2013 Lake Grassmere earthquake

2013 Lake Grassmere earthquake

Date	16 August 2013
Origin time	14:31:05 NZST
Magnitude	6.6 Mw
Depth	8 kilometres (5 mi)
Epicenter	41°44′S 174°09′E / 41.73°S 174.15°ECoordinates: 41°44′S 174°09′E / 41.73°S 174.15°E
Areas affected	New Zealand
Tsunami	None
Casualties	4 people injured[1]

The 2013 Lake Grassmere earthquake^[2] was a magnitude 6.6 earthquake that occurred at 2:31:05  pm (NZST) on Friday 16 August 2013.^[3] 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

USGS Shakemap^[4]

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 an adjacent fault. 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 (NZST)	Time (NZST)	Magnitude (MW)	Magnitude (Mb)	Magnitude (ML)	Epicentre	Depth
16 August 2013	2:31:05 pm	6.5[5]	6.0[5]	6.6[6]	10 km southeast of Seddon	8 km
16 August 2013	2:37:27 pm		5.4[7]	5.4[8]	5 km southeast of Seddon	9 km
16 August 2013	2:45:27 pm	5.5[9]	5.1[9]	5.4[10]	10 km southeast of Seddon	6 km
16 August 2013	2:56:27 pm		4.9[11]	5.0[12]	20 km east of Seddon	9 km
16 August 2013	3:09:08 pm	5.9[13]	5.4[13]	5.5[14]	10 km south of Seddon	8 km
16 August 2013	3:21:31 pm		5.1[15]	5.0[16]	10 km south of Seddon	17 km
16 August 2013	3:51:35 pm	5.1[17]	5.2[17]	5.6[18]	10 km east of Seddon	19 km
16 August 2013	5:31:16 pm	5.9[19]	5.8[19]	6.0[20]	15 km east of Seddon	14 km
16 August 2013	5:56:10 pm			5.0[21]	5 km northwest of Seddon	10 km
16 August 2013	5:57:52 pm		4.8[22]	5.1[23]	20 km east of Seddon	5 km
16 August 2013	6:42:40 pm			5.2[24]	20 km east of Seddon	20 km
16 August 2013	6:55:58 pm		5.0[25]	5.5[26]	20 km east of Seddon	20 km
16 August 2013	8:38:54 pm	4.7[27]	4.6[27]	5.2[28]	10 km southeast of Seddon	22 km
17 August 2013	4:13:20 pm		4.8[29]	5.0[30]	15 km southwest of Seddon	20 km
17 August 2013	8:58:39 pm	5.2[31]	5.1[31]	5.5[32]	10 km south of Seddon	20 km
18 August 2013	4:07:52 am	4.6[33]	4.4[33]	5.0[34]	5 km southeast of Seddon	20 km
5 September 2013	12:04:10 am		4.8[35]	5.1[36]	35 km northeast of Seddon	16 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 up as Auckland and far down as Dunedin. Damage was reported in the Kapiti Coast, Hutt Valley, Wellington, Blenheim, Ward and the rest of West Upper South Island.

References

1. "M 6.6, Lake Grassmere, 16 August 2013 - Earthquake - GeoNet". info.geonet.org.nz. Retrieved 2015-12-11.
2. Fenaughty, Kevin (17 August 2013). "Damaging quake hits the north-east of the South Island". Geonet. GNS Science. Retrieved 17 August 2013.
3. "New Zealand Earthquake Report -- Magnitude 6.6, Friday, August 16, 2013 at 2:31:05 pm (NZST)". GNS Science. Retrieved 17 August 2013.
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22. "M4.8 - 35km ESE of Blenheim, New Zealand". earthquake.usgs.gov. Retrieved 2015-12-11.
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24. "GeoNet - Quakes". www.geonet.org.nz. Retrieved 2015-12-11.
25. "M5.0 - 33km ESE of Blenheim, New Zealand". earthquake.usgs.gov. Retrieved 2015-12-11.
26. "GeoNet - Quakes". www.geonet.org.nz. Retrieved 2015-12-11.
27. "M4.7 - 28km SSE of Blenheim, New Zealand". earthquake.usgs.gov. Retrieved 2015-12-11.
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29. "M4.8 - 29km S of Blenheim, New Zealand". earthquake.usgs.gov. Retrieved 2015-12-11.
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31. "M5.2 - 29km SSE of Blenheim, New Zealand". earthquake.usgs.gov. Retrieved 2015-12-11.
32. "GeoNet - Quakes". www.geonet.org.nz. Retrieved 2015-12-11.
33. "M4.6 - 31km SSE of Blenheim, New Zealand". earthquake.usgs.gov. Retrieved 2015-12-11.
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35. "M4.8 - 34km SW of Brooklyn, New Zealand". earthquake.usgs.gov. Retrieved 2015-12-11.
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