Fig. 4

A comparison between slip rates and seismicity. a The red solid line denotes the annual average of the slip rate in Fig. 2g, where the tidal and non-tidal effects are considered. The result is given in units of the rate of stress change by multiplying the slip rates by an elastic constant, based on Eq. (2). A 5-year running average is also superimposed to emphasize the decadal variations. The blue curve denotes the annual average of the rate of stress change, computed from the slip rate shown in Fig. 2d, where only the tidal effects are considered. The yellow circles denote the background seismicity, inferred by the method of Ide (2013). The employed earthquakes are shown in Fig. 1c,d. The superimposed pink bars denote periods of large-scale meandering of the Kuroshio Current, as in Fig. 3b, during which the seismicity seemed to decrease. When excluding non-tidal effects, the increase in seismicity during the mid-1990s cannot be explained. b The horizontal and vertical axes denote months and slip rate, respectively. The red and blue symbols denote the monthly averages in Fig. 2h,e, respectively, from 1980 to 2013, which are plotted cyclically against months. The green line represents the frequency of great historical earthquakes in the Tokai area (1605, 1707, and 1854), for which Mogi (1969) noted the seasonality. c The red and blue curves denote the stress changes obtained by integrating the rates in Fig. 2g with respect to time. The purple bars show the periods when four long-term slow slip events occurred in the Tokai area (Kobayashi 2014; Geographical Information Authority of Japan 2015). d The red and blue curves denote the slip rates for cases including and excluding non-tidal effects, respectively, when A − B is assumed to be negative (see text). The purple bars show the periods of the SSEs