The National Institute of Geophysics and Volcanology (INGV) - SAR working group of the National Earthquake Center - has reconstructed, in detail, the trend of ground movements to obtain important information for the purposes of evaluating the seismic sequence following the event of the last October 30 (magnitude 6.5) which hit the provinces of Macerata and Perugia. The activity, coordinated by the Department of Civil Protection (DPC), is carried out by INGV and by the Institute for Electromagnetic Sensing of the Environment National Research Council (CNR-IREA of Naples), centers of expertise in the data processing sectors satellite radar data and seismology, with the support of the Italian Space Agency (ASI). Below, two images created by INGV thanks to the use of radar data acquired by the satellites of the Sentinel-1 constellation of the European Copernicus Programme, exploiting the Differential SAR Interferometry technique.
Figure 1:
The figure shows the differential interferogram obtained from radar data from the European satellite Sentinel-1: each color fringe represents a land subsidence of about 3 cm greater than the adjacent fringes. The ellipse indicates the area in which the greatest ground movements occurred, narrower in the north and wider in the south, extending approximately 40 km in length and approximately 15 km in width. Towards the inside of the ellipse, the lowering of the land increases until it reaches, near the town of Castelluccio di Norcia, about 70 cm vertically. Outside the ellipse, to the east and west, the ground has been lifted by a few centimetres. The green line represents the approximate course of the fault system that originated the various earthquakes in the sequence. On the line the tip of the triangles indicates the side where the blocks of the Earth's Crust are lowered along the fault surfaces. The green stars instead show the three major events of the sequence. The color fringes show a complex ground movement which highlights two distinct phenomena: seismic dislocation, i.e. the sliding of opposite blocks of the earth's crust along the deep fault surfaces that caused the three main earthquakes, and very superficial and localized movements such as fault scarps, reactivations of landslides and karst sinkholes. The general concentric pattern of the colored fringes is attributable to the rupture directly linked to the earthquake (the dislocation on the fault). While the interruptions, the thickenings or the acute angle bends of the fringes are due to more superficial breaking movements. This is the contribution that earthquakes, repeating themselves over time, provide to the construction of the Apennine landscapes. Using these and other data it is possible to reconstruct in detail the position and characteristics of the deep faults and therefore obtain very important information for the evaluation of the seismic sequence.
Figure 2:
The second figure shows in gray the 2 fault planes activated by the Amatrice earthquake of last August 24th and a possible reconstruction (not a model) of the fault plane on which the events of October 26th and 30th probably occurred, in pink .
GdL SAR, INGV - National Earthquake Centre