Earthquakes Near Hanmer

32 earthquakes have been recorded about 40 km north of Hanmer Springs in the South Island since the magnitude 5.6 quake of October 4th.

A magnitude 4.7 earthquake struck 40 km north of Hanmer Springs at 1:52 this morning, Sunday 7th October 2007. The 70 km deep quake was the second largest quake in a series of 33 which have struck within a radius of 10 km of a point half-way between Hanmer Springs and St Arnaud including the magnitude 5.6 quake of Thursday morning.

Most of the quakes (29) have occurred at depths of 44-70 km, with a further 4 at greater depths. The series of quakes looks to be a typical main shock followed by a series of aftershocks, with this morning’s quake following the rule of thumb that the largest aftershock is usually about one order of magnitude lower than the main event. The series has included one event of 5th magnitude, two of 4th magnitude, thirteen of 3rd magnitude, fifteen of 2nd magnitude and two of 1st magnitude according to data in GeoNet’s database.

Only two of the quakes have been reported felt by the public, the magnitude 5.6 quake attracting 2157 reports to date, and this morning’s magnitude 4.7 tremor attracting 52 reports from as far away as Akaroa on Banks Peninsula, Runanga and Birchfield on the West Coast, Motueka and Wellington.

The town of Hanmer Springs is, of course, well-known for its hot springs. Unlike Rotorua, where the hot springs and geysers are fueled by volcanic processes, the waters of Hanmer’s springs gain their warmth from rock heated by tectonic compression as the Pacific and Australian plates press against each other.

The area directly above the earthquakes, which are in the subducting Pacific Plate, is on or near the Awatere earthquake fault, one of three large faults which cross the complex tectonic transformation zone. Within this zone, the interacting plates change from sliding under movement to sliding-past movement along the Alpine Fault.

[Compiled from data provided by the Geonet project and its sponsors EQC, GNS Science and FRST.]

Leave a Reply