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Upper Plate Stress in the Alaskan Continental Crust: Spooky Interactions at a Variety of Distances

Description: 

To understand the impacts of Alaska-Aleutian subduction on the overlying crust and far-field continental interior, we compile moment tensors from 3048 earthquakes in the Alaskan continental crust. Inverting these provides the first comprehensive statewide stress map, first Alaskan stress model update in 15 years, and the first to take advantage of improved coverage from the Earthscope Transportable Array.

Subduction controls near-field stress. Reverse-oblique faulting accommodates radial crustal shortening around the flat-slab segment in southcentral Alaska, from Cook Inlet to the northern Alaska Range foothills and all along the Denali/Totschunda fault system. Similarly, radial shortening around the Yakutat block occurs by reverse faulting. Above the slab tear between these two, however, NW–SE lower crustal extension may result from increasing buoyancy due to heating and underplating beneath Prince William Sound, the western Chugach and Talkeetna Mountains. The Queen Charlotte-Fairweather system transitions from oblique shortening near Yakutat Bay to strike-slip and then to oblique extension south of Haida Gwaii; tsunamigenic potential cannot be fully understood without accounting for this along-strike transition in faulting style.

Plate-boundary compression wanes with distance into the continent, controlling maximum stress directions but giving way to variable intraplate deformation. Strike-slip with secondary N–S contraction dominates the upper Yukon basin and eastern Brooks Range. Between the Tintina and Kaltag faults, maximum stress is consistently NNW–SSE, yet secondary extension replaces contraction. This trend continues westward: Despite compressive boundary tractions, oblique extension is widespread across western Alaska. In the Purcell and Baird Mountains, Seward Peninsula and diffusely across southwest Alaska, primarily strike-slip motion includes significant NNE–SSW stretching roughly parallel to the distant plate boundary, suggesting escape tectonics. Equal parts normal and strike-slip faulting accommodate NW–SE extension in the western Aleutian backarc and ESE–WSW extension in the Bering Sea.

Session: Structure and Behavior of the Alaska-Aleutian Subduction Zone - II

Type: Oral

Date: 5/3/2024

Presentation Time: 10:30 AM (local time)

Presenting Author: Will

Student Presenter: No

Invited Presentation: 

Authors