HR: 0800h
AN: S21B-0212    [Abstracts]
TI: Long-Period Strong Ground Motions Having Fired Large Oil Storage Tanks During the 2003 Tokachi-Oki, Japan, Earthquake
AU: * Hatayama, K
EM: hatayama@fri.go.jp
AF: National Research Institute of Fire and Disaster, 3-14-1, Nakahara, Mitaka, Tokyo, 181-8633 Japan
AB: The 2003 Tokachi-oki, Japan, earthquake (Mw8.0; Japan Meteorological Agency, 2003) generated large-amplitude long-period (5 to 8 sec) strong ground motions in the Yufutsu plain, Hokkaido, Japan that is about 200 km away from the epicenter. Those motions excited big sloshing in many large oil storage tanks located on the plain and the sloshing caused two tank fires and several floating roofs to sink. Japanese nation-wide strong-motion observation networks have provided us with the first data set consisting of densely sampled strong ground motions that are rich in long-period components. This data set clearly showed that the large long-period motions were not observed before the waves entering the plain, i.e. the Yufutsu plain grew the long-period ground motions (Koketsu et al., 2005). The high density of spatial sampling can also show the spatial distribution of strength of long-period motions in the plain and their propagation there. We show by some contour maps of velocity responses that the strongest long-period shaking in the Yufutsu plain was observed around the downtown area of the Tomakomai city where the damage to oil tanks was more severe than any other areas. The isochrone of peaks of envelopes suggests a possibility that the long-period wave trains were focusing into the downtown from different directions. In order to study the excitation and the propagation process of long-period motions in the Yufutsu plain, an attempt was made to explore its deep sediment-bedrock structure by means of long-period microtremor array observations (Kanno et al., 2005). Relying on their resultant S-wave velocity profiles, we try to reproduce the features of the long-period motions observed there during the 2003 Tokachi-oki earthquake by making numerical simulations of 2-D seismic wave-fields by means of the finite difference method. To date we have succeeded in reproducing qualitatively the observed phenomena that the amplitude of long-period motions in the downtown area of the Tomakomai city was larger than any other areas in the Yufutsu plain.
DE: 7212 Earthquake ground motions and engineering seismology
SC: Seismology [S]
MN: Fall Meeting 2005