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

Abstract

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.