Evidence for Holocene Earthquakes along the Húsavík-Flatey Fault in North Iceland: Implications for the Seismic Behavior of Oceanic Transform Faults

• Published in: Bulletin of the Seismological Society of America
• Main Authors: Matrau, Rémi, Klinger, Yann, Thorðarson, Thorvaldur, Guðmundsdóttir, Esther R., Avşar, Ulas, Parisi, Laura, Fittipaldi, Margherita, Jonsson, Sigurjon
• Other Authors: Physical Sciences and Engineering, Physical Science and Engineering (PSE) Division, Earth Science and Engineering, Earth Science and Engineering Program, Université de Paris Cité, Institut de Physique du Globe de Paris, CNRS, Paris, France, Faculty of Earth Sciences, University of Iceland, Reykjavík, Iceland, Middle East Technical University (METU), Ankara, Türkiye
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Seismological Society of America (SSA) 2024
• Subjects: Húsavík; Iceland; Flatey
• Online Access: http://hdl.handle.net/10754/697852; https://doi.org/10.1785/0120230119

Understanding the long-term seismic behavior of oceanic transform faults is challenging because their location underwater generally prevents the use of classical paleoseismological techniques. The Húsavík-Flatey fault (HFF) in northern Iceland, however, is a partially emerged oceanic transform fault accommodating 6–9 mm/yr of deformation, offering a unique opportunity to apply classic inland paleoseismic methods to decipher the Holocene earthquake history of an oceanic transform fault. We excavated three fault-orthogonal paleoseismic trenches at two locations on the HFF and identified nine surface rupturing earthquakes in the last 6–8 ka. We observe little to no deformation associated with the most recent large earthquakes of 1872 (Mw ∼6.5) and the penultimate earthquake in 1755 (Mw ∼7), suggesting that these earthquakes may have occurred mainly offshore, ruptured a fault strand not sampled here, or that their magnitudes may have been overestimated. From our observations, we estimate a return time of 600 ± 200 yr for the largest earthquakes on the HFF (Mw 7.2–7.3), and we suggest that the known historical earthquakes are likely not representative of the largest possible earthquakes on the fault. Furthermore, our observations suggest a quasi-periodic behavior and support the quasi-repeating earthquake sequences observed from instrumental earthquake catalogs on several oceanic transform faults. The authors thank associate editor of BSSA, Thomas Brocher, and the two reviewers Katherine Scharer and Glenn Biasi for their thorough review of the article and the many helpful comments and suggestions for improving the article. This research was supported by King Abdullah University of Science and Technology (KAUST) under Award Number BAS/1/1353-01-01. This research was also supported by the Agence Nationale de la Recherche (ANR—French National Agency for Research) under the project ANR-18-C31-0012. The authors thank Gaukur Hjartarson at the Norðurthing municipality in Húsavík for granting access to the two trench sites ...