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.

A generalization of Capon's maximum-likelihood technique for detection and estimation of seismic signals is introduced. By using a multi-dimensional autoregressive approximation of seismic array noise, we have developed a technique to use Capon's multi-channel filter for on-line processing. Such autoregressive adaptation to the curent noise matrix power spectrum is shown to yield good suppression of mutually correlated array noise processes. As an example, this technique is applied to detection of a small Semipalatinsk underground explosion recorded at the ARCESS array.

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