Christchurch quake mapped from space


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The upheaval wrought by the 22 February earthquake in Christchurch, NZ, is illustrated in new radar imagery.

The Magnitude 6.3 tremor killed more than 160 people and shattered a city already reeling from a previous seismic event in September.

Data from the Japanese Alos spacecraft has been used to map the way the ground deformed during the most recent quake.

It shows clearly that the focus of the tremor was right under the city's south-eastern suburbs.

The type of image displayed on this page is known as a synthetic aperture radar interferogram.

It is made by combining a sequence of radar images acquired by an orbiting satellite "before" and "after" a quake.

The technique allows very precise measurements to be made of any ground motion that takes place between the image acquisitions.

The coloured bands, or fringes, represent movement towards or away from the spacecraft.

In this interferogram, the peak ground motion is almost 50cm of motion towards the satellite.

"It's like a contour map but it's showing to the south-east of Christchurch that the ground motion is towards Alos. That's uplift," explained Dr John Elliott from the Centre for the Observation and Modelling of Earthquakes and Tectonics (Comet) at Oxford University, UK.

"And then right under Christchurch, we see subsidence. That's partly due to liquefaction but it's mainly due to the way the Earth deforms when you snap it like an elastic band."

Where the rainbow fringes become most tightly spaced is where the fault break came closest to the surface, although the data indicates the fault is unlikely to have broken right through to the surface.

http://www.bbc.co.uk/news/science-environment-12668190 (images at the site)

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thats very interesting, i never knew that an earthquake can reshape the earth like that.... shame that they couldnt do the mapping for more of the areas, tho

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