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244-1 Subduction Zone Obliquity and Trench-Parallel Inner Forearc Deformation

Session: Subduction Zone Processes: Insights from Geology, Geochemistry, and Petrochronology

Presenting Author:

Kristin Morell

Authors:

Morell, Kristin¹, Finley, Theron², Harrichhausen, Nicolas³, Gilroy, Kellan⁴

(1) The University of California, Goleta, CA, USA, (2) University of Victoria, Victoria, BC, Canada, (3) University of Alaska, Anchorage, Anchorage, AK, USA, (4) University of California, Santa Barbara, Santa Barbara, 93106, USA,

Abstract:

Subduction zones are defined by plate convergence, yet their upper plates exhibit a wide range of deformation styles globally. While various hypotheses have been proposed to explain this global variability, the controlling factors remain poorly understood. We analyzed ~24,000 km of active global subduction zones to investigate how subduction obliquity influences trench-parallel and horizontal deformation in the overriding plate. Using global datasets of GNSS velocities and active fault catalogs, we examined inner deformation across 13 forearcs on both short (decadal) timescales, captured by GNSS, and long (millennial to million-year) timescales, inferred from trench-parallel active strike-slip faults. Our results reveal a strong link between subduction zone obliquity and both the sense and magnitude of upper plate rotation observed in GNSS data, as well as the sense and rate of deformation along trench-parallel strike-slip faults. Unlike earlier studies suggesting that obliquity only influences deformation above a certain threshold, we find that even low to moderate obliquity affects forearc behavior. High-obliquity margins, such as New Zealand and the Philippines, show the highest GNSS-derived vorticity and cumulative slip rates on trench-parallel strike-slip faults. In contrast, lower-obliquity regions, like portions of Cascadia and Peru, exhibit reduced vorticity and either diffuse strike-slip faulting or broadly distributed deformation. Across all forearcs, we find strong correlations between obliquity and both GNSS vorticity and trench-parallel fault slip rates. The results challenge the notion that significant forearc deformation requires high obliquity and underscore the fundamental role of subduction obliquity in dictating upper plate deformation globally.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5850

Subduction Zone Obliquity and Trench-Parallel Inner Forearc Deformation

Description

Session Format: Oral

Presentation Date: 10/22/2025

Presentation Start Time: 08:10 AM

Presentation Room: HBGCC, 217C

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