Figure 1. The geometry of the October 13-18, 1999, experiment. The dots show the locations of the GPS sites, the data of which were used in this paper. Due to lack of space the names are given only for some stations. The asterix denotes the epicenter of the earthquake, the crosses denote the locations of the nearest TUCSON and FRESNO magnetic variation sites, the rhomb denoting the Point Aruello ionospheric station.