- 公益社団法人 日本地震学会
- 地震 第2輯 (ISSN:00371114)
- vol.50, no.4, pp.377-396, 1998-03-13 (Released:2010-03-11)
Strong ground motion in Tokyo metropolis during the Sep. 1, 1923 Kanto earthquake was important factor for determining the seismic design code in Japan. However, it has not been clarified in detail, because of no strong motion record near the source region of the Kanto earthquake. The author collected the descriptions and made a data set of 548 personal experiences in and around the southern Kanto district to investigate the strong ground motion from the Kanto earthquake. Many descriptions in Tokyo metropolis indicated that three severely strong shakings arrived at this area during the Kanto earthquake. The first shaking was, of course, caused by the main shock (M=7.9) at 11:58AM (JST). The second and the third shakings were caused by the aftershocks occurring 3 minutes and 4.5 minutes after the main shock, respectively. These aftershocks were identified on a seismogram obtained at Gifu observatory and magnitudes of them were determined to be 7.2 and 7.3, respectively from this seismogram [TAKEMURA (1994)]. The results of the analyses of the personal experiences also indicated that the duration time of the first shaking due to the main shock was 30 to 40sec. The strength of the second shaking was as strong as the first shaking, of which seismic intensity was estimated to be VI in JMA scale, while duration time of the second shaking was shorter than the first shaking. On the other hand, the third shaking was weaker than the first and the second shakings, of which seismic intensity was estimated to be V. The sequence of strong shakings within 5 minutes after the occurrence of the main shock of the 1923 Kanto earthquake was elucidated in Tokyo metropolis in the present study.