Abstract

The source geometry of the 24 August 2016 Amatrice earthquake is studied with Sentinel 1‐A/B and Advanced Land Observation Satellite (ALOS)‐2 Interferometric Synthetic Aperture Radar (InSAR) coseismic observations. Without presetting the fault geometry and location, we allow these geodetic data to constrain a planar fault and a listric dislocation through an innovative nonlinear approach. Finite‐element models (FEMs) are built to simulate the earthquake deformation over a domain with a distribution of realistic crustal materials. Optimal fault geometries are resolved with the observed coseismic displacements in both homogeneous (HOM) half‐spaces and heterogeneous (HET) FEMs. The HET‐computed planar slip is modeled next to the hypocenter and estimated with a very compatible dip (47°) similar to the moment tensor solution, while that of the HOM solution is offset by 14°. Meanwhile, the former recovers the coseismic displacements significantly better than the latter at 95% confidence. This indicates that the inverse solutions of source analysis are sensitive to the presence of nonuniform rock materials in the elastic domain. Though abundant fault detachments are documented within the epicentral area, the slip distributions derived along optimized listric faults do not improve the prediction of surface movements estimated by the rectangular sources. This implies that a planar fault geometry is sufficient to describe the rupture of the Amatrice earthquake. The corresponding slip distribution reveals a maximum slip of 1  m at 7 km depth, beneath a lithological boundary between the shallow weaker units and the underlying stronger Dolomite. A significant correlation is found between the slip magnitude and subsurface rock stiffness where stress is being accumulated, implying a possible structural control on the earthquake nucleation and propagation.

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