Our purpose is not to obtain equally spaced trench segments.
A similar lateral variability in rupture mode at individual trench segments is found in the Sumatra-Andaman subduction zone (Stein and Okal, 2007).
Some arc geometry analysed in this paper, i.e. the Caribbean and Banda arcs, or other trench segments where active volcanoes are located are not in the database from Hayes et al. (2012).
We consider the slab dip directions worldwide, from the Slab 1.0 database (Hayes et al. 2012), and we computed the mean azimuth of the normal lines to the trench segments.
The difference between these two types of segmentations is that strongly-coupled areas of trench-ward segments give rise to ADDS, whereas almost 100% coupled areas of shallow parts of the subduction zone give rise to ASSS.
The double segmentation in the To-hoku district is due to the apparent absence of earthquakes, historically, in the trench-ward segments, in contrast to the smaller (up to Mw 7.5) earthquakes that repeatedly break the deeper, Japan Island-ward segments.
Even taking the limitation of event detectability only by observations on land into consideration, we can see virtually no seismicity in segments close to the trench such as Segments C′ and D′.
