Monday, July 20, 2009

Earthquake in New Zealand

Monday, July 20, 2009
after some research I am beginning to wonder why I am living here - seems there is a reason why we are called the "shaky Isles" as we have many earthquakes in New Zealand - some are not so big - in fact the bulk of them you cannot feel. It's the ones you can feel that we are worried about.
Anyhow - below is a list of the most significant earthquakes from the last 150 years or so!
Scary thing is - the main Alpine fault line is due to rupture and when it does it will be in excess of 7.9 - meaning there will be widespread damage in Christchurch !! Me makes mental note - the best place to be at the next earthquake is in a helicopter - at 500 feet above ground!!!!!!

The Alpine Fault

NZ main alpine fault line from spaceThe western ramparts of New Zealand’s Southern Alps define a remarkable straight line visible from space – the trace of the Alpine Fault. It is the longest active fault in New Zealand. Onshore it extends 650 kilometres from Blenheim to Milford Sound.

The Alpine Fault is a major plate boundary, where the moving Pacific and Australian plates collide and scrape past each other. In 1948 geologist Harold Wellman realised that rocks that were once adjacent to each other had been separated by 480 kilometres as a result of movement along the Alpine Fault.

No major earthquakes have occurred on the Alpine Fault since Europeans settled in New Zealand. Its most recent movements have been determined by tree-ring dating and radiocarbon dating of plant material in trenches dug across the fault. Dates from earthquake-triggered landslides and forest disturbance indicate an earthquake around 1460 AD. Another quake occurred about 1630, when there was movement along the fault between the Paringa and Ahaura rivers (about 250 kilometres). The most recent earthquake was about 1717, when over 300 kilometres of the fault ruptured, from Milford to the Haupiri River.

On these occasions there was up to 8 metres of horizontal movement and 1 to 2 metres of uplift along the fault, producing earthquakes with magnitudes of about 8.

Major ruptures

Over the last thousand years, there have been four major ruptures along the Alpine Fault causing earthquakes of about magnitude 8. These occurred in approximately 1100, 1450, 1620 and 1717 AD, at intervals between 100 and 350 years. The 1717 quake appears to have involved a rupture along nearly 400km of the southern two thirds of the fault. Scientists say that a similar earthquake could happen at any time as the interval since 1717 is longer than between any of the earlier events.

New Zealand main alpine faut line

Here is a landsat pic from space - and the clearly visible main alpine fault line running from north to south - with Fjordland to the bottom left hand side.

Recent shakes - note the two 6.something shakes did some major damage to the towns as did the Hawkes Bay shake - it flattened the town!

October 10, 1848
October 19, 1868
Cape Farewell
January 23, 1855
September 1, 1888
North Canterbury
March 9, 1929
Arthurs Pass
June 17, 1929
February 3, 1931
Hawkes Bay <------
March 5, 1934
June 24, 1942
August 2, 1942
May 24, 1968
March 2, 1987
Edgecumbe <-------
August 22, 2003
December 20, 2007
Gisborne <--------
July 15, 2009

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