Abstract

We conducted discrete numerical simulations to examine the effects of seamount collisions with forearcs along actively accreting subduction margins. Modeled seamount interactions leave behind distinctive structures in overriding forearcs that differ from those found at non-accreting margins. Whereas accretion above a planar décollement produces evenly spaced thrust faults with uniform displacements, seamounts activate one or more large-offset splay faults that accommodate substantial offset. Locally oversteepened slopes develop above the seamounts, but in contrast to non-accreting margins, the steep slopes are transient. Renewed accretion following seamount passage allows the equilibrium surface slopes to recover. Seamounts also protect incoming strata in their wake, delaying formation of new thrust faults and increasing fault spacing. Weak horizons within accreting strata allow the décollement to step up above the seamount, further protecting deeper strata and vertically partitioning wedge deformation. Notably, all modeled faults form in sequence, in contrast to out-of-sequence faults found at non-accreting margins. Similar structures found at many accretionary margins, including Nankai (offshore Japan), suggest that we may underestimate the role of seamount interactions in many locations, with implications for our assessment of subduction hazards in these settings.

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