Limits...
Prompt gravity signal induced by the 2011 Tohoku-Oki earthquake

View Article: PubMed Central - PubMed

ABSTRACT

Transient gravity changes are expected to occur at all distances during an earthquake rupture, even before the arrival of seismic waves. Here we report on the search of such a prompt gravity signal in data recorded by a superconducting gravimeter and broadband seismometers during the 2011 Mw 9.0 Tohoku-Oki earthquake. During the earthquake rupture, a signal exceeding the background noise is observed with a statistical significance higher than 99% and an amplitude of a fraction of μGal, consistent in sign and order of magnitude with theoretical predictions from a first-order model. While prompt gravity signal detection with state-of-the-art gravimeters and seismometers is challenged by background seismic noise, its robust detection with gravity gradiometers under development could open new directions in earthquake seismology, and overcome fundamental limitations of current earthquake early-warning systems imposed by the propagation speed of seismic waves.

No MeSH data available.


Related in: MedlinePlus

Comparison between observations and a theoretical model.(a) Analytical computation of the gravity perturbation produced at Kamioka by the Tohoku-Oki earthquake. (b) The 30 s sliding-averaged theoretical prediction (solid blue) and observed reduced gravity signals (black). (c) Gravity perturbation near the P-wave arrival, with (solid blue) and without (dashed blue) sliding-average, as a function of distance to the earthquake centroid. The duration of the averaging window is increased with increasing distance to the source. The red line is the standard deviation of the sliding-averaged background noise. The vertical dashed line marks the distance of the Kamioka Observatory, the dot indicates the observed value of the reduced gravity signal at Kamioka.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5121411&req=5

f4: Comparison between observations and a theoretical model.(a) Analytical computation of the gravity perturbation produced at Kamioka by the Tohoku-Oki earthquake. (b) The 30 s sliding-averaged theoretical prediction (solid blue) and observed reduced gravity signals (black). (c) Gravity perturbation near the P-wave arrival, with (solid blue) and without (dashed blue) sliding-average, as a function of distance to the earthquake centroid. The duration of the averaging window is increased with increasing distance to the source. The red line is the standard deviation of the sliding-averaged background noise. The vertical dashed line marks the distance of the Kamioka Observatory, the dot indicates the observed value of the reduced gravity signal at Kamioka.

Mentions: Past models of gravity perturbations generated by earthquakes have been mostly restricted to quasi-static gravity changes15. A first-order analytical model of dynamic gravity transients from earthquakes8 is available for a point-shear dislocation in infinite, homogeneous, non-self-gravitating elastic media. Numerical simulations8 indicate that the model stays adequately accurate even after seismic waves have reached the Earth's surface14. This analytical model is used to predict the gravity perturbation from the Tohoku-Oki earthquake at the Kamioka Observatory and at the location of the F-net stations. More complete models14 will be implemented in further studies. Figure 4a shows the analytical perturbation at the Kamioka Observatory, filtered with the anti-alias filter described in the previous section. We then apply the 30 s sliding average to the filtered analytical prediction (Fig. 4b), and obtain  μGal at the Kamioka Observatory. This value is within 50% of the measured value,  μGal, and has the same sign. We therefore conclude that the observation presented here is consistent with the first-order simple analytical model.


Prompt gravity signal induced by the 2011 Tohoku-Oki earthquake
Comparison between observations and a theoretical model.(a) Analytical computation of the gravity perturbation produced at Kamioka by the Tohoku-Oki earthquake. (b) The 30 s sliding-averaged theoretical prediction (solid blue) and observed reduced gravity signals (black). (c) Gravity perturbation near the P-wave arrival, with (solid blue) and without (dashed blue) sliding-average, as a function of distance to the earthquake centroid. The duration of the averaging window is increased with increasing distance to the source. The red line is the standard deviation of the sliding-averaged background noise. The vertical dashed line marks the distance of the Kamioka Observatory, the dot indicates the observed value of the reduced gravity signal at Kamioka.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121411&req=5

f4: Comparison between observations and a theoretical model.(a) Analytical computation of the gravity perturbation produced at Kamioka by the Tohoku-Oki earthquake. (b) The 30 s sliding-averaged theoretical prediction (solid blue) and observed reduced gravity signals (black). (c) Gravity perturbation near the P-wave arrival, with (solid blue) and without (dashed blue) sliding-average, as a function of distance to the earthquake centroid. The duration of the averaging window is increased with increasing distance to the source. The red line is the standard deviation of the sliding-averaged background noise. The vertical dashed line marks the distance of the Kamioka Observatory, the dot indicates the observed value of the reduced gravity signal at Kamioka.
Mentions: Past models of gravity perturbations generated by earthquakes have been mostly restricted to quasi-static gravity changes15. A first-order analytical model of dynamic gravity transients from earthquakes8 is available for a point-shear dislocation in infinite, homogeneous, non-self-gravitating elastic media. Numerical simulations8 indicate that the model stays adequately accurate even after seismic waves have reached the Earth's surface14. This analytical model is used to predict the gravity perturbation from the Tohoku-Oki earthquake at the Kamioka Observatory and at the location of the F-net stations. More complete models14 will be implemented in further studies. Figure 4a shows the analytical perturbation at the Kamioka Observatory, filtered with the anti-alias filter described in the previous section. We then apply the 30 s sliding average to the filtered analytical prediction (Fig. 4b), and obtain  μGal at the Kamioka Observatory. This value is within 50% of the measured value,  μGal, and has the same sign. We therefore conclude that the observation presented here is consistent with the first-order simple analytical model.

View Article: PubMed Central - PubMed

ABSTRACT

Transient gravity changes are expected to occur at all distances during an earthquake rupture, even before the arrival of seismic waves. Here we report on the search of such a prompt gravity signal in data recorded by a superconducting gravimeter and broadband seismometers during the 2011 Mw 9.0 Tohoku-Oki earthquake. During the earthquake rupture, a signal exceeding the background noise is observed with a statistical significance higher than 99% and an amplitude of a fraction of μGal, consistent in sign and order of magnitude with theoretical predictions from a first-order model. While prompt gravity signal detection with state-of-the-art gravimeters and seismometers is challenged by background seismic noise, its robust detection with gravity gradiometers under development could open new directions in earthquake seismology, and overcome fundamental limitations of current earthquake early-warning systems imposed by the propagation speed of seismic waves.

No MeSH data available.


Related in: MedlinePlus