Research ArticleEARTHQUAKES

Earthquake forecasting during the complex Amatrice-Norcia seismic sequence

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Science Advances  13 Sep 2017:
Vol. 3, no. 9, e1701239
DOI: 10.1126/sciadv.1701239

Figures

  • Fig. 1 Space-time evolution of the Amatrice-Norcia seismic sequence.

    (A) Seismicity above M3.5 observed during the sequence. Red, seismicity from 24 August to 29 October 2016; light blue, seismicity from 30 October 2016 to 17 January 2017; green, seismicity from 18 January to 31 January 2017. (B) Time evolution of the daily number of earthquakes of M3 or larger in the whole region. (C) Plot of the space-time evolution of the M2.5+ seismicity projected along the axis X-X′ shown in Fig. 1A.

  • Fig. 2 Some examples of weekly forecasts (the number of the forecasts are reported on Table 1).

    (A) Forecast number 3, a few hours after the Amatrice earthquake and the M3.5+ earthquakes (blue-green circles) that occurred in the forecasting time window. (B) Forecast number 15, before the M5.9 earthquake (blue-green star) that occurred on October 26. (C) Forecast number 18, before the Norcia M6.5 earthquake (blue-green star) that occurred on October 30. (D) Forecast number 35, before the Campotosto M5.5 earthquake (blue-green star) that occurred on January 18.

  • Fig. 3 Results of the statistical tests.

    (A) The quantile score ζ for each forecast of Table 1. Dot size is proportional to the number of target earthquakes that occurred during the forecasting time window; the red dashed horizontal line is the critical value (ζ = 0.05) for rejection. (B) Expected number of target earthquakes for each forecast, calculated with negative binomial distribution (NBD) at 99% (see Materials and Methods). The green and red dots represent the following observations: green if inside the expected range and red if otherwise. (C) Probability distribution of the expected number of target earthquakes with a 95% confidence interval (red tails) and the observed number of target earthquakes (vertical dashed blue line). (D) Plot of the forecast and observed frequency-magnitude distribution. The P value of the Lilliefors test is reported inside the plot. These results show that the space-time-magnitude distribution of the forecasts and of the target earthquakes is in agreement.

  • Fig. 4 Weekly exceedance probability for macrointensities VII (gray line) and VIII (black line) for a circular area around Norcia with a radius of 10 km.

    Top: A time period of 3 years including the L’Aquila earthquake (an M6.2 earthquake that occurred in 2009 at about 55 km of distance) (to give an idea about the background values). Bottom: A time period of few months, from 1 August to 29 October 2016, the day before the Norcia earthquake (M6.5). The increase in probability before the Norcia earthquake (bottom right) is caused by the increase in seismicity following the M5.4 earthquake that occurred on 26 October at the north of Norcia.

Tables

  • Table 1 Forecast number (as used in Figs. 2 and 3) and the starting date.

    UTC, Coordinated Universal Time.

    ForecastStarting dateForecastStarting date
    1*24 August 2016,
    0200 UTC
    2130 October 2016,
    1345 UTC
    2*24 August 2016,
    0300 UTC
    2201 November 2016,
    0815 UTC
    324 August 2016,
    1215 UTC
    2303 November 2016,
    0000 UTC
    425 August 2016,
    0000 UTC
    2403 November 2016,
    0100 UTC
    525 August 2016,
    0345 UTC
    2510 November 2016,
    0000 UTC
    626 August 2016,
    0445 UTC
    2617 November 2016,
    0000 UTC
    701 September 2016,
    0000 UTC
    2724 November 2016,
    0000 UTC
    808 September 2016,
    0000 UTC
    2801 December 2016,
    0000 UTC
    915 September 2016,
    0000 UTC
    2908 December 2016,
    0000 UTC
    1022 September 2016,
    0000 UTC
    3015 December 2016,
    0000 UTC
    1129 September 2016,
    0000 UTC
    3122 December 2016,
    0000 UTC
    1206 October 2016,
    0000 UTC
    3229 December 2016,
    0000 UTC
    1313 October 2016,
    0000 UTC
    3305 January 2017,
    0000 UTC
    1420 October 2016,
    0000 UTC
    3412 January 2017,
    0000 UTC
    1526 October 2016,
    1730 UTC
    3518 January 2017,
    0945 UTC
    1626 October 2016,
    1945 UTC
    3618 January 2017,
    1015 UTC
    1726 October 2016,
    2200 UTC
    3718 January 2017,
    1030 UTC
    1827 October 2016,
    0000 UTC
    3818 January 2017,
    1345 UTC
    19*30 October 2016,
    0700 UTC
    3919 January 2017,
    0000 UTC
    2030 October 2016,
    1215 UTC
    4026 January 2017,
    0000 UTC

    *The forecasts that were modified in real time with empirical corrections because of severe seismic catalog underreporting immediately after large earthquakes.

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