The 2013 Seddon earthquake measured 6.5 on the moment magnitude scale and was centred in New Zealand's Cook Strait, around 20 kilometres (12 mi) east of the town of Seddon in Marlborough. The earthquake struck at 5:09:30 pm on 21 July 2013 (05:09 UTC) at a depth of 17 kilometres (11 mi), according to Geonet. The United States Geological Survey also measured the quake at 6.5, at an even shallower depth of 14 kilometres (8.7 mi). The quake caused moderate damage in the wider Marlborough area and Wellington, the nation's capital city 55 kilometres (34 mi) north of the epicentre. Only minor injuries were reported. Several aftershocks occurred during 21–29 July.
The Wellington Region emergency management office was activated on the evening of 21 July, as were those in the lower part of the North Island. On 22 July parts of Wellington's central business district were closed to the public to allow for inspections to buildings with damaged and potentially dangerous façades.
Four people were injured in the quake, which lasted for 20 seconds, blowing out windows, cracking concrete and swaying buildings.