[50] Using formulae (8)-(12) in the approximation of the spherical disturbance front for the events on 25 September 2003 and 4 June 2000 the values of the coordinates Fs and Ls, time moment ts, and the delay dt of the ID source switching relative to the moment of the main shock t0, and also of the radial velocity Vr of the ID motion and spatial discrepancy s for various values of the height hs of the assumed ID source were calculated (Tables 1 and 2).
[51] Besides these values, the mean value of the vertical velocity Vv of propagation of acoustic disturbance from the epicenter to the secondary source in the ionosphere was calculated using the simple relation
![]() | (16) |
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Figure 6 |
[53] The coordinates of the ID source calculated with an accuracy of 50-60 km agree well with the position of the earthquake epicenter. The difference between the obtained and true (determined from seismic data) values may be explained by the fact that an approximation of the plain Earth was used in the method. This approximation gives corresponding deviation at a distance of about 500 km.
[54] Moreover, the presence of the meridional and zonal winds at ionospheric heights leads to a shift and deformation of the wave front and, respectively, to appearance of the dependence of the acoustic wave intensity on the propagation direction. Here the deciding role is played by the wind velocity gradient [Ahmadov and Kunitsyn, 2003, 2004; Li et al., 1994]. This can explain the shift of the horizontal position of the secondary disturbance source in the ionosphere relative to the earthquake epicenter.
[55] The phase velocity of the ID motion at the height hd may be more precisely determined in the approximation of the plain front for groups of subionospheric points if the distance between these points satisfies the approximation of the plain wave (Figure 5). In our experiment such approximation is fulfilled for ID generated during the Hokkaido earthquake. For the nearest to the epicenter set of subionospheric points (MIZU, USUD, TSKB; PRN 13) located to the southeast from the epicenter (marked by letter A in Figure 1), the direction a of the propagation wave vector and phase velocity were found 140o and Vh=1093 m s-1, respectively. For the more distant GPS grating (USUD, KGNI, KSMV; PRN 24) located to the southwest from the epicenter (marked by a letter B in Figure 1), the value of the phase velocity Vh=1050 m s-1 almost did not change; however, the direction angle was found equal to a=210 o. In Figure 1 the segments A and B mark fragments of the plain wave front on the circles corresponding to the position of the spherical front of the disturbance at the moments 2000:067 UT and 2003 UT. Adjacent to them the values of the direction and phase velocity of the wave are written.
[56] The value of Vh determined in such a way makes it possible to chose between various values of the height hs of the assumed source of the ID spherical wave presented in Table 3. The value Vr=700 m s-1 for the source at a height of hs=400 km is the closest value of Vh for the 25 September 2003 event. The difference between these velocities may be explained by the fact that the Earth spherical form and different geometry of the rays to the PRN 13 and PRN 24 satellites [Afraimovich et al., 1998] are not taken into account in the used procession method [Afraimovich et al., 2002a].
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