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Observations and modeling of the elastogravity signals preceding direct seismic waves

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Science  01 Dec 2017:
Vol. 358, Issue 6367, pp. 1164-1168
DOI: 10.1126/science.aao0746
  • Fig. 1 Observations of the pre-P signals on broadband seismometers.

    (A) Map of the selected stations located in the 400- to 3000-km hypocentral distance range. The red star shows the Tohoku earthquake epicenter. (B) Acceleration signals Embedded Image in the 0.002 to 0.03 Hz frequency range, represented in a time window starting 30 min before the earthquake origin time and terminating at the P-wave arrival time at each station (1 nm/s2 scale is shown to the right). Names of the stations and their hypocentral distances in kilometers (following Earth’s surface) are shown to the left of each signal. In the time window between origin time and P-wave arrival time, signals are drawn with a thick red curve. ULN, Ulaanbaatar, Mongolia; XAN, Xi’an, China; MA2, Magadan, Russia; BJT, Baijiatuan, China; NE93, Zhalaiteqi Badaerhuzhen, China; INCN, Incheon, Korea; FUK, Fukue, Japan; MDJ, Mudanjiang, China; SHR, Shari, Japan; INU, Inuyama, Japan; MAJO, Matsushiro, Japan.

  • Fig. 2 Reconstruction of the observed elastogravity signals from the effects of the gravity variation and its induced acceleration.

    Examples at close distances [INU (GEOSCOPE) station in Japan] and at optimal distances in terms of signal observability [MDJ (IRIS) station in northeast China] are shown. The induced acceleration Embedded Image cancels the gravity variation Embedded Image at early times and can dominate (INU) or only affect (MDJ) Embedded Image when approaching the P-wave arrival time.

  • Fig. 3 Agreement between observed and modeled Embedded Image signals and influence of the earthquake magnitude.

    Red (observed) and black (simulated) curves are in good agreement at all distances and azimuths from the Tohoku earthquake. The simulation for a fictitious Mw = 8.5 earthquake (dashed blue curve) shows large amplitude differences, directly illustrating the magnitude determination potential existing in these prompt elastogravity signals.

Supplementary Materials

  • Observations and modeling of the elastogravity signals preceding direct seismic waves

    Martin Vallée, Jean Paul Ampuero, Kévin Juhel, Pascal Bernard, Jean-Paul Montagner, Matteo Barsuglia

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Figs. S1 to S4
    • References

    Additional Data

    Data S1
    A procedure to reproduce the prompt elasto-gravity signals (shown in Figure 1), starting from the raw broadband signals.

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