Geoscience Reference
In-Depth Information
In this section we shall not present the entire list of events, but dwell upon the first
case, that was revealed already 10 years ago, and on the results of one of the most
recent works in this direction.
The formation of cold SST anomalies, resulting from a series of strong underwa-
ter earthquakes, was first observed in 1996 near Bougainville Island (Solomon Is-
lands). The phenomenon was revealed by a joint analysis of the maps of SST anoma-
lies (FNMOC, United States Fleet Numerical Meteorology and Oceanography Cen-
tre, http://www.fnmoc.navy.mil/) and of the operative issue of the NEIC seismolog-
ical bulletin (National Earthquake Information Centre, http://earthquake.usgs.gov/).
In the region of Bougainville (within a radius of 300 km from the epicen-
tre of the earthquake of maximum magnitude 6.52S, 155.00E) during the period
from 20.04.1996 to 31.05.1996 there were 145 earthquakes, that were mainly shal-
low. Preceded by several foreshocks, the main earthquake of magnitude 7.5 occurred
on April 29 at 14 h 40 min Greenwich time. The location of the epicentres is shown
in Fig. 7.1.
In Fig. 7.2, the blue line, marked by squares, presents the SST dependence on
time at the point with coordinates 7S, 156E (the centre of temperature anomalies).
The time dependence is reconstructed from maps of SST anomalies (FNMOC) at
our disposal. Analysis of the global ocean surface temperature distribution is per-
formed twice a day (at 00 and 12 GMT), but, regretfully, not all the data turned out
to be available. The presence of a marker (square) signifies the existence of data. As
an example, six fragments of anomaly maps are shown in the figure. The time and
amplitude of seismic events are indicated by red triangles.
The dark-blue spot, the appearance of which in the vicinity of Bougainville Island
is especially well seen on the third and fourth fragments (May 6 and 12), represents
a cold SST anomaly. The maximum deviation of temperature amounts to
3
◦
C
∼
2
◦
C in the second. The characteristic horizontal size of
the anomaly is 300-500 km. Note, that manifestation of the anomaly after the main
shock (second fragment) is just noticeable, and only after a whole series of seis-
mic events, from April 25 to May 5, the anomaly becomes extremely pronounced.
in the first case and to
∼
Fig. 7.1 Earthquake epi-
centres in the vicinity of
Bougainville Island for the pe-
riod April 20 to May 31, 1996.
The centre of the red circle of
radius 300 km is at the point
6.528 S, 155.00 E (epicentre
of earthquake of maximum
amplitude). The black cir-
cles indicate the location of
TAO Array stations (see also
Plate 16 in the Colour Plate
Section on page 324)
0N154E
0N156E
0N158E
2S156E
5S156E
