How much longer can this go on? That question will be uppermost in the minds of Canterbury people after another large earthquake on Sunday. They thought they had found the answer to that question. They had not suffered a jolt of such magnitude for two years or more - long enough to think their ground had settled down.

Now they know differently. Seismologists say Sunday's quake is another in the series that started in September 2010 and could continue for decades. The fact Monday is the fifth anniversary of the one that left many in mourning and the Christchurch CBD in ruins underlines how hard it can be for a city to recover.

A visitor to Christchurch these days sees life returning to the CBD. Many new buildings now stand amid the vacant blocks cleared of the remains of previous inner city landmarks. It is a pity that its most widely recognised landmark, the cathedral, is still in a sorry state of indecision, for elsewhere precious features are either under renovation, like the town hall, or replacements are under construction. Where once there was doubt business would move back into the city centre, now it is visibly happening. A new municipal bus interchange in the CBD shows the council's confidence that it will be hub of what planners call the new Christchurch. The "red zone" east of the inner city has been largely cleared of houses and is becoming wide riverside parkland. Some of the roads are still in a rough state but the services beneath are largely functioning again.

Sunday's quake does not appear to be a physical setback on reports so far. No building seems to have suffered, despite the epicentre being just 10km from the CBD and shallow, 15km beneath the seabed off New Brighton. No drains and sewers appear to have ruptured again. The spectacular collapse of a cliff near Sumner shows what a shaking the region took, as does the reappearance of liquefaction in some places. If the damage from the magnitude 5.7 event is as slight as reported so far, it is a credit to modern building standards.

Christchurch has been shaken by a 5.7 magnitude magnitude quake at 1.13pm this afternoon. There have been no reports of serious damage or injuries but a cliff has fallen in Sumner.

The Valentine's Day quake, as it may be remembered there, is a psychological setback. It will be felt particularly hard by those who struggled longest to regain their peace of mind through the thousands of aftershocks that rattled their houses and their nerves from 2010 to 2012. Despite the signs of progress evident to a visitor, it is the frustrations of insurance and the politics of the rebuild that still fester in conversation there. "Cera", the Canterbury Earthquake Recovery Authority, is being wound up without much public goodwill, having spent $2.7 million on public relations in its final year.

The latest shake will not help the mood improve but it carried a lesson for the whole country. Earthquakes on this scale seldom hit an urban centre but it can happen. It happened in Napier last century too. No part of New Zealand is very far from the meeting of two tectonic plates. The crust beneath us is cracked with fault lines that geologists cannot find until they move. When they do, as Canterbury shows, the shocks can go on indefinitely. It is reason for all regions to be prepared.