August 19, 2019

NZ Christchurch earthquake mapped from space

Alos Earth Observation Satellite - my what large solar panels you have.

Last months devastating earthquake in Christchurch, New Zealand has been mapped from space using new radar imagery.

The shallow magnitude 6.3 tremor killed over 200 people and shattered a modern city just geting back on its feet after a 7.1 earthquake in September 2010.

Data gathered by the Japanese Alos spacecraft has been used to map the way the ground deformed during the 22 February earthquake.

It shows that the tremor was centred right under the city’s south-eastern suburbs.

The type of imagery used to display the movement of the land towards and away from the spacecraft is known as – brace yourselves – a synthetic aperture radar inteferogram.

‘Inteferogram’ sounds like something governments might do.

The aperture radar inteferogram image is made by combining a sequence of radar images acquired by an orbiting satellite “before” and “after” a quake.

It allows precise measurements to be made of any ground motion that takes place between the image acquisitions snapshots.

The coloured bands, or fringes, represent movement towards or away from the spacecraft. The imagery does not work with water, so the bright colouring over the Pacific Ocean east of Christchurch is just the waves making colourful patterns on the inteferogram.

In the inteferogram of the Christchurch quake, 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, United Kingdom.

“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.”

Scientists are studying the Alos information to understand better the future seismic hazards in this part of New Zealand.

It has become obvious from recent events that Christchurch sits close to “blind faulting” – faulting that is at risk of rupture, but which betrays little evidence of its existence at the surface, meaning the potential danger it poses is not properly recognised.

Christchurch is not an area of New Zealand where there has been significant seismic in the past, hence the large number brick and stone buildings constructed since European settlement began 150 years ago.

The Japanese Alos Earth Observation Satellite was launched in 2006. At the time it was Japan’s largest, with 72 foot solar panels.

Anatomy of an earthquake as seen by Alos Spacecraft.