Assessing the feasibility of DInSAR for detecting coseismic deformation in small-magnitude earthquakes: the 2023 ML 4.4 Umbertide earthquake (Central Italy)

Differential Interferometric Synthetic Aperture Radar (DInSAR) techniques are largely used to detect coseismic deformation patterns associated with large-to-moderate magnitude earthquakes. In contrast, small earthquakes (M<5), although far more frequent and potentially crucial for understanding regional stress regimes and active faulting, generally produce weak surface deformation that is difficult to detect using remote sensing approaches.

In this work, we integrate relocated seismicity, observed DInSAR deformation, and the Okada elastic dislocation model to infer insights into the geometry and mechanics of the causative fault of the 2023 M_L 4.4 Umbertide extensional earthquake in Central Italy. The seismicity was relocated using the Non-Linear Earthquake Location Algorithm in combination with the three-dimensional velocity model developed specifically for the area.

We benefited of Sentinel-1 Line Of Sight (LOS) displacement maps generated over ascending and descending orbits through the EPOSAR service of the European Plate Observing System (EPOS) Research Infrastructure. These data were exploited to derive the vertical and east-west deformation components using a recently developed open-source Python tool capable of combining multiple LOS displacement maps. The results reveal up to ~2 cm of subsidence and ~1.5 cm of eastward motion in the epicentral area, suggesting the activation of a NE-dipping normal fault, consistent with the relocated seismicity distribution.

The focal mechanism parameters of this plane were adopted for the Okada modeling. According to the maximum-likelihood solution of the M_L 4.4 mainshock relocation, the source was modeled at 3.5 km of depth. The best-fitting solution between the modeled and observed deformation is a rectangular planar fault measuring 2.3 × 2.7 km (L × W), with a maximum slip of 20 cm.

Despite the earthquake’s limited magnitude and the surface deformation signal being partially affected by atmospheric disturbances, properly applied DInSAR techniques can provide a detailed estimation of surface displacement. The results demonstrate DInSAR’s ability to detect deformation induced by small-magnitude earthquakes in a seismically active region, with the potential to improve active fault mapping and seismic hazard assessment.