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| Titel |
The 2012 Haida Gwaii earthquake and tsunami: state-of-the-art GNSS ionospheric observations analysis and modeling |
| VerfasserIn |
Lucie Rolland, Anthony Sladen, Carene Larmat, Dylan Mikesell, Virgile Rakoto, Pierre Bosser, Anthony Jamelot, Jean-Xavier Dessa, Jean-Mathieu Nocquet, Philippe Lognonné |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093341
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| Publikation (Nr.) |
 EGU/EGU2014-7973.pdf |
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| Zusammenfassung |
| Large earthquakes (Mw>6) and tsunamis are known to induce ionospheric perturbations
which are frequently observed in the Total Electron Content (TEC) estimated from
multi-frequency Global Navigation Satellite Systems (GNSS) data (e.g., GPS, GLONASS
and soon, Galileo). The Mw 7.8 Haida Gwaii thrust earthquake occurred on 28 October 2012
along the Queen Charlotte fault off the western coast of Canada. This event triggered a
transpacific tsunami having nearly 4 cm height offshore from the Hawaii archipelago. We
report on ionospheric disturbances triggered both in the near-field (< 1000 km) by the sudden
sea-surface uplift at the source (estimated to 2 m) and at further distances by the tsunami
propagation.
The existence of dense regional GNSS networks near the source and in the tsunami
propagation path provides an exceptional data set for state-of-the-art analysis of the coseismic
ionospheric disturbances. We use observations from 22 stations of the Canadian Geological
Survey GPS network. With these data we study the ionosphere directly above the source
region. We also analyzed data from 65 stations in the Hawaiian GNSS network. Because
Hawaii is located along the propagation path of many transpacific tsunamis (e.g. Kurils 2006,
Samoa 2009, Chile 2010, Tohoku 2011 and Haida Gwaii 2012), this is an excellent
location to observe low-frequency (~1.5 mHz) tsunamis-induced ionospheric gravity
waves.
To understand source-related features, we back propagate the near-field ionospheric acoustic
waves to constrain the location of the peak sea-surface uplift. We find the peak is
within 50 km of epicenter locations estimated by other seismological methods.
In addition, we model the GNSS-TEC perturbations in 3 steps: (1) 3D modelling
of the neutral atmosphere perturbations, (2) coupling of the ionosphere with the
neutral atmosphere and (3) integration of the electron density perturbation along each
satellite-station ray path. The neutral atmosphere perturbations in the near field are modelled
using acoustic ray tracing, while in the far field we use atmospheric normal mode
summation.
We observe strong trends in the processed data which are also well reproduced with our
modeling. In the vicinity of the epicenter, strong southward anisotropy of the ionospheric
radiation pattern is observed and is thought to be due to the local geomagnetic effect. We
show that tsunami propagation southward, parallel to the geomagnetic field lines, provides
optimal coupling conditions between the tsunami-induced atmospheric gravity waves and the
ionosphere. Besides the typical Doppler effect due to the GNSS satellites motion,
we illustrate that satellites positioned upstream of the tsunami do not observe the
tsunami-induced ionospheric waves while those positioned downstream do observe the
perturbation. We demonstrate with modeling that this latter observation is related to the 3D
geometrical structure of the tsunami-induced atmospheric gravity wavefront. In the near
future, we anticipate that this kind of data set can be used to constrain the 3D structure of
the tsunami-induced gravity wave, with the ultimate goal of achieving a real-time
estimation of the tsunami amplitude at the ocean level from space geodetic data. |
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