A Chicken and Egg Dilemma: Forearc Strain Field and Seismic Behavior in the Andreanof Segment.
What determines megathrust slip behavior in subduction zones is still under debate, and the relationship between the preferred slip style over short, earthquake-cycle time scales and long-term patterns of deformation also remains poorly understood. We collected multichannel seismic data, USGS legacy reflection data, and gravity data in the Andreanof segment of the Aleutian Islands to address these questions. This region presents contrasting seismic and locking behavior from west to east. There is a higher recurrence of large earthquakes and tsunamis and higher coupling in the western section. Moreover, the oblique subduction leads to strain partitioning. As a consequence, the upper plate developed strike-slip faults and rotating blocks, impacting the distribution of compressional and extensional stress.
Observations indicate distinct forearc deformation styles in the eastern region (Atka) and the western region (Adak). Atka has a wide forearc basin with flat layers, whereas Adak shows more compression by uplifting the frontal prism and forearc basin shortening, which correlates with the higher recurrence of megathrust earthquakes. Adak shows intracrustal reflectors that could be magmatic intrusions, underplating, or old deformational features.
The incoming plate properties, sediments, and trench infill show similar characteristics in the entire Andreanof segment. Thus we propose that over-riding plate properties contribute to the different seismic and deformational styles. The combination of differences in rheology due to magmatic intrusions, underplating, and/or pre-existing deformation and differences in tectonic stress associated with rotating blocks and the strike-slip systems could impact fault development and changes in forearc permeability. We explore the hypothesis that the higher shortening in the western section could be more efficient in releasing pore fluid pressure, increasing the effective stress, which promotes coupling and deformation.
Session: Structure and Behavior of the Alaska-Aleutian Subduction Zone - II
Type: Oral
Room: Tikahtnu Ballroom A
Date: 5/3/2024
Presentation Time: 10:45 AM (local time)
Presenting Author: Valeria Cortés Rivas
Student Presenter: Yes
Additional Authors
Valeria Cortés Rivas Presenting Author Corresponding Author vc553@nau.edu Northern Arizona University |
Donna Shillington Donna.Shillington@nau.edu Northern Arizona University |
Dan Lizarralde dlizarralde@whoi.edu Woods Hole Oceanographic Institution |
Hannah Mark hmark@whoi.edu Woods Hole Oceanographic Institution |
Brian Boston boston@auburn.edu Auburn University |
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A Chicken and Egg Dilemma: Forearc Strain Field and Seismic Behavior in the Andreanof Segment.
Category
Structure and Behavior of the Alaska-Aleutian Subduction Zone
Description