City quake-free for eight days
Christchurch Earthquake 2011
It is a statistic some will not like for fear of tempting fate, but it's a fact - Christchurch has now gone more than a week without a ''felt'' earthquake.
Several quake websites, including that of GNS Science, show the city and wider region are enjoying a quiet time, seismologically speaking.
In fact, it is the quietest it has been since September 3, 2010.
Until this morning, the last quake that generated ''felt'' reports to GeoNet was a 10-kilometre-deep, magnitude-3.2 jolt at 10.19am on Sunday, August 19. Even that was reported as ''felt'' by just a handful of people.
The last more widely felt quake across the city was an 8km-deep, magnitude-3.7 tremor on Thursday, August 9, at 8.03pm.
Since the quake sequence began on September 4 nearly two years ago there have been periods of two or three days without felt seismic activity, but never an eight-day stretch.
GNS Science duty seismologist Caroline Holden said it was not all that calm when smaller quakes were taken into account.
''We haven't had any felt ones, but there's still been quite a few magnitude 2s, but they happen to be a bit offshore so are not felt. On average, it hasn't been exceptionally quiet,'' she said.
It was ''incredible'' that aftershocks were still occurring almost two years after the magnitude-7.1 quake.
''It hasn't really stopped in all that time,'' she said. ''It has been a rich [aftershock sequence] and the quakes have been so shallow.''
The lack of felt quakes in the past week was in line with the usually expected aftershock decay rate, she said.
GNS Science's latest aftershock probability forecasts for central Canterbury show that in the 12 months to August 9 next year there is a:
❏ 74 per cent probability of a magnitude-5.0 to 5.4 aftershock.
❏ 32 per cent probability of a magnitude-5.5 to 5.9 aftershock.
❏ 10 per cent probability of a magnitude-6.0 to 6.4 aftershock.
❏ 3 per cent probability of a magnitude-6.5 to 6.9 aftershock.
❏ 1 per cent probability, or one in a hundred chance, of a magnitude-7.0 quake or higher.
- © Fairfax NZ News
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