← Back to Sessions

20th-Century Interseismic Deformation in the Lesser Antilles Subduction Zone From Coral Microatolls

Description: 

The earthquake and tsunami potential of the Lesser Antilles megathrust is poorly known, despite the hazard it poses to numerous island populations and its proximity to the Americas. While the fault has not produced large earthquakes in the instrumental era, historical records of great earthquakes in the 19th century and earlier, which were likely megathrust ruptures, suggest that the subduction is not entirely aseismic. We used coral microatoll paleogeodesy to study century-scale vertical deformation in the northern Lesser Antilles. Only one microatoll has been found that is old enough to potentially record 19th-century earthquakes, and no “fossil” microatolls have been found that might record earlier events. However, we found many sites with microatolls recording 20th-century vertical deformation, which demonstrate that the eastern coasts of the forearc islands have been subsiding by up to ∼8 mm/y relative to sites closer to the arc. Modeling this deformation as the result of underlying strain accumulation on the megathrust suggests that a portion of the megathrust interface just east of the forearc islands has been locked during the 20th century. If this model is correct, the accumulated strain detected by microatoll studies will likely be released in future megathrust earthquakes, uplifting previously subsiding areas and potentially causing widespread damage from strong ground motion and tsunami waves.

Reconciling our results with decadal-scale instrumental geodesy has proven challenging. Models of instrumental horizontal deformation suggest little or no strain accumulation anywhere along the Lesser Antilles megathrust, and instrumental vertical deformation shows subsidence averaging 1–2 mm/y across the Lesser Antilles, variable between neighboring sites and with varying degrees of agreement with our data. The discrepancy with our results can potentially be explained by the different time scales of measurement, as recent studies elsewhere have indicated that interseismic coupling patterns may vary on decadal time scales and that century-scale or longer records are required to fully assess seismic potential.

Session: Active Faults in the Caribbean and Central America

Type: Oral

Date: 4/20/2023

Presentation Time: 02:15 PM (local time)

Presenting Author: Belle Philibosian

Student Presenter: No

Invited Presentation: 

Authors