Fig. 4

Results of a checkerboard resolution test for phase velocity distributions. We calculated the synthetic data from input checkerboard models with 8 % anomalies at a period of 80 s: a, d input models, b, c, e, f output models. Cell sizes are 5° and 3° in (a–c) and (d–f), respectively. Correlation length is 100 km in (b, e) and 200 km in (c, f). Broken lines show the region of the superswell defined by depth anomalies greater than ~300 m. Open triangles indicate the stations, and green diamonds indicate active hotspots. Green rectangle outlines the “Society region,” where a correlation length of 100 km is applied in Fig. 5