[S07-P] Poster

[S07-P-02] Source effects of intraslab and interplate earthquakes off Miyagi Prefecture in Northeastern Japan and their relation to source depths

^○Yasumaro Kakehi (Kobe University, Kobe, Japan)

Two different views have been presented as to the source effects (especially, the high-frequency level of acceleration spectrum) of intraslab and interplate earthquakes: (a) high-frequency level of intraslab earthquake is higher than that of interplate earthquake, and (b) high-frequency level depends simply on source depth, independent of tectonic environments, and high-frequency level is higher for deeper source. Kasatani and Kakehi (2014) (hereafter, KK) made spectral inversion analysis of the intraslab and interplate earthquakes off Miyagi Prefecture in Northeastern Japan using K-NET strong ground motion data of NIED. Their result supported (b). In this study, three events are selected from the events KK studied, and their strong ground motion data are analyzed. They are composed of two shallow events: S1 (intraslab, Mw 5.5, 35.94 km) and P (interplate, Mw 5.0, 42.86 km), and one deep event: S2 (intraslab, Mw 5.5, 83.10 km). In the comparison of attenuation relations of acceleration amplitudes, the slope of decay of deep S2 is obviously steeper than those of shallow S1 and P. On the other hand, in the spectral inversion of KK, common attenuation relation is assumed for all the events, independent of source depths. Actually, the attenuation relations of the acceleration amplitudes with the site effects (obtained in the spectral inversion) removed shows similar gentle slope of decay for all of the three events. This means that in the spectral inversion of KK, the strength of attenuation is underestimated for deeper events, and therefore, the high-frequency level of source is also underestimated for deeper events. When the steep decay of for deeper events are considered, high-frequency levels of deeper events will be higher than those obtained in KK, and the difference of high-frequency levels between shallow and deep events will become larger and more clear. This enhances the validity of the conclusion of KK that high-frequency level is higher for deeper source.