The “Kaiapoi” Fault – What’s the Story?

I went to the GNS Science briefing yesterday to hear about the latest flurry of aftershocks.  And yes, the 5.2 at 1.21 a.m. this morning did wake me up.

The “Kaiapoi” Fault is the new name for the one they’ve discovered under the sea off the Waimakariri mouth.  It does not pass underneath Kaiapoi.

Most of the recent aftershocks have been out to sea and although they are trending north-east, they aren’t affecting this fault.  The seismologists told us that the Kaiapoi Fault has been active periodically in geological time which means that there has been a progressive release of stress along it.  That should be good news for us in North Canterbury because that release of stress means that it is less likely to be a big one if the fault ruptures.

We are likely to continue to get aftershocks in this part of Canterbury for many years, although as time goes on they will become imperceptible.  Aftershocks from the 1968 Inangahua quake are still going on.

The aftershocks experienced in the Oxford area after the September earthquake were not unexpected.  Apparently the Mount Oxford area is quite seismologically active and, once again, the periodic release of stress is a good thing.

None of this, of course, takes away the very real threat to the region of the Alpine Fault, which is on the boundary of the Pacific and Australian tectonic plates.

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