Sep 9 2010 - Porangahau again!
On Tuesday, September 7 at 10:48 am (NZST) a magnitude 5.2 earthquake occurred 20 km south-east of Porangahau. Again on Thursday, September 9 at 4:18 pm (NZST), a magnitude 5.3 earthquake occurred in much the same location.
The first earthquake epicentre was about 15 km deep. It was widely felt from Hastings to Wellington, with the GeoNet website receiving over 815 felt reports to date, two reporting slight damage. The second earthquake was slightly deeper at 20 km. 980 felt reports have been received to date, but with no reports of damage.
These earthquake is not related to the Darfield earthquake and the subsequent aftershock sequence. This earthquake occurred near the interface of the subducting Pacific Plate with the overlying Australian Plate. The mechanism of the first earthquake was strike-slip, the second was reverse faulting.
Rocks in both the subducted Pacific Plate and overlying Australian Plate are very competent in this region. Seismic waves from this earthquake travel to the surface very efficiently with little loss of energy, generating wide ‘felt’ effects for a relatively small event.
Similar types of earthquake commonly occur in the same vicinity, on average one every two years, so it is unusual for two similarly-sized earthquakes to have occurred within two days of each other.
