Rapid detection of complex deformation pattern following strong earthquakes through DInSAR measurements: the October 2016 central Italy case

In the last three decades, remote sensing techniques, such as Differential Synthetic Aperture Radar Interferometry (DInSAR), Lidar differencing, optical imagery, and Global Positioning System (GPS) have been exploited for investigating, with high accuracy, ground displacement phenomena. Large seismic events (M_w > 5.5) can trigger deformations at the surface, such as ruptures related to the activation of main active faults and/or other deformations induced by seismic shaking (e.g., landslides, creeping, sinkhole).

In 2016-2017, a long earthquake sequence struck the Apennines in central Italy, producing impressive surface ruptures attributed to the 24 August Mw 6.0 and 30 October Mw 6.5 main-shocks. These ruptures were investigated and mapped by field geologists soon after the earthquakes.

We present detailed maps of the surface deformation pattern produced by the M. Vettore Fault System during the October 2016 earthquakes. The DInSAR analysis have been retrieved from ALOS-2 SAR data, via the Parallel Small BAseline Subsets (P-SBAS) algorithm. On these maps, we trace a set of cross-sections to analyse the coseismic vertical displacement, essential to identify both surface fault ruptures and off-fault deformations.

At a local scale, we identify a lower number of coseismic ruptures respect to the ones recognised in the field, but they are in very good agreement and even more laterally continuous. At a larger scale, we observe the M. Vettore Fault System hanging-wall being characterized by a long-wavelength upward-convex curvature, which is less evident towards the south and locally interrupted by a steep vertical gradient, testifying the occurrence of an antithetic NE-dipping fault.

A quantitative comparison of DInSAR- and field-derived vertical displacement reveals that our approach is particularly effective to constrain ruptures characterized by spatial vertical displacement up to 50 – 60 cm, which, in the field, show an unclear lateral continuity.

The rapid detection of deformation patterns from DInSAR technique can furnish important constraints on the activated fault segments, their spatial distribution and interaction soon after the seismic events. Thanks to the large availability of satellite SAR acquisitions, the proposed workflow can be potentially applied worldwide. It might be fundamental not only to support field geological mapping activities during an ongoing seismic crisis but also to provide a wider and faster picture of surface ruptures crucial for emergency management by civil protection in densely populated areas.