[S-SS09] Strong Ground Motion and Earthquake Disaster

[SSS09-01] Azimuthal characteristics of residuals of spectral inversion analyses

*Tomonori Ikeura¹ (1.Kajima Technical Research Institute)

Keywords:spectrum inversion, regression residuals, azimuth dependency characteristics

I proposed an attenuation model of strong motions considering transmission coefficient of direct S-waves in the layered structure, and applied it to strong motions due to inland earthquakes in Kinki, Fukushima Hamadori and northern Ibaraki and Chugoku regions. Though the results showed better performance especially in the near source regions than usual methods, the rms errors of the estimation results remained about 0.4 in natural logarithm. In order to decrease the rms errors, it is necessary to consider not only attenuation characteristics but also azimuthal characteristics of radiated waves from the sources. I examined azimuthal characteristics of residuals of 28 inland earthquakes in the above three regions, and found systematic change in azimuth due to focal mechanism and/or rupture directivity in the low frequency residuals of some of the events. To interpret the azimuthal changes, I estimated an apparent rupture direction and rupture velocity every event by a grid search, fitting an azimuthal model of the radiation pattern and the rupture directivity function to the azimuthal distributions of the residuals. The results shows that the azimuthal model explains residuals in the lower frequencies well, indicating a vaildity for decreasing rms error of strong motion prediction models.