Satellites show how Earth moved during Italy quake


Envisat interferogram over the L'Aquila area
 
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. This interferogram was generated by Italy’s Istituto per il Rilevamento Elettromagnetico dell’ Ambiente (IREA-CNR) in Naples, Italy just a few hours after Envisat’s acquisition on 12 April 2009. It combines that acquisition with a pre-seismic acquisition on 1 February 2009, with an estimated baseline (separation between the two Envisat orbital positions) of about 154 m. The satellite’s right-looking angle is 23 degrees. Each fringe of the interferogram, corresponding to a colour cycle, is equivalent to an Earth surface displacement of 2.8 cm along the satellite direction.

Interpreted Envisat interferogram
 
An Envisat Advanced Synthetic Aperture Radar (ASAR) interferogram interpretation by Italy’s Istituto Nazionale di Geofisica e Vulcanologia (INGV). The large green square represents the Mw 6.3 main shock, the smaller green squares represent the Mw > 5 aftershocks and the black triangles represent GPS stations used for SAR validation. The yellow line east of L’Aquila shows the location of a ~4 km–long alignment of co-seismic surface breaks observed in the field by INGV researchers. This alignment corresponds to a northwest - southeast strip where the spatial fringe rate seems to exceed the limit for interferometric correlation. This may indicate that the fault dislocation reached, or was very close to, the surface along this line. The observed pattern of ground displacement is in very good agreement with the earthquake source mechanism (the ‘beach ball’), confirming that the earthquake source is a normal fault striking 144 degrees (clockwise from north), and dipping to the southwest.

A damaged church in L'Aquila
 
This aerial image taken on 8 April 2009 shows a view of a church of the Abruzzo capital L'Aquila, epicentre of a violent earthquake two days earlier.

COSMO-SkyMed interferogram
 
COSMO-SkyMed interferogram using data from 19 February 2009 and 9 April 2009. Perpendicular baseline is 480 m, and the satellite’s right-looking angle is 37 degrees. The large green square represents the Mw 6.3 main shock, smaller green squares represent the Mw > 5 aftershocks, the yellow line marks the observed co-seismic surface breaks and the black triangles represent GPS stations used for SAR validation.



Release date: 28 February 2012