We have analyzed the spatial variation in coda Q in the northeastern part of a high strain rate zone, the Niigata-Kobe Tectonic Zone (NKTZ), to investigate the cause of the high strain rate by correlating coda Q with the differential strain rate and the S-wave velocity. The spatial distributions of coda Q in the 2-4 and 4-8 Hz frequency bands are found to be negatively correlated with the differential strain rate. Coda Q in the 2-4 Hz frequency band is correlated spatially with the S-wave velocity at a 25 km depth, as has been reported previously. We also find a positive correlation between the perturbation of the S-wave velocity at a 10 km depth and coda Q in the 4-8 Hz frequency band, implying that the spatial distribution of coda Q in this frequency band is mainly attributed to the heterogeneity of the upper crust. This feature is different from that of the central part of the NKTZ reported previously, which indicates a difference in the cause of the high strain rate. Therefore, we suggest that the high deformation rate in the upper crust, which is characterized by a thick sediment basin, as well as that in the ductile lower crust, contributes to the generation process of the high strain rate on the surface in the northeastern part of the NKTZ.

We have analyzed the temporal variation in coda Q in the northeastern part of an inland high strain rate zone, the Niigata-Kobe Tectonic Zone (NKTZ), in central Japan, to investigate the response of coda Q to the modification of the strain field induced by the 2011 Tohoku earthquake (Mw 9.0). We observe no statistically significant temporal variations in the spatial distribution of coda Q as the whole analyzed area, implying that the crustal deformation induced by the 2011 Tohoku earthquake has provided no significant temporal variation in crustal heterogeneity as the whole analyzed area. For the middle frequency bands, before and after the 2011 Tohoku earthquake, we have commonly found a negative correlation between the spatial distributions of coda Q and the differential strain rate and a positive correlation between the spatial distributions of coda Q and the perturbation of S-wave velocity in the upper crust. These features, together with previous works, suggest that the ductile deformation with a high rate in the upper crust plays an important role in generating the high strain rate in the analyzed area not only before but also after the 2011 Tohoku earthquake. In other words, the existence of a persistent ductile deformation in the upper crust contributes essentially to the generation process of the high strain rate in the northeastern part of the NKTZ. It is important to note that the location of the persistent ductile deformation in the northeastern part of the NKTZ, mainly in the upper crust, differs from that in the central part of the NKTZ, mainly in the lower crust. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.