A 6.3-magnitude earthquake shook the New Zealand city of Christchurch on Monday. It was preceded about an hour earlier by a 5.6-magnitude foreshock.
The tremors are aftershocks from the 6.3-magnitude quake that unexpectedly hit the city on 22 February.
This time, several buildings collapsed and power was disrupted. The greatest force of the quake hit areas that were already damaged, however, leaving most of the city centre unaffected.
Advertisement
The recent earthquakes struck only 3 kilometres south of the epicentre of February鈥檚 quake. But , a seismologist at the Institute of Geological and Nuclear Sciences (GNS Science) in Lower Hutt, New Zealand, says they occurred on 鈥渁 completely different fault line鈥�.
Since February, GNS Science has been monitoring aftershocks in the New Zealand region of Canterbury, in which Christchurch lies. These observations revealed a 鈥渄istinct cluster鈥� of aftershocks in the new region, suggesting this is a new fault line, says Fry.
Moving and shaking
鈥淭he ground motions were also quite different in the two events,鈥� he says. Most of the movement in the February quake was caused by the tectonic plates thrusting over each other, but this time, the plates were moving 鈥渇rom side to side鈥�. At their fastest the plates accelerated at 20 metres per second2.
According to Fry this fault line was activated by February鈥檚 quake, which triggered a lot of movement in the plates.
, a seismologist at Victoria University of Wellington, New Zealand, says the recent quake could 鈥渞e-energise the system鈥� and create a new wave of aftershocks in the region. Christchurch has been trembling since February, with minor quakes , but this is the largest aftershock yet recorded.
