Jarrod Booker: Guessing size of quake now a game

Cashel Mall in Christchurch. Photo / Simon Baker

Another strong earthquake. Another chance to play Christchurch's favourite new guessing game.

In thousands of homes and workplaces across quake-battered Christchurch, people initially brace themselves for a few seconds as the quake rumbles through.

"Whoa, it's a biggie," comes the cry in my office. The quake that strikes at 2.44pm yesterday is the strongest since January.

Once the powerful rolling motion subsides, the call is "how big?" and the picks begin to fly.

It's got to be bigger than a magnitude 5 is the quick consensus among the folk in the office. One of the more experienced workers picks 5.2. A few minutes later, as people in mass tap into the quake reporting websites, he's proven exactly right.

His prize is a jug of beer at the pub after work. "I have to buy it myself," he says.

In a Christchurch courtroom, a jury deliberating an important case even asked a court staffer to let them know the magnitude to compare to their own estimations.

Twenty months after the first big quake struck this city, the game is one way quake-hardened residents deal with the barrage.

Despite the unnerving nature of yesterday's quake, most people were able to return quickly to their daily routines. Up to 1000 workers and demolition contractors were forced to leave the cordoned-off central Christchurch red zone as more debris fell from already-damaged buildings, including the doomed Christ Church Cathedral. New Brighton Library was also temporarily evacuated.

Some people fled malls in the city, but emergency services reported no increase in calls. There were reports of minor liquefaction in eastern Christchurch.

The quake, which was 10km deep and centred 20km east of Christchurch, is no surprise, says GNS Science duty seismologist Caroline Holden. The last GNS Science estimates put the chance of a 5.0 to 5.4 magnitude quake in the year to March 13, 2013, at 77 per cent. More about this size could be expected, she said.

The good news was that the trend for the quakes to be moving offshore, away from Christchurch, was continuing.