Geoscience Reference
In-Depth Information
In a geophysical sense, New Zealand sits in a precarious position because it gets
astride the boundary between the Pacifi c and Australian Plates. There are other two
potential sources of large seismic activity: the Tonga-Kermadec trench and the New
Hebrides one. The Tonga trench extends from the southern periphery of the Samoa
Islands up to the connection with the Kermadec trench. The Kermadec trench connects
the Tonga Trench to the north with the Northern Island of New Zealand to the south.
The Kermadec and the Tonga trenches can be considered as one representative struc-
tural unit of Tonga-Kermadec Trench (Goff et al., 2006; Walters et al., 2006). The
pass of INTERCOSMOS-BULGARIA1300 for orbits 170, 213, and 527 is shown in
Figure 2a. The earthquake epicenters take place in a relatively long and wide area. The
analysis of the Figure 2b indicates that the ionospheric anomalous disturbance zone
follows the same wide latitudinal interval of earthquake epicenters. The fi rst changes
in
E
z
component of the quasi-statistic electric fi eld of about 3 mV/m are due to the cu-
mulative seismic effect 11-42 hr after EQ
3
and EQ
7
. The second changes, showing an
increase in
E
z
component about 2 mV/m, we observe at the beginning of the big bulge.
The established increase could be interpreted like post-seismic effects of EQ
2
(44 hr
after the earthquake). We observe a wide latitudinal interval with big changes and an
increase in
E
z
component about 10-12-18 mV/m. In our opinion, the amplitudes of
this unusually disturbance zone are formed by the cumulative just-post seismic effects
(7 hr) of EQ
9
and forthcoming ones (EQ
18
, EQ
41
, and its foreshock EQ
40
). Summariz-
ing, the indicated big increase of about 18 mV/m might be connected with the major
earthquake EQ
41
with magnitude M
w
7.9 which was happened 13 days later. Any dis-
turbances from EQ
15
and EQ
8
,
13,20
(with hypocenters on the depths 164-507 km and
magnitudes M 4.8; 4.8; 4.9; 4.8) are not noted. In these cases the energetic levels are
very low. The mentioned observations take place in a quiet day K
p
= 3.
Figure 2a.
Satellite orbits 170, 213, 527, and positions of the earth-quake epicenters for period of
seismic activity in August 17-September 17, 1981.
