Sediment-dominated forearcs of the northern Barbados Ridge, southern Mexico, and landward of the Nankai Trough show evidence of accretion of deep-sea and trench sediments in the style of fold-and-thrust belts; sediments are imbricately offscraped at the base of the trench slope and underplated at greater depths, perhaps locally via duplex accretion. Diminishing seismic coherence of accreted deposits during uplift suggests continuing structural evolution and dewatering, with the final result resembling the stratally disrupted accretionary complexes exposed on land. Fold-and-thrust style deformation is therefore a transient structural state in many accretionary wedges.
Sediment starved forearcs off Guatemala and the Marianas are underlain by igneous basement of either oceanic or volcanic-arc origin. Most of the oceanic sediment of the subducting plate is thrust beneath the base of the trench slope with little if any accretion. Underthrust sediment may be underplated or subducted. The seaward margin of the Mariana forearc has been tectonically truncated; Guatemala may have been either tectonically truncated or the site of prolonged subduction without accretion.
Forearc evolution off northern Japan involves superposition of differing tectonic regimes with tectonic erosion followed by accretion.