Constraints on the Structure of the Border Ranges Fault System, Kenai Peninsula, Alaska from the Preliminary Results of the 3D Inversion Model of Gravity Data

Abstract

We tested plausible initial 3D density models across the eastern Cook Inlet basin to constrain the geometry of the Border Ranges fault system (BRFS). The BRFS forms the structural boundary between the forearc-arc structures and accretionary terranes of the Aleutian subduction zone in southern Alaska. We used 2D density cross-sections as starting â??a prioriâ?? models to constrain the 3D inversion model. We computed the theoretical gravity based on the inversion, compared it to the observed gravity, and determined the gravity misfit. We tested the 3D inversion solutions on the lowland regions where the densest spacing of gravity points is located using three surfaces defining the topographic ground level, the top and base of the sediment layers within Cook Inlet basin to build the preliminary 3D models. Preliminary results show the 3D inversion is able to constrain the simple shape of Cook Inlet basin with geologically reasonable densities. We will produce several alternative starting models for the entire Cook Inlet forearc basin and the BRFS. The most reasonable models will be used as starting models for the structure of the entire study area.