Great
Earthquakes In Diverse Places
New Zealand: Strong Earthquake shakes a large part of the
central South Island
PAUL GORMAN
Last updated 05:00 02/05/2011
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.