10s-period volcanic tremors observed over a wide area in southwestern Japan,
Kawakatsu, H., T. Ohminato, and H. Ito
Geophys. Res. Lett., 21,
1963-66, 1994.
Abstract
Unusual seismic oscillations with a period of 10 seconds
were observed over a wide area of southwestern Japan.
Several lines of evidence indicate that the origin of these 10s
waves must be around the Aso volcano, located in the central part of
Kyushu Island, Japan.
Although a 10s period is unusually long for a volcanic tremor
and no corresponding surface activity at the crater was
reported by the local observatory, the volcanic origin of the tremor
is indisputable.
A further astonishing aspects of the observation is that there exists
a strong correlation between the onset of 10s waves observed remotely and
cessation of high-frequency (>1Hz) volcanic tremors at the Aso volcano.
The Aso volcano appears to be trembling with a 10s period
without this having been noticed.
Since seismic monitoring of volcanic activity is limited to high
frequencies (above 1 Hz) at the most of the volcanoes in the world,
long-period tremors of the type observed here
might be a widespread phenomenon that has been overlooked.