Map showing the distribution of permanent ocean-bottom seismic stations off the Kii Peninsula. Dark gray triangles with station codes indicate the locations of DONET stations and light gray squares the locations of DONET science nodes; the black square is the landing station. The eight DONET stations installed by January 2011 are indicated by their codes on a gray background. Thick lines indicate the optical fiber cables connecting the DONET stations and the landing station. Light gray diamonds represent the locations of the permanent OBS stations deployed by JMA. Gray contours indicate the ocean-bottom topography. The line with triangular “teeth” indicates the estimated location of the Nankai trough axis. The rectangle enclosed by dashed lines is the area shown in Figs. 3, 5, 6, and 8. The inset shows the location of the plotted area in Japan.