Matsushiro Seismological Observatory, JMA
Yuzo Ishikawa
The Matsushiro Seismological Observatory (MSO) was established on May 1, 1947,
taking advantage of an extensive but unfinished tunnel system built by the military
for wartime needs. The tunnels, about 3km long in total and 2.5 to 6m in diameter,
are ideal for the earthquake observation. Because of their depth, some 100 m below
the hilltop, the temperature of the air in the tunnels changes little through the year.
Being located more than 60 km in land from the nearest Japan Sea coast, the site is
free from the disturbance by sea waves and from the noise of railroads and automobile
traffic.
The MSO gradually expanded its facilities, which include a Benioff seismograph
installed when the MSO participated in the IGY, a World Wide Standardized Seismograph
(WWSS), an
Abbreviated Seismic Research Observatory system (ASRO), a System from the Incorporated
Research Institutions for Seismology (IRIS), and a 100-meter-long two-component quartz-tube
extensometer.
Matsushiro Seismic Array System
The Matsushiro Seismic Array System (MSAS) consists of nine stations with identical
seismometers, seven of them forming a near circle about 10km in diameter and two located
near the circle's center. Signals from these stations are telemetered at the MSO main
office serving as one of the array stations．
This system features：
（1）An S/N ratio superior to that of an individual conventional seismometer．
Centralized computer processing of signals from seismometers having identical
instrumental characteristics eliminates background noise．
（2）The capability to determine seismic parameters without referring to data from
other seismological stations．With the array system，the azimuths and the apparent
velocities of incoming waves are easily determined and these parameters，with S-P times，
enable epicenters to be
determined quickly．
In emergencies，the MSO
thus serves，with the
functions of this array
system，as a backup for
the JMA Headquarters in
Tokyo．