We investigate a detailed spatial variation in shear wave splitting in the zone of inland high strain rate, called the Niigata-Kobe Tectonic Zone (NKTZ), central Japan. Most observations show stress induced anisotropy, that is, the orientation of the faster polarized shear wave is parallel to the axis of the maximum horizontal compressional strain rate estimated from GPS data. Others show structure induced anisotropy, that is, the orientation is parallel to the strike of active faults. For the stress induced anisotropy, time delays normalized by the path length in the anisotropic upper crust is proportional to the differential strain rate. We estimate a spatial variation in stressing rate of the upper crust beneath the high strain rate zone based on a response of the normalized time delay to a step-wise stress change caused by a moderate-sized earthquake. The variation in the stressing rate of 3 kPa/year estimated from shear wave splitting is coincident with that from GPS data. We conclude, together with other seismological features in the NKTZ reported previously, that the high strain rate in the NKTZ is attributed to the high deformation rate below the brittle-ductile transition zone in the crust.

We investigated a detailed spatial distribution of coda Q around the Atotsugawa fault zone in a high strain rate zone, central Japan, using waveform data from dense seismic observations. Low coda Q at lower frequencies is localized along the fault zone, showing a good spatial correlation with a low velocity zone in the lower crust. On the other hand, we find no characteristic spatial pattern of coda Q at higher frequencies. The spatial correlation between the low coda Q at the lower frequencies, and the low velocity zone, suggests that ductile deformations below the brittle-ductile transition zone in the crust contribute to the variation in coda Q at lower frequencies. We estimated a spatial variation in the stressing rate of 15-18 kPa/year in the crust from that of coda Q in the analyzed region. This value is greater than that estimated from GPS data. We conclude, therefore, that a high deformation rate below the brittle-ductile transition zone causes the high stressing rate, which results in the high strain rate along the fault zone observed by GPS.