Geological review of the Alaska-Aleutian Arc and exploration of 3D subduction zone modeling

Abstract

The Alaska-Aleutian subduction system spans more than 3,000 km along the northern boundary of the Pacific Ocean and is the location of both devastating earthquakes and frequent volcanic eruptions. The potential for loss of life and destruction compels us to study the nature of the Alaska-Aleutian subduction system. However, numerous studies have raised more questions than they have answered, illuminating the complex nature of this arc such as changes in arc water content along arc, trench parallel shear wave splitting directions, and locked versus slipping regions of the subducting and overriding plate. A necessary component to understanding the complexities of this arc is 3D subduction zone models. I have verified that the 3D thermal and velocity models using the Sepran finite element package correspond to previously published 2D. However, 3D model resolution no greater than 2 km in the mantle wedge region where temperature and velocity change most rapidly is necessary. The desired mesh resolution requires that the mesh spanning the Alaska Peninsula to the western Aleutians must comprise more than 23 million elements. The Sepran package version 0310 is limited to 4 Gb of memory per core or roughly 2 million elements and does not support parallel programming. Thus in order to run the full 23 million element Alaska-Aleutian model, the newest version of Sepran 0315 which does support parallel programming must be utilized. Finally, solving for velocity in the subducting slab of a large, variable slab shape often results in violations of conservation of mass as required for the Boussinesq approximation. A combination of defining velocity parallel to the incoming plate velocity to a depth of 170 km in the slab followed by a method that defines velocity according to the elements dip is the best approach to minimizing deformation in the subducting slab.