Earthquake Relocations Delineate a Discrete Fault Network and Deformation Corridor Throughout Southeast Alaska and Southwest Yukon

• Published in: Tectonics (Washington, D.C.) D.C.), 2024-05, Vol.43 (5), p.n/a
• Main Authors: Biegel, K. M., Gosselin, J. M., Dettmer, J., Colpron, M., Enkelmann, E., Caine, J. S.
• Format: Article
• Language: English
• Subjects: active tectonics; Catalogues; Connectors; Continental crust; Deformation; earthquake focal mechanisms; earthquake relocations; Earthquakes; Eastern Denali fault; Fault lines; Faults; Glaciers; Mapping; Mountain glaciers; Plate boundaries; Plate tectonics; Plates; Satellite imagery; Seismic activity; Seismicity; seismogenic thickness; Seismometers; Subduction; Tectonics; Yakutat collision
• ISSN: 0278-7407; 1944-9194
• DOI: 10.1029/2023TC008140

Deformation in southeastern Alaska and southwest Yukon is governed by the subduction and translation of the Pacific‐Yakutat plates relative to the North American plate in the St. Elias region. Despite notable historical seismicity and major regional faults, studies of the region between the Fairweather and Denali faults are complicated by glacial coverage and the remote setting. In the last decade, significant improvements have been made to the density of regional broadband seismometer networks. We relocate more than 5,000 earthquakes between 2010 and 2021 in the region of southeastern Alaska and southwestern Yukon utilizing these improved seismic networks. With reductions in catalog uncertainty, particularly in depth, we quantify the thickness of the seismogenic layer in the crust throughout the region and locate seismicity on a shallow network of upper‐crustal faults. Relocated earthquakes, combined with an updated focal‐mechanism catalog, permit estimating and classifying motion of active faults. This includes mapping the Totschunda‐Fairweather “Connector” fault, which plays an important role in explaining regional deformation, and identifying new faults like the Kathleen Lake fault. We draw similarities between our seismic observations and simplified conceptual models of regional tectonics, which describe a dominant transpressional regime and localized slip partitioning. Our results support a hypothesis where current deformation is taking place on a well‐defined and evolved network of shallow faults in the corridor between the Totschunda‐Fairweather “Connector” and Denali faults. Plain Language Summary Southeastern Alaska and southwest Yukon are actively deforming due to their position at the collision of multiple tectonic plates as the Pacific plate and the Yakutat microplate collide with the North American plate. The region has a large number of significant earthquakes and many mapped faults. Traditional methods of identifying faults, such as field mapping or remote satellite imagery, are complicated due to the remote setting, large glaciers, and mountainous terrain. Here, we analyzed more than 5,000 earthquakes from 2010 to 2021 to better understand how deformation occurs and where active faults are located. Our results show that earthquakes occur on a shallow network of faults, confirming models of an actively deforming and uplifting continental crust. We can map and classify motion on new faults, such as the “Connector” fault, showing that deforma