Mechanical Essence of Double-Arc Formation Along the Eastern Aleutian Subduction Zone

Abstract

The free-air gravity anomaly along the Aleutian subduction zone exhibits a single set of negative and positive trench-parallel belts in the western region, whereas it exhibits doubled negative–positive trench-parallel belts in the eastern region. The eastern inner–western positive gravitational belt corresponds to the topographic chain of the Alaska Peninsula and the Aleutian Islands. However, the eastern outer positive gravitational belt does not coincide with the chain of the topographic outer-arc highs. In this study, we determined the across-trench profiles of the plate interface geometry for the western and eastern Aleutian subduction zones on the basis of the hypocentre distribution. The surface uplift rates computed from the dislocation-based two-dimensional subduction model for the Aleutian plate interface profiles adequately reproduced the western single-arc and eastern double-arc characteristics. The essential factors of the double-arc formation are a low subduction dip angle and a bimodal plate interface curvature distribution within the elastic lithosphere. The double-arc highs of the computed uplift rates more closely coincided with the gravitational highs than the current topographic highs. This implies that tectonic events in the past caused the topographic activity shift towards the continental shelf edge and the subsequent topographic readjustment under the current tectonic state.