Saturday morning’s significant earthquake might have provided something out of the ordinary for scientists to study.
The magnitude-5.2 quake at 7.08am shook a large part of the central South Island, but was centred well away from where most aftershocks have been following the big quakes on September 4 last year and February 22.
The epicentre of the 9km-deep shake was in the ranges between the Waimakariri River and Lees Valley, about 20km northwest of Oxford. By last night, the GeoNet website had received more than 810 “felt” reports from across Canterbury and the West Coast, and as far away as Nelson and Dunedin.
Many of the aftershocks in the past eight months have been near the ends of the Greendale Fault and along the length of the Port Hills Fault.
There have also been aftershocks centred closer to Oxford, but Saturday’s was beyond the town and over the other, northern, side of Mt Oxford, near the Townshend River.
Canterbury University retired geologist Jocelyn Campbell said the area from Porters Pass through to Lees Valley was very seismically active, with a “spaghetti junction” of faults running through the Canterbury foothills and across North Canterbury.
Two thousand to three thousand years ago, a very large earthquake, possibly up to magnitude eight, had been generated by a fault in Lees Valley that left a visible eight-metre rupture.
Saturday’s quake in about the same area could well have been on a strand of the Porters Pass Fault or one linked with it, Campbell said.
It was felt strongly in the Oxford, Springfield and Loburn areas.
Three 10km-deep quakes near Governors Bay within two minutes early yesterday were felt in parts of Christchurch. The largest, at 1.19am, was of magnitude 3.6. Another magnitude-3.3 aftershock, 7km deep, was recorded at 11.42am between Lyttelton and Redcliffs.
PAUL GORMAN © 2011 Fairfax New Zealand Limited