Graph from the paper.
Age of splay faulting events at Montague Island (colored curves) and of regional megathrust Alaskan earthquakes (black curves). The overlap of four out of eight events suggests synchronization of splay faulting and megathrust ruptures over multiple seismic cycles. Credit: DePaolis et al. [2024], Figure 8
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Solid Earth

Splay faults are secondary structures in the upper plates of subduction zones that have commonly accompanied great historical megathrust earthquakes, adding additional sources to tsunami generation, landslides, and coastal land-level changes. However, their recurrence times and synchronization with the megathrust over multiple seismic cycles remain poorly understood because finding geologic archives with sufficient resolution for paleoseismic reconstructions has been challenging.

Using stratigraphy and detailed analyses of diatoms – fossils that record relative sea-level positions – DePaolis et al. [2024] reconstructed land-level changes over the past 4,200 years at Montague Island, Alaska. Surface ruptures from slip along the Patton Bay splay fault were documented at Montague Island during the great 1964 Prince Williams Sound earthquake, providing a key modern analogue to interpret the geologic record.

The authors interpreted land-level changes during earthquakes from abrupt contacts between intertidal silt and coastal peat layers. They quantified these changes using variations in diatom assemblages across such contacts and estimated their ages using radiocarbon analyses finding evidence for at least 3 meters of uplift during the 1964 and three previous earthquakes. The ages of these earthquakes overlap with the regional chronology of great Alaskan megathrust earthquakes, suggesting that splay faulting at Montague Island occurred during 4 of a total of 8 great earthquakes. These results are important as they emphasize the need to consider splay faults as secondary hazard sources in subduction zones.

Citation: DePaolis, J. M., Dura, T., Witter, R. C., Haeussler, P. J., Bender, A., Curran, J. H., & Corbett, D. R. (2024). Repeated coseismic uplift of coastal lagoons above the Patton Bay splay fault system, Montague Island, Alaska, USA. Journal of Geophysical Research: Solid Earth, 129, e2023JB028552. https://doi.org/10.1029/2023JB028552

—Daniel Melnick, Associate Editor, JGR: Solid Earth

Text © 2024. The authors. CC BY-NC-ND 3.0
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