Strike-slip 23 January 2018 MW 7.9 Gulf of Alaska rare intraplate earthquake: Complex rupture of a fracture zone system

• Published in: Scientific Reports
• Main Authors: Krabbenhoeft, Anne, von Huene, Roland, Miller, John J., Lange, Dietrich, Vera, Felipe
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Research 2018
• Subjects: Gulf of Alaska; Kodiak; Alaska
• Online Access: https://oceanrep.geomar.de/id/eprint/44294/; https://oceanrep.geomar.de/id/eprint/44294/1/Krabbenhoeft.pdf; https://oceanrep.geomar.de/id/eprint/44294/7/41598_2018_32071_MOESM1_ESM.pdf; https://doi.org/10.1038/s41598-018-32071-4

Large intraplate earthquakes in oceanic lithosphere are rare and usually related to regions of diffuse deformation within the oceanic plate. The 23 January 2018 MW 7.9 strike-slip Gulf of Alaska earthquake ruptured an oceanic fracture zone system offshore Kodiak Island. Bathymetric compilations show a muted topographic expression of the fracture zone due to the thick sediment that covers oceanic basement but the fracture zone system can be identified by offset N-S magnetic anomalies and E-W linear zones in the vertical gravity gradient. Back-projection from global seismic stations reveals that the initial rupture at first propagated from the epicenter to the north, likely rupturing along a weak zone parallel to the ocean crustal fabric. The rupture then changed direction to eastward directed with most energy emitted on Aka fracture zone resulting in an unusual multi-fault earthquake. Similarly, the aftershocks show complex behavior and are related to two different tectonic structures: (1) events along N-S trending oceanic fabric, which ruptured mainly strike-slip and additionally, in normal and oblique slip mechanisms and (2) strike-slip events along E-W oriented fracture zones. To explain the complex faulting behavior we adopt the classical stress and strain partitioning concept and propose a generalized model for large intra-oceanic strike-slip earthquakes of trench-oblique oriented fracture zones/ocean plate fabric near subduction zones. Taking the Kodiak asperity position of 1964 maximum afterslip and outer-rise Coulomb stress distribution into account, we propose that the unusual 2018 Gulf of Alaska moment release was stress transferred to the incoming oceanic plate from co- and post-processes of the nearby great 1964 MW 9.2 megathrust earthquake.