[SSS17-P08] Estimation of seismic motion at depth from records at a ground surface station without assumption of plane wave incidence
Keywords:seismic motion, plane wave, strong motion, subsurface wavefield
In this study, we apply the new method to real event records which were observed both at surface and subsurface levels and compare the estimated seismogram by our method with the subsurface record and one obtained by the conventional method to confirm effectiveness of our method. We employ the local strong-motion records at a KiK-net, NIED station in western and central Tottori. We could successfully recover the subsurface records by our method. Fig. 2 shows the comparison of the velocity waveforms at depth of 100 m estimated by the proposed and the conventional methods for the evaluation point with a horizontal offset of 1 km from the surface station. Red and green lines indicate the seismograms estimated by the proposed and the conventional methods, respectively. They have a clear difference in the phase. If the evaluation point is located at a deeper position, each waveform differs both in the phase and the amplitude. This is because the conventional method is not able to consider the effect of the oblique incidence. The proposed method is also very robust to errors in the assumed focal mechanism and the structure model deeper than the evaluation point, and sensitive to the used shallower structure model. We will further discuss about the spectra in the frequency domain and the relationship between the estimated waveform and the shallow structure.