The b $b$ -Value Tomography of the Calabrian Arc

Abstract

In the Calabrian Arc subduction zone, the notable lack of seismicity at depths near 100 km strongly suggests the presence of slab detachment. Contrary to typical patterns, where $b$-values decrease with depth, our b-value mapping reveals unexpectedly high $b$-values at these depths. Within the 100–150 km depth interval, the gradient of the $b$-value reaches its peak, indicating a significant reduction in stress. We propose four potential interpretations for these observations: (a) fluid-induced weakening due to dehydration processes, (b) heterogeneity at the slab tip reducing rupture propagation, (c) creeping zone behavior at the detachment tip, and (d) post-detachment damage to the rocks, leaving them unable to support stress. These hypotheses remain beyond experimental verification at present. This study underscores the complex interplay of geological processes at depth and their implications for seismic hazard assessment in subduction zones.