Influence of structure and pore pressure of plate interface on tectonic tremor in the Nankai subduction zone, Japan

• Published in: Earth and planetary science letters 2021-03, Vol.558, p.116742, Article 116742
• Main Authors: Hendriyana, Andri, Tsuji, Takeshi
• Format: Article
• Language: English
• Subjects: Nankai Trough; plate boundary decollement; pore pressure; source estimation; tectonic tremor; tremor migration
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2021.116742

•Propose an alternative workflow to estimate location of many tectonic tremors.•Tremor could be in shear zone or underthrust sediments on the plate boundary.•Thickness of the shear zone or underthrust sediments could control tremor epicentre.•Pore pressure diffusion is a likely mechanism for tremor migration.•Identify migration speed of tectonic tremors and estimate permeability of fault. 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 and could offer insights into the up-dip limit of coseismic ruptures. 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 at a velocity similar to that of very low frequency earthquakes. 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.