**2.4 Discussions of chain reaction effect on slow earthquake migration**

Fig. 5 clearly shows that only slow slip events occur at depth of 30 km where frictional property is slightly stable and uniform along strike, while various slow earthquakes including very low-frequency events (orange color in Fig. 5) are generated by chain reaction between small asperities. This result suggests that chain reaction model as shown in Fig. 1 can explain various types of slow earthquakes occur in the same region.

Fig. 7 shows that MA has recurrence interval longer than that of SA, which is also seen for migration distance. These results may suggest that we can estimate asperity size on the basis of migration distance and recurrence interval of slow earthquakes.

For example, migration of low-frequency tremor observed in Kii and Tokai area tends to be unilateral with longer travel distance and loger recurrence interval of slip events, while the tremor in Shikoku tends to be shorter recurrence interval and shorter travel distance (e.g., Obara, 2010). These results suggest that size of asperities generating slow earthquakes in Kii and Tokai is larger than that in Shikoku. Therefore, investigating slow earthquake migration process is important to estimate the characteristics of small asperities.
