Image of Earthquake as Plate Tectonics

Plate Tectonics theory is the most popular one as well known generally. Near Japan, both Pacific plate and Philippine sea plate is going down below continental plate slowly.These plates are carried by mantle convection under them.The going down plates are pulling down continental plate also. But, if the stress becomes over than friction force between these plates, the continental plate will spring back. In the case of the spring back with long time deflection all at once, the huge earthquake should be occurred. On the other hand, if the spring back goes slowly, only small earthquake should be occurred. The phenomenon called as "Slow Slip" is such one. 

Before huge earthquake, micro earthquakes with Slow slip had often been occurred as the sign of huge one. It seems to be similar that the full drawing bow must be allowed only micro moving. As I wrote in Image of Earthquake as cracking phenomenon (2) , there are many data of Details Unknown" with unknown depth in database of Japan Meteorological Agency (JMA). I guessed the reason why the depth are unknown that too shallow epicenters might be not enough to calculate the depths from the time lags between S-wave and P-wave. But, I wonder if some of them might be Slow Slip because of the slow process.