GPS Remote sensing of seismic waves in the Ionosphere: interpretation and modeling with realistic seismic sources and Solid Earth/atmospheric/ionospheric models. (Invited)

Details GPS Remote sensing of seismic waves in the Ionosphere: interpretation and modeling with realistic seismic sources and Solid Earth/atmospheric/ionospheric models. (Invited) GPS Remote sensing of seismic waves in the Ionosphere: interpretation and modeling with realistic seismic sources and Solid Earth/atmospheric/ionospheric models. (Invited)

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsa51e..01l&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SA51E-01

Statistics

Computation

[2427] Ionosphere / Ionosphere/Atmosphere Interactions, [2487] Ionosphere / Wave Propagation, [7290] Seismology / Computational Seismology, [9810] General Or Miscellaneous / New Fields

Scientific paper

With the development of dense GPS networks, observations of seismic waves in the ionosphere are now common and reported almost systematically after quakes with magnitude larger than 7.5. They are associated to integrated perturbations in the ionospheric electron density at altitude between 250 and 350 km, in contrary to Doppler observations, related to the vertical electrons velocities at altitudes between 150 and 200 km. The observed waves are either acoustic waves, generated by the vertical displacement of the Earth surface near the epicenter and propagating over regional distances (up to about one thousand km) in the atmosphere or acoustic-Rayleigh waves generated by the Rayleigh surface wave front at tele-seismic distance of several thousands km. These waves are observed above the atmospheric cutoff, in contrary to tsunami-induced gravity waves, observed also in the ionosphere but below the Brunt-Väisälä frequency. The modeling of these waves requests not only the modeling of the solid-earth/atmosphere coupling problems but also the one of the atmosphere/ionosphere coupling. It is then mandatory to consider the variability in space and time of the atmosphere and ionosphere (e.g. density, temperature, ions and electron density), as well as magnetic field, in order to model the observed electronic content perturbations. This variability is illustrated by the computation of normal modes of the coupled earth/atmosphere/ionosphere system. This allows us to show the variability of these normal modes in term of eigen-frequencies, atmospheric velocity amplitudes and ionospheric electron perturbation with respect to different conditions in latitude, longitude, local time, month and F10.7 indice. We then present several observations (including after the 5/12/2008 Wenchuan, 12/26/2004 Sumatra-Andaman and 9/25/2003 Tokachi-Oki earthquakes). These observations show clearly the two different types of waves described above, as well as their sensitivity to the observation conditions, especially in term of inclination of the sounding path between the ground receivers and GPS satellites. The observed noise is discussed, including aliasing and multi-pathing effects. These observations are then modeled and the misfit between observed and modeled waveforms are discussed. We especially analyze the crustal, atmospheric and ionospheric effects, as well as the limitation in the models and modeling (e.g. non linearity, heat diffusion and ion-neutral interactions in the atmospheric wave modeling). A special focus is finally given to the modeling of the source, as the later is either smaller than the radiated waves for Rayleigh waves and much larger for the acoustic waves, due to the differences in the propagation speeds (3.5 km/s versus 0.33 km/s). Perspectives are finally given, both in term of future modeling effort or in term of observation efforts, either with better GPS observing systems based on phase array antenna, or with possible space remote sensing techniques.

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