Research ArticleSeismology

How will induced seismicity in Oklahoma respond to decreased saltwater injection rates?

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Science Advances  30 Nov 2016:
Vol. 2, no. 11, e1601542
DOI: 10.1126/sciadv.1601542
  • Fig. 1 Tectonic and induced earthquakes (M ≥ 3) in Oklahoma (1979 to September 2016).

    The cumulative number of earthquakes is presented in linear (A) and logarithmic scales (B). The map shows the epicenters of the earthquakes in Oklahoma. In 2009, the cumulative number of earthquakes (M ≥ 3) (green line) starts to exceed the constant tectonic earthquake activity (black dashed line). All earthquakes that are inconsistent with a constant tectonic background rate are classified as induced earthquakes (gray shaded area).

  • Fig. 2 Saltwater disposal and earthquakes in Oklahoma.

    The background color shows the cumulative volume (m3) of saltwater injected into the Arbuckle formation between 2009 and December 2015 in different areas of Oklahoma. The saltwater injection volume has been calculated within a radius of 0.5° around a given location on the map and is plotted at the center of the areas (≈8000 km2). Historic earthquakes (1979–2008) are shown as black circles, and recent earthquakes (2009 to September 2016) are presented as gray circles. Areas affected by volume reductions mandated in February and March 2016 are shown as solid (WO) and dashed (CO) lines, respectively. Colored stars show the locations of recent M ≥ 4.5 earthquakes (see main text and table S1).

  • Fig. 3 Combined monthly Arbuckle saltwater injection and induced earthquake rate in CO and WO.

    Monthly Arbuckle saltwater injection (2000 to July 2016) (blue line) and earthquake rate (2009 to September 2016) (green line). Earthquake rate changes follow changes of the injection rate with a time delay of several months. Aftershock sequences are visible in the monthly earthquake rates for the largest magnitudes. The red dashed line shows the normalized pressure rate, which arrives delayed at a depth of 3 km below injection (the average depth of the earthquake hypocenters) (see the Supplementary Materials for more details).

  • Fig. 4 Observation and prediction of induced seismicity in CO and WO.

    Solid colored lines show the combined monthly number of observed earthquakes (green, M ≥ 3; red, M ≥ 3.5) in CO and WO (aftershocks of M ≥ 4.7 events have been removed). The gray dashed lines present the complete earthquake catalog. The colored dotted lines present SI models calibrated through different times between June 2014 and December 2015. Separate figures for CO and WO and the parameter of the SI models are included in the Supplementary Materials (see figs. S4 and S5). The black solid line shows a decay of M ≥ 3 earthquakes according to Omori’s law (see the Supplementary Materials).

  • Fig. 5 Annual magnitude exceedance probability and maximum magnitude in CO and WO.

    The figure shows combined annual probabilities of exceeding magnitude M (A) and the maximum magnitude (B) in the combined area of CO and WO. Magnitude exceedance probabilities have been computed according to Eq. 2 as well as assuming the applicability of Omori’s law to describe the decay of seismicity following injection. The probability of potentially damaging earthquakes is enhanced compared to the tectonic background and critically high in 2014 to 2016.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/11/e1601542/DC1

    Supplementary Methods

    fig. S1. Maximum magnitude expected during 1900 years of tectonic earthquake activity in Oklahoma.

    fig. S2. Saltwater injection and earthquake rate in CO.

    fig. S3. Saltwater injection and earthquake rate in WO.

    fig. S4. Observation and prediction of induced seismicity in CO.

    fig. S5. Observation and prediction of induced seismicity in WO.

    fig. S6. Annual magnitude exceedance probability and maximum magnitude in CO.

    fig. S7. Annual magnitude exceedance probability and maximum magnitude in WO.

    fig. S8. Annual magnitude exceedance probability and maximum magnitude.

    fig. S9. Cumulative magnitude exceedance probability and maximum magnitude in CO and WO (2009 to September 2016).

    table S1. Recent magnitude 4.5 and larger earthquakes in Oklahoma.

    References (28, 29)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Methods
    • fig. S1. Maximum magnitude expected during 1900 years of tectonic earthquake activity in Oklahoma.
    • fig. S2. Saltwater injection and earthquake rate in CO.
    • fig. S3. Saltwater injection and earthquake rate in WO.
    • fig. S4. Observation and prediction of induced seismicity in CO.
    • fig. S5. Observation and prediction of induced seismicity in WO.
    • fig. S6. Annual magnitude exceedance probability and maximum magnitude in CO.
    • fig. S7. Annual magnitude exceedance probability and maximum magnitude in WO.
    • fig. S8. Annual magnitude exceedance probability and maximum magnitude.
    • fig. S9. Cumulative magnitude exceedance probability and maximum magnitude in CO and WO (2009 to September 2016).
    • table S1. Recent magnitude 4.5 and larger earthquakes in Oklahoma.
    • References (28, 29)

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