Fig. 5

Relationship between normalized distance (distance between the centroids of a pair of earthquakes divided by the summation of the source radii) and coherence for the off-Kamaishi earthquake cluster in northeastern Japan (Fig. 4a). a, b The results from the frequency range around the corner frequency of the smaller earthquake (1/2 fc–2 fc) (Uchida and Matsuzawa 2013) and 1–2 Hz, respectively. Normalized distances 0, 1, and > 1 indicate identical centroids, contacting sources, and sources with no overlap as shown in top left insets. Black dots show values at each station and colored dots are values averaged for each pair of earthquakes. The color represents the radius ratio (the radius of the smaller earthquake divided by the radius of the larger earthquake). The centroid locations and source sizes used for the calculations are from Uchida et al. (2012) where the centroids are estimated by the waveform-based double-difference method and the source sizes are estimated from corner frequencies using stacked spectrum ratios. Uncertainties in the normalized distance and radius ratio are less than 0.2 and 0.12, respectively