How Strong was the Christchurch Earthquake?

I had to go to Timaru over the weekend to spend time with my elderly mum. Stopped in at Christchurch on the way, and had time to jump on a bike and pedal around exploring... This is the Merivale Shopping Centre in Papanui Road. Looks quite normal from a distance... But shops on both sides of the road are fenced off. You can see in this Deli window: buns, rolls and other delicacies - laid out exactly as they were on the day of the earthquake. And it's a no-go shop. Behind wire fences. And if you look in the reflection of the window, you can see across the street... Across the street this whole frontage has gone. The bricks have been tidied away now. Cars drive past. So do pedestrians. And the sign insists "We Are Open..." The insides of the shops and office spaces are open to the elements exactly as they were on the day of the earthquake....

These are boxes of shoes all stacked on shelves - many of them - but the whole brick frontage has gone. And next door another office. Open to View. The force of the earthquake was huge. Walls and materials that were massive (dense and weighty), like brick and stone were literally tossed to one side - while the rest of the building (made of wood, lighter and more resilient material) shook back into place. More or less anyway.

I cycled along the avenues until I came more to the Eastern side of the city, by the Avon. The streets were dusty and deserted. Still a lot of dry sand piled in the streets, blowing. Nobody about. Many red-stickered homes. Few cars. Almost expected a tumble-weed to blow down the street. And yet the sun was out and it was a brilliant day. I came along the street because I saw workers up to their eyeballs in sewage repairs. I can't keep away from sewage systems. In the background is a heritage pumping station. The classic brick shithouse. The orange box is a powerful pump. It's taking all the wastewater from a manhole, and pumping it direct into the Avon flowing behind the trees. Residents may be able to flush their loos - and here I could see where it was actully going. The workers were fixing the manhole, and three broken sewer mains. Here's another view of the site. What is interesting is the angle that the pump station is on. It's actually leaning about 10 degrees toward the river....

Here it is close up. Heritage for sure. In one piece. But knocked right off its foundations. You can get an idea of how much the ground has moved and dipped from where the pump station building has ended up. Underneath it is a 20 foot deep sump into which wastewater used to flow, and then was pumped to other trunk sewers, and hence to Bromley wastewater treatment plant. Now, some sewers run uphill. Others are not existant. and others fractured. You really wonder about the wisdom of repairing a system which is at so much risk of liquifaction, and ground movement next time... The NZ Herald headline after the Japan earthquake shouted: "Japan's earthquake 8000 times more powerful than Christchurch". (That's what you get when compare a 6.3 magnitude earthquake with an 8.9 one. Richter scale.) But this simple sum ignores what happens on land. That calculation is energy/hectare. And that comes down to ground acceleration. At Fukushima, ground acceleration was .35 gravity. Christchurch CDB it was 1.1 gravity. In Heathcote Valley it got up to 2.1 gravity. In the CBD the Christchurch earthquake was 3 times more powerful and destructive than on land in Japan. This is because the Chch epicentre was 4km from the CBD and 5km deep, whereas in Japan the epicentre was 130km offshore and 32 km deep. No Tsunami in Chch of course.

Further along the road the scale of the ground movement is evident with this damage to the road and verge.

Concrete gutter sections and road seal tossed around and swallowed up in cracks as the ground heaved... cracks carved through the ground....

...and into this adjacent graveyard. A sad sight by the road. Likely to be one of the last parts of the garden city to be fixed. As one person said to me, "they're already dead...."

But it is poignant. This granite memorial has stood proudly here for the best part of a century. You can see the cast iron retaining post that was there to stop the column from moving. But the force of the earthquake - particularly the upward acceleration, followed by rapid downward and sideways acceleration would have literally thrown this column skywards, then pulled the base down, away from the column, which then toppled sideways, and broke into pieces. And then, adding insult to that injury, the ground shook further liquifying the sand beneath, which oozed up around the pieces....

And in this part of the cemetery, you can see the marble pages of a memorial, almost as if the winds of time have turned the whole place into a landscape like a beach. Full of memories. But memories which will be erased and covered by the passage of time. Leaving only sand, rippling in the wind....