7 March 2011
Mapping damaged buildings…
At midday on 22 February, a few hours after the tremor hit New Zealand, the International Charter on Space and Natural Disasters was activated by the French civil protection agency and then by the United States for New Zealand’s civil protection teams,” explains Claire Tinel, Project Leader for charter activation at CNES.
Claire Tinel subsequently asked charter member agencies1 to task their satellites immediately to cover the disaster area. Their mission: to obtain high- and very-high-resolution imagery of the centre of Christchurch in order to map the damage inflicted by the quake.
22 February was very cloudy, so we had to wait until the next day for the WorldView-2 and GeoEye-1 satellites to acquire useable images at a resolution of 50 cm,” says Claire Tinel. “Photointerpreters at SERTIT2 then generated a map in less than 6 hrs clearly highlighting collapsed buildings.”
The 6.3-magnitude earthquake seemed mostly to have affected large structures and old buildings in the city centre. This is where emergency teams concentrated their initial efforts to rescue some 50 people trapped under the rubble.
…and ground displacement
But the relief effort was only just getting underway. On 25 February, French scientific teams3 obtained radar images from the Japanese ALOS satellite and worked through the night to produce an interferogram, a map highlighting ground displacements caused by the earthquake.
New Zealand lies astride a region of the globe where the Pacific and Australian tectonic plates meet, so many faults run through it. One of these faults is under the city of Christchurch, generating ground displacements every time there is an earthquake.
“We have received very positive feedback from New Zealand civil protection teams and seismologists about the interferogram,” reports Claire Tinel. “It will allow them to visualize ground displacements adjacent to the fault and to determine their direction—whether the ground moved eastwards or northwards, and whether it lifted or subsided—to help mitigate the effects of any aftershocks.”
A previous earthquake occurred in this region as recently as September 2010, but there were no victims on that occasion. It is now highly likely that New Zealand will experience more aftershocks in the coming months.
1 ESA, CNES, CSA (Canada), NOAA/USGS (USA), ISRO (India), CONAE (Argentina), JAXA (Japan), BNSC /DMC (United Kingdom) and CNSA (China).
2 Service Régional de Traitement d'Image et de Télédétection (regional image processing and remote sensing department, Strasbourg University).
3 Bureau de Recherches Géologiques et Minières (BRGM), Institut de Physique du Globe de Paris (lPGP) and GNS Science (New Zealand).