Fig. 1: Tectonic setting of the Hyuga-nada area.
From: Upper-plate conduits linked to plate boundary that hosts slow earthquakes
a Regional bathymetric map of the study area. Purple, blue, and green shaded areas indicate the source areas of large megathrust earthquakes in 194647, 196812, and 199613, respectively Orange shades indicate the source areas of slow slip events14,48. White dots, yellow squares, and red triangles denote the locations of low-frequency tremors14, repeating earthquakes38, and mud volcanoes20,21,22, respectively. The convergence direction of the Philippine Sea Plate relative to the Amurian plate is shown by the white arrow28. The thin black line indicates the seismic profile of this study, and the thick black line indicates the range shown in Figs. 2, 4 and 5. The black box indicates the location enlarged in panel b. b Layout of the ocean bottom seismographs (OBSs) and multichannel seismic (MCS) reflection profiles superimposed on the reduced-to-pole (RTP) magnetic anomaly map49. The yellow circles indicate the locations of OBSs. The MCS reflection data were acquired along the black line. The velocity model and reflection images shown in Fig. 2 correspond to the 100-km-profile where the OBSs were deployed.
