Abstract
We estimate the three-dimensional (3D) P-wave attenuation structure beneath the Niigata–Kobe Tectonic Zone (NKTZ), central Japan, using high-quality waveform data from a large number of stations. The obtained results confirm the segmentation of the NKTZ into three regions, as suggested by 3D seismic velocity models, and reveal characteristic structures related to surface deformation, shallow subduction of the Philippine Sea slab, and magmatism. The lower crust beneath the NKTZ west of the Itoigawa–Shizuoka Tectonic Line (ISTL) is overall characterized by distinct high attenuation, whereas the upper crust shows marked high attenuation to the east of the ISTL. Differences in the depths of anelastically weakened parts of the crust probably result in a first-order spatial variation in surface deformation, forming wide (width of ~100 km) and narrow (width of 25–40 km) deformation zones on the western and eastern sides of the ISTL, respectively. Many M ≥ 6.5 earthquakes occur in the upper crust where seismic attenuation in the underlying lower crust varies sharply, suggesting that spatial variations in rates of anelastic deformation in the lower crust result in stress concentration in the overlying brittle crust. We interpret a moderate- to low-attenuation zone located in the lower crust at the northeast of Biwa Lake to reflect low-temperature conditions that are developed locally as a result of shallow subduction of the cold Philippine Sea slab.Graphical .
Highlights
The Niigata–Kobe Tectonic Zone (NKTZ) is a geodetically derived high-strain-rate zone that extends for ~500 km (NE–SW) across central Japan (Sagiya et al 2000)
The high strain rates were first interpreted based on kinematic models, such as a detachment model (Hirahara et al 1998) and collision models (e.g., Shimazaki and Zhao 2000; Heki and Miyazaki 2001), but these models are unlikely to produce the NKTZ due to the implausible physics required to produce the combination of the observed stress field, inferred mantle flow, and observed fault movement (Iio et al 2002)
Shear-wave splitting analysis of the upper crust suggests that the high strain rates at the surface west of the Itoigawa–Shizuoka Tectonic Line (ISTL) are caused by high deformation rates below the Nakajima and Matsuzawa Earth, Planets and Space (2017) 69:33
Summary
Attenuation term and site amplification factor For the earthquakes with fc estimates, we calculated P-wave and noise spectral amplitudes from vertical component of velocity seismograms with a window length of 2.56 s after and before the P-wave onset, respectively. The resolution of the uppermost mantle is not sufficient to discuss the observed attenuation structure, as a result of an insufficient number of rays propagating at depths >60 km, where the recovery of the checkerboard resolution tests is not good (Fig. 4b; Additional file 1: Figure S1)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
