Russian Journal of Earth Sciences
Vol. 6, No. 5, October 2004
Variations of the total electron content in the ionosphere from GPS
data recorded during the
Hector Mine earthquake of October 16, 1999, California
E. L. Afraimovich1, E. I. Astafieva1,
M. B. Gokhberg2, V. M. Lapshin2,
V. E. Permyakova2, G. M. Steblov2,
and S. L. Shalimov2
1 Institute of Solar and Terrestrial Physics (ISTP), Irkutsk, Russia
2 Institute of Physics of the Earth, Russian Academy of Sciences,
Moscow
Abstract
The aim of this paper is to analyze the potential resources of GPS monitoring during
the
recording of potential earthquake precursors using the Hector Mine earthquake that
occurred in California,
USA, in October 16, 1999. This event was chosen because at the time of this fairly
large earthquake
(M=7.1) a dense network of ground-based GPS stations was operating, thus providing
a fairly high spatial
resolution. This paper offers a detailed analysis of the total electron content (TEC)
over a fairly long time
interval including the time of the earthquake (October 13 to 18, 1999).
Examined in this research is the potential manifestation
in the TEC data of the well-known seismo-ionospheric effects: quasiregular changes
in the ionospheric
parameters and internal gravity wave generation. However, our analysis showed that
the observed TEC
variations seem to have been controlled by the local time and by fairly moderate
geomagnetic activity
instead of being associated with any expected processes that usually accompany the
process of earthquake
preparation. Also discussed in this paper are the prospects of detecting small-scale
ionospheric
heterogeneities that are supposed to arise in the course of earthquake preparation,
as follows from our
special measurements of the magnitude and phase flickering of GPS signals.