Controls on Bending‐Related Faulting Offshore of the Alaska Peninsula

Author:

Clarke Jacob12ORCID,Shillington Donna J.1ORCID,Regalla Christine1,Gaherty James B.1ORCID,Estep Justin1,Wiens Douglas A.3ORCID,Bécel Anne4ORCID,Nedimović Mladen R.5ORCID

Affiliation:

1. Northern Arizona University, School of Earth and Sustainability Flagstaff AZ USA

2. Southern Methodist University Dallas TX USA

3. Washington University in St Louis St Louis MO USA

4. Lamont‐Doherty Earth Observatory of Columbia University Palisades NY USA

5. Dalhousie University Halifax NS Canada

Abstract

AbstractOceanic plates experience extensive normal faulting as they bend and subduct, enabling fracturing of the incoming lithosphere. Debate remains about the relative importance of pre‐existing faults, plate curvature and other factors controlling the extent and style of bending‐related faulting. The subduction zone off the Alaska Peninsula is an ideal place to investigate controls on bending faulting as the orientation of the abyssal‐hill fabric with respect to the trench and plate curvature vary along the margin. Here, we characterize faulting between longitudes 161°W and 155°W using newly collected multibeam bathymetry data. We also use a compilation of seismic reflection data to constrain patterns of sediment thickness on the incoming plate. Although sediment thickness increases over 1 km from 156°W to 160°W, most sediments were deposited prior to the onset of bending faulting and thus should have limited impact on the expression of bend‐related fault strikes and throws in bathymetry data. Where magnetic anomalies trend subparallel to the trench (<30°) west of ∼156°W, bending faults parallel magnetic anomalies, implying that bending faults reactivate pre‐existing structures. Where magnetic anomalies are highly oblique (>30°) to the trench east of 156°W, no bending faults are observed. Summed fault throws increase to the west, including where pre‐existing structure orientations are constant (between 157 and 161°W), suggesting that another factor such as the increase in slab curvature must influence bending faulting. However, the westward increase in summed fault throws is more abrupt than expected for gradual changes in slab bending alone, suggesting potential feedbacks between pre‐existing structures, slab dip, and faulting.

Publisher

American Geophysical Union (AGU)

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