2013 Lake Grassmere earthquake


The 2013 Lake Grassmere earthquake was a magnitude 6.6 earthquake that occurred at 2:31:05 pm on Friday 16 August 2013. The epicentre was located about 10 km south-east of Seddon, under Lake Grassmere, with a focal depth of 8 km. The earthquake caused significant land damage in the local area, with landslips blocking roads, including the main highway between Blenheim and Christchurch. Buildings in Seddon were damaged, with some being declared uninhabitable. The earthquake was widely felt in both the North and South Islands of New Zealand.

Earthquake

This earthquake is considered to be a doublet of a magnitude 6.5 earthquake that occurred in Cook Strait on 21 July 2013 and is thought to have occurred on part of the same complex of faults. It started its own aftershock sequence, with several magnitude 5 and one magnitude 6 earthquakes occurring in the first few hours after the main shock.

Aftershocks

The earthquake generated a significant series of aftershocks, the largest of which had a magnitude of 6.0.
Below is a list of all aftershocks magnitudes 5.0 and above that occurred in the region between 16 August 2013 and 5 September 2013.
Date Time Magnitude Magnitude Magnitude EpicentreDepth
16 August 20132:31:05 pm6.56.06.610 km southeast of Seddon8 km
16 August 20132:37:27 pm5.45.45 km southeast of Seddon9 km
16 August 20132:45:27 pm5.55.15.410 km southeast of Seddon6 km
16 August 20132:56:27 pm4.95.020 km east of Seddon9 km
16 August 20133:09:08 pm5.95.45.510 km south of Seddon8 km
16 August 20133:21:31 pm5.15.010 km south of Seddon17 km
16 August 20133:51:35 pm5.15.25.610 km east of Seddon19 km
16 August 20135:31:16 pm5.95.86.015 km east of Seddon14 km
16 August 20135:56:10 pm5.05 km northwest of Seddon10 km
16 August 20135:57:52 pm4.85.120 km east of Seddon5 km
16 August 20136:42:40 pm5.220 km east of Seddon20 km
16 August 20136:55:58 pm5.05.520 km east of Seddon20 km
16 August 20138:38:54 pm4.74.65.210 km southeast of Seddon22 km
17 August 20134:13:20 pm4.85.015 km southwest of Seddon20 km
17 August 20138:58:39 pm5.25.15.510 km south of Seddon20 km
18 August 20134:07:52 am4.64.45.05 km southeast of Seddon20 km
5 September 201312:04:10 am4.85.135 km northeast of Seddon16 km

Damage

In Wellington, the earthquake caused minor damage to buildings, breaking some display windows and cracking plaster. Many central city office workers left work early, and with all suburban train services cancelled for urgent track inspections, bus services overloaded and traffic gridlock occurred on major roads out of the city for a couple of hours. The City Council ordered the deconstruction of a 30-year-old lift shaft that had been damaged in a previous earthquake in July, after recently installed emergency seismic restraints failed. Several surrounding buildings in the fall zone were ordered to be evacuated.

Seddon

The quake caused substantial damage to a number of residential homes in the Seddon area. Eight houses were evacuated by The Marlborough District Council and another 11 allowed only restricted access.

Rest of NZ

The quake was felt as far north as Auckland and far south as Dunedin. Damage was reported in the Kapiti Coast, Hutt Valley, Wellington, Blenheim, Ward and the rest of West Upper South Island.