[S-CG39] Science of slow earthquakes: Toward unified understandings of whole earthquake process

[SCG39-P11] Tectonic tremors influenced by characteristic of structure and pore pressure in the Nankai subduction zone, Japan

*Andri Hendriyana¹、Takeshi Tsuji^2,3,4 (1.Geophysical Engineering, Institute of Technology Bandung, Indonesia、2.International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, Fukuoka, Japan、3.Department of Earth Resources Engineering, Kyushu University, Fukuoka, Japan、4.Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan)

キーワード：tectonic tremor, source estimation, tremor migration, pore pressure, Nankai trough

Episodes of tectonic tremor are observed in the Nankai accretionary prism close to the trough axis; however, their non-impulsive signals and the distortion of seismic signals in the accretionary prism make it challenging to accurately estimate their locations. Reliable tremor locations would help to characterize geological conditions favourable for tremor generation. Here we report a new approach to pinpoint tremor locations based on seismic phase polarization. The estimated epicentres of tremor distribution mostly coincide with low velocity shear zone or thick underthrust sediments where high pore pressures are inferred, and the distribution of tremor appears to be controlled by characteristics of the shear zone. A tremor episode occurred a couple days after the off-Mie earthquake clearly shows migration. Migration of tremor initiated around the outer ridge where the estimated pore pressure is greatest. The spatio-temporal tremor distribution indicates that pore pressure relaxation could trigger the tremor migration. The occurrence of tremor thus may indicate a weak shallow plate interface that is prone to slip following large earthquakes. Based on the information of tremor migration, the permeability along the fault can be estimated as 3.7 × 10 –12 m2 .