Wild Land

A moderately strong earthquake struck Cook Strait last evening. The noisy quake was felt strongly in Marlborough and the Wellington region.

Sunday 4th December, 2011

A magnitude 5.7 earthquake struck beneath Cook Strait at 7:19 last evening. The quake, at a depth of 60 km, was centred 30 km east of Picton, 40 km west of Wellington, according to GeoNet.

The U.S. Geological Survey reports the event as magnitude 5.3, centred 30 km south-south-west of Wellington at a depth of 59 km.

[click for larger image] The earthquake left a strong trace on GeoNet’s seismograph network, with shaking felt from Rotorua to Oamaru.

[click for larger image] GeoNet’s shaking map shows that MMVI shaking was experienced in much of the Wellington region and at Picton, Seddon and Nelson in the South Island. MMVI shaking is defined as slightly damaging and is described as follows: “Felt by all. People and animals are alarmed, and many run outside. Walking steadily is difficult. Furniture and appliances may move on smooth surfaces, and objects fall from walls and shelves. Glassware and crockery break. Slight non-structural damage to buildings may occur.”

More than 4,000 reports of the earthquake have been filed by the public, with minor damage reported at Aro Valley, Churton Park, Crofton Downs, Island Bay, Lower Hutt, Lyall Bay, Mount Cook, Newtown, Ngaio, Northland (Wellington suburb), Picton, Porirua, Stokes Valley, Te Aro, Thorndon, Wellington city, Whitby, and Wilton.

A search of GeoNet’s database for earthquakes since 1960, shows that this area of Cook Strait has experienced three other magnitude 5 events in recent times. A magnitude 5.2 quake struck in January 1995 (65 km deep), a magnitude 5.4 event was recorded in March 2000 (47 km deep), and a magnitude 5.1 earthquake in December 2000 (42 km deep). Last night’s quake was the largest and deepest of the four earthquakes.

Since 1960, three earthquakes of sixth magnitude have struck the Cook Strait, Marlborough and Sounds area. On the 18th of January 1977 a shallow magnitude 6.0 earthquake struck beneath Cook Strait near Cape Campbell. A magnitude 6.8 quake on the 27th of May 1992 was centred onshore beneath Marlborough at a depth of 80 km. In 1995, a deep magnitude 6.4 earthquake was recorded near Cape Jackson on March 22nd.

In 1966, a damaging earthquake struck off the coast near Seddon on the 23rd of April. The quake was measured at magnitude 6.1 in offical reports at the time, but is now recorded as magnitude 5.8 in GeoNet’s database.

[Compiled from data provided by the GeoNet project and its sponsors EQC, GNS Science and FRST; and the US Geological Survey and its contributing agencies.]

This entry was posted on Sunday, December 4th, 2011 at 5:09 pm and is filed under Earthquakes - Observations. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.