High-resolution seismic tomography across the 1980 (Ms 6.9) Southern Italy earthquake fault scarp

A high-resolution multi-fold wide-angle seismic
survey carried out across the Irpinia fault, Southern Italy,
yields new information about the shallow structure of this
normal fault that was reactivated in 1980. The fault zone is
imaged to a depth of about 60 m by using a non-linear
tomographic technique that is specially designed to image
strongly heterogeneous media. Results confirm the location
of the fault, as previously inferred by a trench excavated in
soft soils, and clearly delineates a 30–35 m step in the
bedrock. This single step is indicative of a narrow fault
zone, which corresponds upward to warped soils exposed in
the trench, thus demonstrating that the near-surface warping
is directly related to a brittle faulting in the bedrock.
Assuming that the vertical slip rate yielded by paleoseismic
data (0.25–0.35 mm/yr) has been constant since the fault’s
inception, the latter should date back to about 100–140 kys
ago. Such a young age may explain why the Irpinia fault is
not associated with evident, large-scale geomorphic
indicators of its activity.

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