Controls on bending-related faulting offshore of the Alaska Peninsula

• Main Author: Clarke, Jacob W
• Format: Thesis
• Language: English
• Published: 2022
• Subjects: QE Geology; Alaska Amphibious Community Seismic Experiment (AACSE); Alaska
• Online Access: https://openknowledge.nau.edu/id/eprint/5859/; https://openknowledge.nau.edu/id/eprint/5859/1/Clarke_2022_controls_on_bending-related_faulting_offshore_alaska_penin.pdf

Bathymetric, seismic reflection, and modelling studies have demonstrated that subducting oceanic plates experience extensive normal faulting as they bend and subduct at the trench axis. However, the relative importance of pre-existing (usually abyssal-hill) faults, plate curvature and other factors in controlling the extent and style of bending-related faulting remain debated. The subduction zone off the Alaska Peninsula is an ideal place to investigate controls on outer-rise faulting. Pre-existing abyssal-hill fabric in the study area, inferred to be parallel to magnetic anomalies, show a range of orientations, from east-west trends west of a remnant triple junction at 158W and north-south oriented trends to the east. The orientation of the trench itself varies smoothly over this region, and plate curvature gradually increases to the west. Previous studies with limited data suggest that the style and magnitude of bending faulting also varies along this subduction zone. We analyze new multibeam bathymetry data collected as a part of the Alaska Amphibious Community Seismic Experiment (AACSE) to characterize bending faulting between longitudes of 161W and 156ºW. We also used a compilation of legacy and recently acquired seismic reflection data to constrain patterns of sediment thickness on the incoming plate, since sediment has the potential to mask bending faulting. Finally, we estimated along-strike changes in the degree of slab bending by calculating the bending from the seafloor and the top of oceanic crust, which was estimated using the sediment thickness map. Comparisons between trends of outer-rise faults and magnetic anomalies imply that orientations of faults are strongly influenced by pre-existing structures. We observe a decrease in summed scarp heights from west to east, with the highest amount of faulting in the Shumagin Gap region. Sediment cover increases from west to east, which has the potential to mask bending faulting outboard of the Semidi segment where we observe little to no seafloor fault ...