Friday, October 3, 2014

Earthquakes - Where the biggest is not the best ...

I was asked the other day if i knew the worlds largest earthquake, it turned out i didn't as i thought it was the 1964 Alaska quake (i wasn't far off though). So i thought i would take a look at the largest quakes in the world, i settled for the top five. And to compare, the top 5 quakes in NZ.

The top five quakes in the world (since 1900)

1 - 1960, Chile. The largest recorded earthquake in the world, a magnitude 9.5 with thousands of people killed, injured and millions left homeless. Large tsunamis were generated and reached up to 10m in Hawaii.

2 -1964, Alaska. The 'Great Alaska Quake' was a magnitude 9.2 and generated a tsunami with a maximum wave height of 67 meters in the shallow Valdez Inlet. The tsunami caused 122 of the 131 deaths of the quake.

The location of the top 5 quakes in the world
3 - 2004, Northern Sumatra. The Banda-Aceh earthquake was magnitude 9.1 this and the 'Boxing Day Tsunami' caused the deaths of over 200,000 people and displaced millions over 14 countries

4 - 2011, Japan. The magnitude 9.0 Tohoku Earthquake and subsequent tsunami killed thousands of people. The tsunami waves traveled 10km inland and reached heights of 39m.

5 - 1952, Kamchatka, Russia. The magnitude 9.0 earthquake also caused a tsunami, with wave heights of up to 15m causing considerable loss of life and damage.

The Top Five in New Zealand

Although magnitude is our common gauge of earthquake size, intensity is a better indicator of how the quake was felt on the surface. The Modified Mercalli Intensity Scale, or MM, ranges from MM1 (unnoticeable) right up to MM12 (completely devastating). To make it easier we have these intensities on the earthquakes posted on GeoNet as words: weak, light, moderate, strong, severe. 

The location of the top 5 NZ quakes
1 - Our largest earthquake was in 1855, the magnitude 8.2-8.3 Wairarapa quake had an intensity of  MM10 and killed 7-9 people. It was also highly destructive in Wellington and generated a tsunami in Cook Strait and Wellington Harbour. It resulted in extensive uplift, including what is now the Hutt Road alongside Wellington Harbour and the Basin Reserve (which was originally part of a waterway that led into the harbour and was proposed as a shipping basin until the quake!)

A damaged road after the Hawkes Bay Quake
2 - 2009, Dusky Sound (Fiordland) magnitude 7.8, MM7.  Due to its isolated location only a few properties were damaged, though it did generate a small tsunami.

3 - 1931, Hawkes Bay,  Also magnitude 7.8, but with an intensity of MM10, this quake is New Zealand's most devastating quake. 256 were killed, thousands injured and it altered the landscape forever. It was followed by uncontrollable fires due to broken water mains, and  is recorded as having caused the largest loss of life in New Zealand’s history.

4 - 1929, Buller. Another MM10, this magnitude 7.8 quake killed 15 people, severely damaged many roads, buildings, and bridges. The massive rumbling of this quake was heard as far away as New Plymouth. It also created thirty-eight new lakes from blocked rivers and waterways. 21 still exist today.  

Ground rupture following the Buller quake
5 - 1934, Horoeka (Pahiatua). Magnitude 7.6. This event caused widespread damage especially in Pahiatua where a number of buildings collapsed.

Although not up there in size, the magnitude 6.3 Christchurch earthquake in 2011 had a MM9, and is our second most devastating quake with 185 deaths. This quake was so damaging due to its shallow (5km) depth and location within 10km of the city.

You can read more information on these, and other historic events here

It is estimated that there are 500,000 detectable earthquakes in the world each year. 100,000 of those can be felt, and 100 of them cause damage (USGS)

Info Sources:

USGS - United States Geological Survey
GA - GeoScience Australia 
Te Ara - The Encyclopedia of New Zealand


  1. One quake is missing from the list although not located in mainland New Zealand it was still within Geo Net's monitoring area: 24 December 2004 Auckland Island 8.1

  2. Yes Paul! The second, with a magnitude of 8.1 and so classed as a great earthquake, occurred on December 24 and was centred 430 km west of the Auckland Islands and over 700 km south-west of Stewart Island. This was at a depth of 10 km, and was felt widely in the South Island and at a few places in the North Island. At the time of occurrence, this was the largest earthquake that had occurred worldwide for over a year, subsequently surpassed by the devastating Indian Ocean event on Boxing Day.

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