The Formation of Forearc Seismic Belt: A Potential Explanation of Seismogenesis in a Weakly Coupled Subduction Zone

The enigmatic occurrence of seismic activity in forearc regions, particularly within weakly coupled subduction zones, continues to perplex geoscientists. While traditional models of plate interface coupling explain many megathrust earthquakes, they fall short in accounting for the spatial distribution and mechanism of intermediate-magnitude earthquakes within the forearc crust. This opinion article explores the formation of the forearc seismic belt (FSB) as a plausible and coherent framework for understanding seismogenesis in such settings. Drawing from geophysical observations, recent advances in subduction zone modeling, and tectonic analogs, the article argues that the FSB emerges as a structural and stress-response feature linked to lower plate geometry, fluid fluxing, and crustal heterogeneities in the overriding plate. This perspective challenges the narrow view that only strongly coupled megathrust interfaces are responsible for major seismicity and proposes that crustal adaptation to slab dynamics plays a more active role. Recognizing the FSB’s role could refine seismic hazard assessments in subduction zones previously thought to be relatively quiescent.