Abstract
Measured seismic intensity data have been observed densely during many recent earthquakes in Japan. We have constructed seismic intensity database and analyzed the characteristics of attenuation and local site correction regarding short-period ground motions in various regions of Japan. It is found that the local site correction for seismic intensity is dependent on earthquake magnitude in the case of the Kanto plain. The regression analysis indicates that there is positive correlation at lowlands such as the east of Saitama and negative correlation at hilly areas such as the south of Chiba between the intensity coefficient for local site correction and magnitude. Using the obtained attenuation formula of seismic intensity and the intensity coefficient for local site correction, the intensity inversion analyses were carried out and the short-period seismic wave radiation zones (SPRZ) were identified for the Great Kanto earthquake in 1923 and the Genroku earthquake in 1703. The result shows that there were two separate SPRZs in east-and-west both sides across the Miura peninsula during the Great Kanto earthquake. The both of energy centroids of the SPRZ correspond to the terminus part of large slip areas derived from the existing waveform inversion study. The SPRZs of the Genroku earthquake are similar to those of the Great Kanto earthquake as for the areas from Kanagawa to the south of Chiba. In addition to those, the SPRZ is deduced to spread southeastward off the Boso peninsula.
