Satellite images show earth moving quake

Italian scientists have begun to analyse the devastating effects of last month’s earthquake that shook the medieval town of L’Aquila in central Italy.

An Envisat Advanced Synthetic Aperture Radar (ASAR) interferogram over the L’Aquila area in central Italy showing the deformation pattern caused by the seismic events in early April 2009. Credits: IREA-CNR

Studying satellite radar data from ESA’s Envisat and the Italian Space Agency’s COSMO-SkyMed, scientists have begun analysing the movement of Earth during and after the earthquake that struck on 6 April 2009.

The team - from Italy’s Istituto per il Rilevamento Elettromagnetico dell’ Ambiente (IREA-CNR) and the Istituto Nazionale di Geofisica e Vulcanologia (INGV) - are using a technique known as SAR Interferometry (InSAR), in essence a sophisticated version of 'spot the difference'. InSAR involves combining two or more radar images of the same ground location in such a way that very precise measurements – down to a scale of a few millimetres – can be made of any ground motion taking place between image acquisitions.

The technique merges data acquired before and after the earthquake to generate 'interferogram' images that appear as rainbow-coloured interference patterns. A complete set of coloured bands, called ‘fringes’, represents ground movement relative to the spacecraft.

"We produced an interferogram just a few hours after the Envisat acquisition by combining these data with data acquired before the earthquake. We were pleased that we were able to immediately see the pattern of the earthquake," said Riccardo Lanari of IREA-CNR.

The Envisat interferogram shows nine fringes surrounding a maximum displacement area located midway between L’Aquila and Fossa, where the ground moved as much as 25cm (along a line between the satellite’s orbital position and the earthquake area).

"By using available 3D ground displacements from five GPS location sites around the affected area, we were able to confirm the preliminary results obtained with Envisat data," Salvi said.

To ensure all scientists are able to contribute to the analysis of the earthquake, ESA is making its Earth observation dataset collected over the L’Aquila area freely accessible with an innovative fast data download mechanism.