I would have to think that was more than a 6.3 quake.
The shallowness has been the reason given for such devastation.
I’s confident even those drooling in cups got the point.
The quake was right under the city and the city is built on sand, gravel and dirt with a water table below it. Liquification is a fact there. The shaking that the city felt would have been tremendous, more than just the Richter Scale would suggest. There are other scales which quantify the severity in terms of the shaking felt and damage done. Those scales will better reflect what Christchurch is experiencing.