**3.3 Comparison of slow earthquakes between simulation and observational results**

Fig. 9e shows that a large aseismic slip event occurs locally between LA and the SA belt (indicated by the ellipse) approximately one year before the megathrust earthquake. The spatiotemporal region enclosed by the ellipse in Fig. 9b shows that the large aseismic slip event triggers slow earthquakes in the SA belt with a shorter recurrence interval compared to other areas (|Strike| > 20 km). The migration distance in the SA belt corresponds to the size of the large aseismic slip region (|Strike| < 20 km). This behavior is similar to the longterm SSE (slow slip event) observed at Bungo Channel in 2003, where nearby LFT (low frequency tremor) migration had occurred either at a shorter recurrence interval or nearly continuously for several months (Obara, 2010). Therefore, the activity of the LFTs may be useful to estimate the duration and the location of local aseismic slip events, such as the long-term SSE and the preseismic slip in the deeper part of LA.

As pre- and post-seismic changes, intense LFT activity began to occur almost directly below the 2004 Parkfield earthquake about three weeks before the earthquake and has continued only apart from the hypocenter over for four years (Nadeau & Guilhem, 2009; Shelly, 2009), which means that the distance from the hypocenter of triggering earthquake may also affect the sensitivity of LFT to pre- and post-seismic slip (Shelly, 2009).

Our simulation shows that the moment release rate of slow earthquakes near the locked region of LA becomes higher about one month before the megathrust earthquake as mentioned in the section 3.2, and Figs. 9ab show that a shorter recurrence interval of slow earthquakes in the SA belt occurs several years after the megathrust earthquake. These simulation results are consistent with those results observed in Parkfield for the pre- and post-seismic stages of nearby large earthquakes.

Since SSE, pre- and post-seismic slips are all transients of interplate-slip faster than *V*pl, the observations reported by Obara (2010), Nadeau & Guilhem (2009), and Shelly (2009) would support our suggestion that the preseismic slip of megathrust earthquakes can be practically detected by monitoring slow earthquake migrations, even if the actual *dc* is less than several centimeters.
