Three-dimensional ionospheric tomography of post-seismic perturbations produced by the Denali earthquake from GPS data

Abstract

SUMMARY The coupling between the solid earth and its atmosphere is responsible for vertically propagating infrasonic waves generated by seismic surface waves. These pressure waves are amplified as they propagate upward, and produce perturbations of ionospheric electron density. The electron density perturbations above California, due to the seismic surface waves generated by the Denali earthquake on 2002 November 3, have been imaged from GPS data by a tomographic method. The integrated electron content along GPS ray paths presents a noise level that is lower in the acoustic wave frequency band than in the gravity wave frequency band. Therefore, the filtered GPS data from Californian networks are inverted for a tomographic reconstruction of electron density perturbations in the acoustic frequency band. The inversion is properly resolved only in a small number of areas due to the geometry of GPS ray paths. In these areas, a wave propagating upward at 1.2 ± 0.3 km s−1 and horizontally at 4 ± 1 km s−1 is observed, with a timing consistent with an infrasonic wave generated by the path of seismic surface waves. The discrepancies between the observed electron density perturbation structure and the expected infrasonic wave can be explained by the poor resolution of the inverse problem or by a simple model of interactions between the neutral wave and the plasma. Future development of dense GPS networks and the advent of the Galileo system will overcome the resolution problems, and allow us to relate ionospheric perturbations to the seismic signal. Such a relation can be used to constrain the source and propagation of seismic waves as well as upper atmosphere characteristics.