the most recent chch was only bad cause it was shallow ~5km + very close to the city ~10km (chch is built on crap land also) i.e. bad luck
eg
the christchurch 6.3 @ 10km distance + 5km deep quake was far worse damage than the
chch quake 7.1 @ 40km distance + 5km deep of 6months ago, mainly cause damage falls off by the square of the distance (I assume, ignoring geological features), like sound
the japan quake 8.9 was ~200km away + 10km deep from the nuclear reactors.
If the 8.9 quake happened near tokyo or something I have no doubt deaths would be in the millions as it would be 10,000 times stronger than what it experienced this time
looking at this map it looks like ~200km distance is about 2.5 mag less.
thus the reactors failed at only a magnitude 6.5 earthquake (which is pretty worrying)