each GPS station as a function of increasing daily LFE amplitude sums. Southward surface motion in the direction of tectonic release, which is proportional to the motion on the decoupled interface at depth, becomes pronounced at LFE amplitudes greater than the established threshold (dashed line).

  • Fig. 3 Slow slip as a cluster of slow transients.

    The autocorrelation of the slow slip activity time series in blue (see main text) indicates a temporally clustered distribution of slow transients with a falloff of 185 days (dashed lines), the duration of the 2006 SSE (16). The inter-SSE time period before the 2006 SSE (black) exhibits a Dirac at zero lag, indicative of a random occurrence of slow transients.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/5/eaat0661/DC1

    fig. S1. Decomposition of surface displacement increments into loading and release in Guerrero, Mexico.

    fig. S2. Comparing observed network sum of release displacement (dashed blue line) to a random shuffling of the daily LFE amplitude sum time series.

    fig. S3. Determining the LFE amplitude sum threshold.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Decomposition of surface displacement increments into loading and release in Guerrero, Mexico.
    • fig. S2. Comparing observed network sum of release displacement (dashed blue line) to a random shuffling of the daily LFE amplitude sum time series.
    • fig. S3. Determining the LFE amplitude sum threshold.

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