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Linking Subduction-earthquake Supercycles with Coastal Uplift in South Chile

Description: 

Ranges in recurrence of megathrust earthquakes allows them to be grouped into earthquake cycles within supercycles. We use coastal stratigraphy and soils on raised intertidal deposits at Isla Guafo, 60 km landward of the south Chile trench, to infer land-level changes associated with great subduction earthquakes, and numerical models to infer the relations of the changes with plate-boundary slip. Guafo was uplifted ~4 m during the 1960 earthquake (M9.5) and has been subsiding rapidly since at ~16 mm/yr from continuous GPS. Subsidence was interrupted by 11 cm of uplift during the 2016 earthquake (M7.6). Five soils, each developed on coseismically uplifted intertidal deposits, were buried during the past 1.7 ka. The sequence of soils and deposits suggests land-level changes similar to those observed during and after 1960. Such repeated changes can be modeled as elastic strain accumulation and release in the shallow segment of the plate-boundary. However, distinct changes in coastal morphology and stratigraphy suggest Guafo was permanently uplifted during an earthquake in AD ~800. This age range overlaps the time when sequences of subsided buried soils at Chucalén and Maullín, located at 120 and 140 km from the trench, respectively, show an abrupt change in lithology suggesting uplift. If the change records permanent uplift at Maullín during the same earthquake, slip in the deeper segment of the plate boundary is required. However, we cannot yet determine if the uplift occurred during of shortly after the earthquake. Uplift at these three sites is associated with emerged coastal terraces, suggesting a link with permanent coastal uplift. Such events that slip (either co- or aseismically) down to the continental mantle apparently have millennial recurrence times instead of centuries as for 1960-type events rupturing the shallower segment.

Session: From Earthquakes to Plate Boundaries: Insights Into Fault Behavior Spanning Seconds to Millennia [Poster]

Type: Poster

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Daniel Melnick

Student Presenter: No

Invited Presentation: 

Authors