A second earthquake, worse than the first, is more than any city should have to bear. The 6.3 shake that hit Christchurch yesterday was worse in every way but magnitude. It was shallower, closer to the city, buildings that somehow survived the 7.1 quake in September toppled yesterday. But worst of all, it happened in the middle of a working day when people were all around.

The common reaction to September's pre-dawn quake was, "Imagine if it had happened in daytime." Nobody needs to imagine now. In the immediate aftermath, parents tried desperately to contact children at schools, working couples anxiously called each other, families who endured the first shake together in their house were worried for each other this time. With reason. Last night's confirmation of 65 casualties and perhaps many more was sadly inevitable given the evidence of destruction.

New Zealand watched the horror in daylight this time. The familiar television scenes of disaster - buildings reduced to rubble, ambulances racing, fire crews and emergency teams at work, worried onlookers, - were not coming from a distant country, it was happening here. This quake has shaken not only the regions that felt it, but the whole country that witnessed it.

Its destructive power has been worse than the first. Some of Christchurch's grandest historic buildings were reported damaged: the provincial council chambers, the arts centre, the cathedral in the square. The fall of the cathedral spire, the city's symbol, is a blow to the visible heart of Christchurch but that loss will be temporary. The restoration of the spire can become a focus for the city's spirit.

Christchurch sorely needs something to revive its spirit now. It has endured hundreds of aftershocks since September, usually in a spate followed by a lull that is long enough to let the city dare hope the ordeal is over. Boxing Day's shake dashed weeks of hope. Yesterday's was worse.

The land had settled just long enough for residents to begin getting restive at the lack of restoration work in the suburbs worst hit in September and the delay this is causing in the repair or replacement of their homes. Now they probably face a new wait for more liquefaction to settle and the latest damage to be assessed.

There is only so much trauma a community can bear. Christchurch passed that point a long time ago. Yesterday, the people there sounded numb.

A quake more damaging than the first is more worrying because it shakes confidence in science's explanations. Ever since the first, geologists have been reassuring Christchurch the ongoing frequent tremors have been aftershocks that commonly occur after a major seismic release. While these could go on for a year and some could be quite big, none would be as big as the initial shock.

Well, yesterday's was nearly as big. It triggered its own swarm of aftershocks during the day. Its scale makes it hard to suppress the question, is something even bigger building up under Canterbury? This was not a region prone to earthquakes until five months ago.

Geologists have calculated that a "big one" is due somewhere along the Great Alpine Fault in the South Island but they insisted the September quake, centred near Darfield, was too far from the main faultline. Yesterday's quake occurred even further from the alpine fault, near Lyttelton. They remain convinced it is just another consequence of the first shock. May they be right.

But if aftershocks of this magnitude can happen, it is time for some more drastic precautions in Christchurch. People should not be working or shopping in or around buildings that may collapse in a shallow aftershock of this magnitude. A disaster in broad daylight clarifies the continuing risk.