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The relationship between seismic deformation and deep seated gravitational
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Abstract
This paper re-evaluates the origin of some peculiar patterns of ground deformation observed by
space geodetic techniques during the two earthquakes of September 26th of the Colfiorito seismic
sequence. The surface displacement field due to the fault dislocation, as modeled with the classic
Okada elastic formulations, shows some areas with high residuals which cannot be attributed to
unsimulated model complexities. The latter was investigated using geomorphological analysis, by
recognising the geologic evidence of deep seated gravitational slope deformations (DSGSD) of the
block-slide type. The shape and direction of the co-seismic ground displacement observed in these
areas are correlated with the expected pattern of movement produced by the reactivation of the
identified DSGSD. At least a few centimetres of negative Line of Sight ground displacement was
determined for the Costa Picchio, Mt. Pennino, and Mt. Prefoglio areas. A considerable horizontal
component of movement in the Costa Picchio DSGSD is evident from a qualitative analysis of
ascending and descending interferograms. The timing of the geodetic data indicates that the ground
movement occurred during the seismic shaking, and that it did not progress appreciably during the
following months. In this work it has been verified the seismic triggering of DSGSD previously
hypothesized by many authors. A further implication is that in the assessment of DSGSD hazard it is
necessary to consider the seismic input as an important cause of acceleration of the deformation rates