1855 Wairarapa earthquake

Template: Infobox earthquake / maintenance / property missing

( about 20 km south-east of Wellington )

• Wellington
• Hutt Valley

The Wairarapa earthquake of 1855 was for Wellington in New Zealand, so far most serious earthquake, and is due to the proximity of the epicenter and the impact of the quake often referred to the city as Wellington earthquake. Also, the earthquake is known as the most massive earthquake in the history of New Zealand since records began in 1840, and this despite the loss of life was by far lower than in Hawke's Bay earthquake of 1931.

What was the significance of this earthquake for Wellington and still has, is underlined by the fact that on 8 specially held until September 10, 2005 at the Museum of New Zealand Te Papa Tongarewa a symposium celebrating the 150 limitation period of the event and an in-depth consideration of the natural event, was also carried out from the viewpoint of providing for the future.

On January 23, 1855, 15 years after the first settlers arrived at the port of Petone, altered in the evening at 21:32 clock, an earthquake measuring 8.2 on the Richter scale, the scenery of the Wairarapa region and the area around Wellington.

Geography

The location of the epicenter of the quake was ± 0.5 ° indicated by Grapes & Downes 1997 with 41.4 ° S 174.5 ° E; the hypocenter was at a depth of 25 km. It was thus at the southwestern point of the Wairarapa Fault, from the quake may have originated. Other definitions go from a point close to the shore in the northwestern part of Palliser Bay, where the terrain elevation with over 6 meters was the highest.

The fracture edge of the Wairarapa Fault extended north of Masterton on more than 100 km along the southeastern flank of the Rimutaka Range to a few kilometers. On this line, to the northwest sloping down to the ground lifted.

Tectonic environment

The Wairarapa Fault and the Wellington Fault farther west, are the extension of the Taupo Volcanic Zone, which stretches from White Iceland through the Bay of Plenty, Rotorua and on about the active volcanoes of Mount Tongariro, Mount Ngauruhoe and Mount Ruapehu. The two faults on both sides of the Rimutaka Range its 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 under it shifting shifts from the so-called Hikurangi trough of about 42 mm per year in western southwestern direction, the resulting tensions lead to earthquakes and to the mentioned fractures and dislocations.

Geological and geographical changes

In 2005, the investigations carried out showed that the fractures that originated on the southeast flank of the Rimutaka Range, were on average 15 to 18 meters wide and today, more than 150 years later, in the Wairarapa Valley can be quite readily detected. According to the trenches of the lateral offset was claimed towards the northwest. Further studies that the numerous triggered by the quake landslides of the fault were in an area of ​​5,000 km2 along the most intense, but on more than 25,000 km2, to the Whanganui River on the West Coast and Cape Kidnappers on the east coast, still occurred. The changes in the landscape thus were enormous, are for lay people today but just difficult to see.

The most significant change was the raising of the scenic base by 6.4 meters from the fault zone to the northwest and to the west coast decreasing to only 0.3 meters elevation. Thus, the coastline and the Wellington Harbour altered by the displacement of the respective riparian zones seaward, resulting in the harbor basin reduced accordingly. The shoreline in the amount of jetty on Lambton Quay in Wellington, for example, shifted by about 300 meters. The former Kai is today one of the most sought after and busiest shopping streets in the city. The airport of Wellington is now benefiting also from the gain in area and although parts of the Lyall Bay. On Turakirae Head, the southernmost tip and foothills of the Rimutaka Range, the former shorelines are still visible. The shoreline from before the earthquake of 1855 is now 4.7 m above the present shore line. Another 7.1 m higher another former shoreline can be seen that originated from a previous earthquake ground elevation. In still make out two more lines, 3.7 m and 3.4 m higher again, so that the uppermost recognizable former shoreline is a total of nearly 19 m above the present shore line. Forecasts predict that by the Wairarapa Fault in future quakes are to be expected with terrain increases, which experts consider the respective changes in the landscape by the expected landslide for far more serious.

The quake

Before the first arrival of the shock waves Affected want then have observed a one-minute muffled rumble. Then followed over about 90 seconds, the lifting of the ground under strong vibrations. 80 % of the chimneys on the houses kept the shock waves did not stand and fell down and caused the wooden houses most of the damage. The construction of wooden houses kept the bumps better standing than the stone, an experience that already at Marlborough earthquake of 1848 made ​​the residents of Wellington and Hutt Valley, which had destroyed almost all built of brick houses, which is why they followed in the years preferred to put wood as a building material.

Despite the severity of the quake and the already relatively extensive colonization of the region - Wellington had about 3,200 inhabitants and Hutt Valley about 1,600 inhabitants - can be explained by the construction of the building and the small number of four deaths. The only fatality in Wellington was, ironically, a hotel owner, to build his hotel from bricks which made despite warnings and perished in the rubble of his hotel.

Triggered by the unilateral increase of the soil was in the harbor, a tsunami, the first moving towards Lambton Quay. But from the sea, by the Cook Strait, another tsunami came. It came from a height of 7-10 m, with up to 10 meters have been achieved in the Palliser Bay and the waterfront the streets were up to 2.5 m under water. The tsunami came in waves, caused by reflections, and held for hours in a weakening of the shape.