Spatial variation in coda Q and stressing rate around the Atotsugawa fault zone in a high strain rate zone, central Japan

Abstract

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.

Anelastic properties beneath the Niigata–Kobe Tectonic Zone, Japan

“…Nakajima and Hasegawa (2007) discussed the origin and segmentation of the NKTZ on the basis of seismic velocity structures and suggested that the crustal structure west of the ISTL differs from that east of the ISTL. Jin and Aki (2005) reported a narrow, conspicuous lowcoda attenuation zone west of the ISTL at frequencies less than 4 Hz, whose existence was later corroborated by Carcole and Sato (2010) and Hiramatsu et al (2013). Shear-wave splitting analysis of the upper crust suggests that the high strain rates at the surface west of the ISTL are caused by high deformation rates below the Open Access *Correspondence: nakajima@geo.titech.ac.jpbrittle-ductile transition zone (Hiramatsu et al 2010).…”