The Ghost of L’Aquila Quake

Satellite image of Earth movement during Italy quake

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.

The technique is 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 millimeters – can be made of any ground motion taking place between image acquisitions.

Each rainbow band represents about 28 millimeters of ground movements. Credits: INGV. Caption: ESA.