Figure 4

Potential GPS constellation for three IGS (AIRA, MIZU and TSKB) sites located in Japan during the DOY 268 (25 September 2003).

The sites are respectively indicated using gray, red and black lines. We characterize this potential by plotting the number of satellites visible at each site (top panel) and the parameter K (computed every 15 min)at the site 0292 (lower panel) during the day. At the time of the earthquake (vertical red line) the number of satellites available over Japan is close to 10 satellites. Still, we stress that the orientation of these satellites is important too. The parameter K (see text for an accurate description) at the time of the seismic wave propagation is not close (K ∼ 0.2) to the theoretical value of K (∼ 0.93). We indicate the maximal theoretical value with a horizontal red line on the lower panel).