I had missed that the M5.7 after the 6.9 was no where near the 6.9 and its aftershocks. I saw in a news item that there was a quake offshore Tokyo and this is the one. No focal mechanism on USGS site yet. It was followed by a M5.2 well to the east near same latitude.

This area is near south edge of M9 quake so would be an area of some concern.

and, yes, logic would suggest that the 5.7 was triggered even though 5 deg of latitude (550 km) and 4 deg of longitude away (so maybe 700 km? not doing the math).

Chris