Christchurch Takes A Hit - Again!

I got good news, and I got bad news.

The good news is that Andrew is passing through Sacramento this weekend.

The bad news? Here it is. Andrew reports:

Yikes – shaky day back in Chch today:

Christchurch has been hit by its largest earthquake in recent weeks this afternoon, with a 5.2-magnitude shake sparking the evacuation of 1000 workers from the Red Zone.

The earthquake struck at 2.44pm at a depth of 11 kilometres and was centred 10km east of Christchurch, according to the GeoNet website.

...There have been some reports of people running from malls in Christchurch and New Brighton Library has been evacuated to check for damage, while Orion said its systems show

...The central city red zone cordon has been evacuated, with up to 1000 rebuild workers and demolition contractors told to leave the danger zone.

Debris was reported falling from already quake-damaged buildings and more bricks reportedly came down off the crippled Christ Church Cathedral.

Cantabrians turned to social media to report their experiences on the latest shake - the 31st biggest since the earthquake sequence began in September 2010. Today's quake was the first jolt above magnitude 5.0 since January 15.

I replied:

Cripes! I was checking just yesterday, and noted the 4.8 on Saturday, and the guarded optimism in articles written in February that things were quieting down. The epicenter is about the same place as in December: the blind thrust faults to the east. I'm half-expecting the movement to shift north, but no such sign as yet. Maybe things WILL quiet down soon - just not now.

Andrew replied:

Statistically speaking (which isn’t necessarily the best way to view things), there has been a large quake once every 4-6 months or so.

Sept 4 was the first one (7.4 magnitude) Feb 22 was the devastating one that killed hundreds of people (6.3) June 13 (6.0 or thereabouts) December 26 (6.0 or thereabouts).

So I was half expecting something by late June and I hope this was it and that this isn’t a precursor to another in the 6.X scale.

The good thing is that the trend is downwards in the magnitudes of the largest ones I think.

I replied:

It's funny about that quasi-periodicity: I've been half-expecting a new quake too, and I'm sure we're not alone.

The nature of the faults is much different around Darfield (slip) than it is east of Christchurch (thrust). Beginning vs ending (I hope). Unless the faults to the north become active. (cross fingers).

Andrew replied:

And do you have any information or opinion on the >10,000 aftershocks? Is that normal for earthquakes? Seems like a lot to me.....(but I am not an expert in that field of course).

I replied:

No opinion or knowledge about the number of aftershocks, but it is interesting how shallow most of them are. It's all strong but brittle rock that's shattering like a porcelain plate. When I next visit, I want to take a day & hike the Port Hills, just to check out the china. Possibly dangerous hike too. People were killed up there, if I recall.

In any event, this Web Site is important to keep abreast of the quakes.