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Insights Into Inherited Crustal Features and Southern Alaska Tectonic History From Sp Receiver Functions and Seismicity

Description: 

The deformation history of the crustal blocks across southern Alaska and geometric history of the bounding faults reflect both inherited features and subsequent convergent margin events. Multiple dense (<20-km spacing) arrays of broadband seismometers across southern Alaska have previously allowed for imaging of crustal structure across the region using various seismic imaging methods. Here, we employ S-to-P receiver functions to investigate the crustal structure of southern Alaska for signals of dynamic tectonic activity. The subduction zone plate interface and subducting slab Moho are imaged dipping at shallow (<60-km) depths across the southernmost part of the subduction zone, in agreement with previous P-to-S receiver function imaging. Along two different transects, an inland-dipping (~15°) boundary is imaged intersecting the trace of the Border Ranges Fault at the surface. This feature may represent an unrotated paleo-subduction (Mesozoic) interface. This observation is combined with previous seismic imaging along both the Border Ranges Fault and the next seaward terrane-bounding fault—the Contact Fault—to examine along-strike gradients in the dip of these structures and the relationship between their variable rotation and the history of convergent tectonics along the margin. Along with large (>10-km) crustal thickness offsets imaged across both the Denali Fault system and the Eureka Creek Fault, these features provide a test of previous hypotheses for subduction polarity in the region. Additionally, a sharp positive velocity gradient with increasing depth is imaged at ~25-km beneath the Copper River Basin, which is most easily explained as a shallow Moho and may be related to the generation of a new Wrangell Volcanic Field volcano, resulting from the underlying tear in the subducting slab. New tremor and low-frequency earthquake locations across the Copper River Basin region contrast with these seismic imaging results and raise questions about the structure and dynamics surrounding the tear in the subducting Yakutat slab.

Session: Structure and Behavior of the Alaska-Aleutian Subduction Zone [Poster Session]

Type: Poster

Date: 5/3/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Michael

Student Presenter: No

Invited Presentation: 

Authors