[S-CG45] Science of slow-to-fast earthquakes

[SCG45-P35] 南海トラフにみられる深部テクトニック微動の潮汐法線応力に対する応答

*生田 領野¹、小野田 諒平² (1.静岡大学理学部、2.静岡大学大学院総合科学技術研究科)

キーワード：深部テクトニック微動、南海トラフ、潮汐感度

Deep tectonic tremors in the Nankai trough occur in the transition zone between the seismogenic and stable sliding zones along the subducting plate interface. Because tremors change their activity with time in the transition zone, tremors can provide us some information about the frictional characteristics and stress state of the plate interface. The tremors are sensitive to stress disturbances and are known to occur in response to tides. Several previous studies have reported the stress sensitivity of tremors in the Nankai trough by calculating tidal stresses on the fault. In the previous studies, some tremors are highly sensitive to normal stresses (Ide & Tanaka, 2014) and some to shear stresses (Yabe et al., 2015). In this study, we estimate the tidal sensitivity of tremors in the Nankai trough for 20 years from 2001 to 2020 to DCFF (Coulomb failure function) stress which considers the friction coefficient balancing between the normal and shear stresses using TidalStrain2 (Hirose et al., 2019). As a result, the sensitivity of tremor to the tidal shear stress in the plate convergence direction is roughly consistent with the results of previous studies with high tidal sensitivity. In some region, the sensitivity to DCFF is largest with high friction coefficient up to 0.6. The tremors occur responding to changes in normal stress as well as shear stress. We will discuss the spatiotemporal distribution of the sensitivity of tremor to tidal normal stress.

References:
Hirose, F., Maeda, K., & Kamigaichi, O. (2019). Tidal forcing of interplate earthquakes along the Tonga-Kermadec Trench. Journal of Geophysical Research: Solid Earth, 124, 10,498-10,521. https://doi.org/10.1029/2019JB018088.
Ide, S., and Y. Tanaka (2014), Controls on plate motion by oscillating tidal stress: Evidence from deep tremors in western Japan, Geophys. Res. Lett., 41, 3842–3850, doi:10.1002/2014GL060035.
Yabe, S., Y. Tanaka, H. Houston, and S. Ide (2015), Tidal sensitivity of tectonic tremors in Nankai and Cascadia subduction zones, J. Geophys. Res. Solid Earth, 120, 7587–7605, doi:10.1002/2015JB012250.