震度観測装置による松代地震の震度測定

抄録

An instrument was deviced, which determines the earthquake intensity mechanically, and put into a trial observation in the Matsushiro Seismological Observatory from July, 1967 for the Matsushiro swarm earthquakes. The instrument employs a 3cps vertical transducer of moving coil type, and its output, corresponding to the relation between intensity scale and ground acceleration proposed by the Japan Meteorological Agency. The present paper reports the comparison between two intensities obtained by the conventional method and by the instrument, considering parameters such as epicentral distance, depth, azimuth and magnitude.
The results are summarized in the following.
1) Coincidence was found between two intensities for 48% of perceptible earthquakes. Whether two intensities coincide or not has no corelation to S-P time, depth/epicentral distance, azimuth or magnitude.
2) A coincidence coefficient of 59% was obtained for earthquakes of intensity I, II and III, which were the majority of the observed earthquakes.
3) 69% of earthquakes of discrepant intensities gave 0 for instrumental intensity and 1 for empirical intensity. Combinations of 0-I and 1-I have no definite correlation to the earthquake magnitude.
4) Vertical ground accelerations of less than 0.8gal are still perceptible to human bodies. By making the lower limit of the perceptible acceleration smaller, most of the discrepant cases can be eliminated.
5) Earthquakes of intensity I give sometimes considerably high ground acceleration; however, its period is very short.
We hope a more comprehensive instrument is developed, which determines the earthquake intensity, by introducing horizontal components and improving the criterion between intensity and acceleration.