Wairarapa earthquake of 1855

from Wikipedia, the free encyclopedia
Wairarapa earthquake of 1855
1855 Wairarapa earthquake (New Zealand)
Bullseye1.svg
Coordinates 41 ° 24 ′ 0 ″  S , 174 ° 30 ′ 0 ″  E Coordinates: 41 ° 24 ′ 0 ″  S , 174 ° 30 ′ 0 ″  E
date January 23, 1855
Time 9:32 p.m. local time
intensity 10  on the MM scale
Magnitude 8.2  M W
depth 25 km
epicenter Palliser Bay
(about 20 km southeast of Wellington)
country New Zealand
Affected places
Tsunami Yes
dead between 7 and 9
Injured 5

The Wairarapa earthquake of 1855 was the most momentous earthquake for Wellington , New Zealand, and is often referred to as the Wellington earthquake due to the proximity of the epicenter and the effects of the earthquake on the city . The earthquake is also said to be the heaviest earthquake in New Zealand history since records began in 1840, despite the fact that the loss of life was far less than that of the Hawke's Bay earthquake of 1931 .

The importance of this earthquake for Wellington is underscored by the fact that from September 8 to 10, 2005, a symposium was held in the Museum of New Zealand Te Papa Tongarewa to mark the 150th anniversary of the event and a detailed consideration of the natural event , also from the point of view of provision for the future.

On January 23, 1855, 15 years after the first settlers reached the port of Petone , an earthquake measuring 8.2 on the Richter scale changed the landscape of the Wairarapa region and the area around Wellington at 9:32 pm .

geography

The location of the epicenter of the quake was given by Grapes & Downes 1997 as 41.4 ° S 174.5 ° E ± 0.5 °; the hypocenter was at a depth of 25 km. It was thus at the most south-westerly point of the Wairarapa Fault , from which the quake may have originated. Other specifications are based on a point near the shore in the northwestern part of Palliser Bay , where the elevation of the terrain was at its highest at over 6 meters.

The breakline of the Wairarapa Fault extended more than 100 km along the southeast flank of the Remutaka Range to a few kilometers north of Masterton . On this line, sloping to the northwest, the ground rose.

Tectonic environment

The Wairarapa Fault and the Wellington Fault a little further to the west, lie in the extension of the Taupo Volcanic Zone , which extends from White Island through the Bay of Plenty , over Rotorua and over the active volcanoes Mount Tongariro , Mount Ngauruhoe and Mount Ruapehu . The two faults on both sides of the Remutaka Range have their southwestern continuation through the Cook Strait to the South Island in the Wairau Fault , the Awatere Fault and the Clarence Fault . Since the North Island lies completely on the Australian plate and the Pacific plate sliding beneath it moves from the so-called Hikurangi trough at about 42 mm per year in a west-southwest direction, the resulting tensions lead to earthquakes and the aforementioned fractures and faults.

Geological and geographical changes

Investigations carried out in 2005 showed that the fractures that formed on the southeastern flank of the Remutaka Range were on average 15 to 18 meters wide and can still be easily detected today, more than 150 years later, in the Wairarapa Valley. According to the trenches, the lateral offset was towards the northwest. Further studies show that the numerous landslides triggered by the quake were most intense on an area of ​​5,000 km² along the fault, but still occurred on over 25,000 km², up to the Whanganui River on the west coast and Cape Kidnappers on the east coast. The changes in the landscape as a result were enormous, but are now difficult to see for laypeople.

The most obvious change in the landscape was the elevation of the ground by 6.4 meters from the fracture zone to the northwest and sloping down to just 0.3 meters on the west coast. The coastline and Wellington Harbor changed due to the shifting of the respective shore zones towards the sea, which reduced the size of the harbor basin accordingly. For example, the shoreline at the jetty at Lambton Quay in Wellington shifted about 300 meters. The former quay is now one of the most desirable and busiest shopping streets in the city. Wellington Airport is now also benefiting from the space gained from parts of Lyall Bay . At Turakirae Head , the southernmost tip and foothills of the Remutaka Range , the former shorelines are still visible. The shoreline from before the earthquake of 1855 is now 4.7 m above today's shoreline. Another 7.1 m higher can be seen another former shoreline, which came from a previous earthquake with raised ground. Above that, two more lines can be made out, 3.7 m and another 3.4 m higher, so that the uppermost recognizable former bank line is a total of almost 19 m above the current bank line. Forecasts assume that the Wairarapa Fault can be expected to cause further earthquakes and elevation of the terrain in the future, although experts consider the changes in the landscape due to the expected landslides to be far more serious.

The quake

Before the shock waves first arrived, those affected claim to have heard a one-minute dull rumble. This was followed by the lifting of the floor with strong vibrations for about 90 seconds. 80% of the chimneys on the houses failed to withstand the shock waves, fell and caused the most damage to the wooden houses. The constructions of the wooden houses withstood the shocks better than those made of stone, an experience that the residents of Wellington and Hutt Valley had already had in the Marlborough earthquake of 1848 , which had destroyed almost all brick houses, which is why they were in the years after preferably use wood as a building material.

Despite the severity of the quake and the already relatively extensive settlement of the area - Wellington had a population of around 3,200 and Hutt Valley around 1,600 - the construction of the buildings also explains the low number of four fatalities. Ironically, the only death in Wellington was a hotel owner who, despite warnings, had his hotel built out of bricks and perished in the rubble of his hotel.

Triggered by the unilateral elevation of the floor, a tsunami occurred in the harbor basin , which first moved in the direction of Lambton Quay . Another tsunami came in from the sea, from the Cook Strait . A height of 7 to 10 m is assumed, with up to 10 meters being reached in Palliser Bay and the streets in the harbor district being up to 2.5 m under water. The tsunamis came in waves, caused by reflections , and lasted for hours in a weakening form.

See also

literature

  • DW Rodgers, TA Little : World's largest coseismic strike-slip offset: The 1855 rupture of the Wairarapa Fault, New Zealand, and implications for displacement / length scaling of continental earthquakes . In: Journal of Geophysical Research . Vol. 111, B12408, 2006 (English).
  • The 1855 Wairarapa Earthquake Symposium - Proceedings Volume . Greater Wellington Regional Council , Wellington 2005, ISBN 0-909016-87-9 (English).
  • All-day field trip to the Wairarapa Fault and 1855 Rupture Sites . Greater Wellington Regional Council , Wellington 2005, ISBN 0-909016-88-7 (English).
  • Nicola McCloy : New Zealand Disasters . Whitcoulls Ltd. , Auckland 2004, ISBN 1-877327-34-4 (English).

Web links

Individual evidence

  1. ↑ M 8.2 - 8.3, Wairarapa, January 23, 1855 . GeoNet - GNS Science , accessed on April 5, 2013 (English).
  2. ^ GL Downes : The 1855 January 23 M8 + Wairarapa Earthquake - What contemporary account tell us about it . Institute of Geological & Nuclear Sciences , Lower Hutt September 2005 (English, symposium).
  3. ^ R. Grapes, G. Downes : The 1855 Wairarapa, New Zealand, earthquake - Analysis of historical data . In: Bulletin of the New Zealand National Society for Earthquake Engineering . Volume 30 , 1997, pp.  271-368 (English).
  4. ^ Wellington / Wairarapa . Earthquake Commission , archived from the original on Aug. 4, 2012 ; Retrieved on March 1, 2010 (English, original website no longer available, link to WaybackMachine from August 4, 2012).
  5. ^ The 1855 Wairarapa Earthquake Symposium - Proceedings Volume . 2005, p.  7 (English).