Study on temporal change of attenuation structure in the the inland earthquake's source region

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Tsumura et al.(2012) mapped a seismic attenuation (Qp) structure in the source region of the 2007 Noto Hanto earthquake. The results show low Qp zone is seen at the main shock fault, where aftershocks' activity is high. Next we made Qp/Qs estimation for several ray paths by using spectral ratio method. Obtained Qp/Qs for the low Qp zone in the main shock fault is higher than that of the surrounding area. In conjunction with other geophysical data, these attenuation features might be caused by the rupture of the main shock.To detect the temporal change of seismic structure near the source region, we made the other temporary seismic observations in 2011 and in 2012. In these observations, we set seismic stations, whose locations were same as those of 2007 observation. The result for 2011 and 2012 observation data shows that ray paths having high Qp/Qs concentrated on the west coast area of Noto Peninsula where high Qp/Qs was observed in 2007, and temporal change of Qp/Qs was not clear.