Thought I would start a new thread as part of my post on Christchurch below was inappropriate, before I knew the quake was deadly (although I should have expected it would be deadly). The link below is to a news article. I checked the population of Christchurch and it is larger than I thought: almost 400,000. Wikipedia is very fast; there is already a brief mention of this quake. The linked article says USGS says that it is part of the aftershock sequence of the Sept 2010 M7.1. I think that depends on how you define aftershock sequence. I don't think this quake was on the part of a fault that broke in September. It may not have even been on the same fault. But, when those who do them do a static stress change map, I imagine that the fault where yesterday's quake occurred was brought closer to failure (we shall see; I may search).

The historical seismicity on the USGS page does not seem to show what must be a solid line of aftershocks to the Sept 2010 quake, so I am pretty sure it is not updated. I looked because I wanted to see how close the Sept quake ruptured to Christchurch.

The news story on the ABC morning show today said the damage was far worse by this quake because it was shallower. This is not true: the other quake, I'm pretty sure, broke the surface. The problem is that the M6.3 was within Christchurch while the other was somewhat distant.

While the following comment is not helpful to what New Zealand has to deal with now. But, I would be curious to see a map showing the rupture length of this quake and the Sept 2010 quake, as well as any mapping of the fault that broke in September. Is there an unbroken part of the September fault that extends towards Christchurch, or did the 6.3 rupture it? Or is the 6.3 on a different fault?

Chris

• CNN article Christchurch earthquake