地震動のやや長周期成分からみた1923年関東地震の震源特性

その2 断層モデルに基づく高田測候所での地震動記録の再現

抄録

Records observed at the Takada observatory by an Imamura's type strong motion seismograph are useful in Japan to investigate a source process of the 1923 Kanto earthquake (M=7.9). Ground motion in the vertical component is completely recorded to the end. Those in horizontal components are also recorded to the end, though the amplitudes of them are saturated in the midst of the records. The instrumental response of the seismograph has been already clarified by TAKEMURA and NOZAWA (1996), and many records from the recent earthquakes occurring near the focal region of the Kanto earthquake are also obtained at the same site with modern instruments. First, a crustal structure model from the source to the station is established so as to explain the dispersion characteristics of Love-waves observed for the recent earthquakes, and their records are simulated by the normal mode theory using the obtained structure to confirm its validity. Secondly, the records from the Kanto earthquake are reproduced using the same structure model. NOZAWA et al. (1995) proposed the two possible source models for the Kanto earthquake through the simulation of the records at the Gifu observatory. Two big subevents with a time interval of about 12s are assumed on the fault plane in both the models, while the focal mechanism and the focal depth of the second subevent are different between these models. It is found that these models similarly explain the records at the Takada observatory from the Kanto earthquake. The maximum displacements of the reproduced horizontal ground motions are estimated about 20cm in NS component. and about 10cm in EW component. These results are consistent with the fact that the amplitudes of the records in NS component are strongly saturated compared with those in EW component.