The outermost surface expression of a subduction zone is the accretionary wedge, a mountain fold belt built up above sea level by the underthrust ocean crust.

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The outermost surface expression of a subduction zone is typically a deep ocean trench, not an accretionary wedge. An accretionary wedge forms from sediments scraped off the subducting plate and accumulates above the trench, but it is not the outermost feature.

The Outermost Surface Expression of a Subduction Zone Is the Accretionary