PREDICTING JMA SEISMIC INTENSITIES BASED ON 3-D ATTENUATION STRUCTURE AND SURFACE AMPLIFYING FACTOR

THE TOHOKU DISTRICT, JAPAN

抄録

Predictions of seismic intensities are attempted based on a three-dimensional attenuation structure and amplifying factors at stations obtained in the previous study for the Tohoku district, Japan. An empirical relation between `earthquake size' related to the intensity and JMA magnitude M_J is also used. The first prediction is to map spatial distribution of the minimum magnitude M_J of an earthquake which causes intensity 5 at a specific JMA station. The result shows that the effects of regional variation of attenuation and local site condition at the station are important in assessing the seismic hazard. Another attempt is made to predict an annual number of felt earthquakes at each JMA station based on the JMA earthquake catalogue for a period from 1963 to 1984. A comparison of predicted number with the observed one shows a good coincidence between them for each year. This may suggest that the proposed method can successfully predict intensities. However, a comparison of the predicted cumulative number for each intensity grade with the observed one shows that the cumulative numbers for intensities 2, 3, and 4 are underestimated by the proposed method. This result may suggest a nonlinearity between the JMA intensity scale and the logarithm of acceleration, which has been suggested by other evidences.