In connection with the Matsushiro swarm earthquakes that began in August 1965, the Earthquake Research Institute, University of Tokyo, conducted continuous observation of tilting of the ground at Matsushiro. Two components of a water-tube tiltmeter 40 meters in length and two components of a horizontal pendulum tiltmeter were installed in a vault of the Matsushiro Seismological Observatory of the Japan Meteorological Agency in the outskirts of the town of Matsushiro.
We observed very large changes in the inclination of the ground. The changes were greatest in the third stage of seismic activity, the speed of tilt reaching 0.7 inch per day. Since these changes were strongly correlated with seismic activity, tiltmeter observation provided powerful data for a long-range estimate of seismic activity.