To be fair, the quake that just hit Tokyo was incredibly deep and lasted a very long time. While as a rule of thumb, a strong quake is followed by only weak aftershocks, in recent history a few strong quakes have actually triggered much stronger quakes sometimes hours later.
@John_Scotus Looking at the location of the 6.1, if it *is* a foreshock then it's the foreshock to the much-feared Nankai Trough megaquake? But, of course, that's an if. One that leaves some really interesting questions about risk and risk psychology to me? "There's a small quantifiable chance of a historic disaster in the near but unknown future" is a wild thing to think about!