 
Top of Part 3
Previous p.
Next page
|
On 21 and 22 November 1989,
the earthquake swarm
began beneath Tachibana Bay
(Chijiwa Bay)
at the western foot
of Unzen Volcano
under which the magma chamber
seems to hide itself.
The area of
the hypocenters moved
and broadened with time
towards the east,
and in July, 1990
an earthquake swarm occurred
just under the Mt. Fugen area,
including an earthquake
with the magnitude of M4.9
(the seismic intensity of 3).
Besides, volcanic tremors
were detected,
showing the sign of
movement of lava.
Thereafter, the tremor
continued to occur more frequently.
In addition, there were
observed a damping of
the seismic wave propagating
through the area
just under the summit
of Mt. Fugen.
This seismic activity
in the Shimabara Peninsula
at this time showed a sharp
increase of the underground pressure.
It was seen from
these phenomena that
the underground activity
for eruption of Unzen Volcano
was strengthened at this time,
but we could not predict
the date and time of the eruption.
On 17 November 1990,
the morning edition of
"Kumamoto Nichi-nichi Shinbun"
newspaper
reported
this tense atmosphere
with a headline
"Unzen Volcano, eruption starts?".
The eruption took place
just on this day.
|
