短周期の表面波

1965年弟子屈付近の地震

抄録

Surface waves of short periods were finely found on the records of three Teshikaga earthquakes in 1965. The observation point was Kushiro in Hokkaido and the seismometer used was Type 59 of J. M. A.. The magnitudes of these earthquakes were about 5 and the epicentral distances were between 50 and 60km. The EW-component of the seismometer recorded Love waves and the NS- and the vertical components recorded Rayleigh waves, because the direction propagated by these surface waves was nearly north to south. Three modes, M₁₁, M₁₂ and Love were identified on the records and group velocities of them were obtained from these records. Only three models of the crustal structure are given in the present paper, though much more models were examined numerically. One of the successful models, HOK-5 B, has the sedimentary layer whose thickness is 2.25km.