Derek Neuharth, Whitney M Behr, Adam F Holt
SUMMARY The strength of the subduction interface plays a major role in controlling subduction dynamics on both local and global scales. While previous studies have primarily examined interface strength in 2-D models, natural subduction zones are inherently 3-D, with interface strength varying along-strike due to spatial differences in factors such as sediment input. Here, we use the geodynamic code ASPECT to conduct fully dynamic 3-D subduction models in which interface strength varies along-strike. We find that the interaction between strong and weak segments of the interface leads to a narrower range of convergence velocities while broadening the range of viable interface stresses compared to 2-D or homogeneous 3-D models. Stronger segments, when adjacent to weaker ones, exhibit increased convergence velocities. This promotes higher interface stresses and facilitates the subduction of otherwise stagnant strong segments. We find that the interface viscosity of the strong segment controls the baseline stress, whereas the viscosity contrast along-strike controls the magnitude of amplification of the stress due to velocity increases. The elevated interface stresses at strong segments also generate greater compressional forces in the overriding plate than expected from 2-D models. Combined with along-strike variations in convergence velocity, this results in trench migration, with stronger segments displaying more advanced trench positions relative to weaker segments. Possible natural analogues include the Bolivian Orocline in the central Andes and the Lesser Antilles, both of which show enhanced overriding plate compression and trench advance in areas of reduced sediment supply.