15:30 〜 16:30
[J05-P-14] Spatio-temporal variation in Coda Q in the northeastern part of Niigata-Kobe Tectonic Zone in 2009-2014
We focus on a high strain rate zone called Niigata-Kobe Tectonic Zone (NKTZ) (Sagiya et al., 2000) to understand a stress accumulation process in seismogenic zone. Jin and Aki (2005) showed that low coda Q at low frequency bands corresponded spatially to the high strain rate zone. Hiramatsu et al. (2013) and Tsuji et al. (2014) suggested that the cause of the high strain rate zone was attributed to the high deformation rate below the brittle-ductile transition zone in the crust in the central part of the NKTZ. This study investigates details of the spatial distribution of coda Q in the northeastern part of the NKTZ. We have analyzed 646 events from January 2009 to February 2011 (period I) and 2194 events from January 2012 to October 2014 (period II).
We compare the data between the periods I and II. We applied t tests to analyze these temporal variations and recognize that the variations are not statistically significant. These facts imply that the temporal variation in coda Q caused by the 2011 earthquake is not significant in this study area.
The spatial distributions of coda Q at the 2-4 and 4-8 Hz frequency bands for periods I and II are found to be negatively correlated with the differential strain rate (Sagiya et al., 2000; Nishimura 2015, personal communication). Positive correlations are found between the perturbation of the S-wave velocity (Nakajima and Hasegawa, 2007) at 25 km depth and coda Q at the low frequency bands, and between the perturbation of the S-wave velocity at 10 km depth and coda Q at the middle frequency bands for both the periods in this study area. These facts imply that the spatial distributions of coda Q at the low and middle frequency bands reflect mainly the heterogeneity of the lower crust and the upper crust, respectively. We suggest that the deformation in the upper crust, as well as the ductile deformation in the lower crust, may be a dominant cause of the high strain rate in the northeastern part of the NKTZ.
We compare the data between the periods I and II. We applied t tests to analyze these temporal variations and recognize that the variations are not statistically significant. These facts imply that the temporal variation in coda Q caused by the 2011 earthquake is not significant in this study area.
The spatial distributions of coda Q at the 2-4 and 4-8 Hz frequency bands for periods I and II are found to be negatively correlated with the differential strain rate (Sagiya et al., 2000; Nishimura 2015, personal communication). Positive correlations are found between the perturbation of the S-wave velocity (Nakajima and Hasegawa, 2007) at 25 km depth and coda Q at the low frequency bands, and between the perturbation of the S-wave velocity at 10 km depth and coda Q at the middle frequency bands for both the periods in this study area. These facts imply that the spatial distributions of coda Q at the low and middle frequency bands reflect mainly the heterogeneity of the lower crust and the upper crust, respectively. We suggest that the deformation in the upper crust, as well as the ductile deformation in the lower crust, may be a dominant cause of the high strain rate in the northeastern part of the NKTZ.