Second Quake In A Week Rocks Seddon

Second Aftershock Rocks Marlborough Region

Mb 3.7, 10km south-east of Seddon, South Island, New Zealand

The Mb 3.7 Seddon Earthquake, visible just right of 80 minutes before timestamp

A magnitude 3.7 earthquake has struck just south-east of the township of Seddon in the Marlborough Province, South Island, New Zealand. The earthquake had a focal depth of 19 kilometres and struck at 5:15 NZST. Felt reports have been received from Renwick in the west, Ward in the east and Mount Cook, Wellington in the north. The maximum felt intensity was MM4 (light shaking), most probably because of the hour and the focal depth being reasonably deep.

This is the second moderate Seddon aftershock in the past week, with a magnitude 3.7 striking on the 30th October to the north-east of Seddon. Whereas last Thursday's quake had its epicentre on the Awatere River, today's quake occurred underneath Lake Grassmere, where last August's Mw 6.6 mainshock occurred. This is an expected aftershock on what is possibly a northern extension of the Clarence Fault near Cook Strait; looking at Wednesday's aftershock it is plausible that may have occurred on a northern extension of the Awatere Fault, therefore meaning these two moderate aftershock have occurred on two of the main fault lines of the Marlborough Fault System.

It is not unusual for such sizable aftershocks to occur over a year after a sequence's mainshock, although it is relatively unusual for them to be temporally quite close. I still do not believe there is any cause for alarm, especially as both aftershocks have occurred within the general aftershock zone from last July's & August's quakes. Nevertheless the residents of Marlborough must be vigilant as last summer's quakes are likely to have increased the rupturing of more faults in the region in magnitude 5 or higher events.

This article was written on the 3rd October 2014 by J H Gurney