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Newly Discovered Tsunami Deposit in Northwest Puerto Rico Supports a Pre-Columbian Megathrust Earthquake on the Puerto Rico Trench That Generated an Atlantic-Wide Tsunami

Description: 

The written record of Caribbean tsunamis extends back over 500 years, but does not include one generated by a great earthquake (> Mw 8.0) on the megathrust at the Puerto Rico Trench. We cored a coastal mangrove pond at East Bajura near Isabela in Northwest (NW) Puerto Rico to search for tsunami deposits from a possible megathrust earthquake. The pond extends inland 150 to 350 meters from a sandy beach, spans about 1 km in the alongshore direction, and is 0.5 meters above present sea level. Pleistocene eolianites 5-10 m high, with gaps, protect the pond from swells. Pond sediments are predominately mud or mangrove peat. More than 30 sediment cores document a thin (1- 7 cm thick) sand sheet at about 60 cm depth throughout the pond. This layer exhibits suspension grading, an erosive basal contact, and an organic cap which suggest deposition from a high energy flow, most likely a tsunami. An event-free Bayesian age-depth model using radiocarbon dates of plant macrofossils above and below the sand sheet constrain the timing of deposition to 1470 to 1530 CE. This age overlaps in age with tsunami deposits emplaced between 1200 and 1500 CE on the coasts of the islands of Saint Thomas, Anegada, Saba, and Anguilla, approximately 200-400 km to the east of East Bajura, that face the Puerto Rico Trench. Modeling by Codrie et al. (2022) of an approximately 200-km long rupture on the Puerto Rico Trench from Saint Thomas to Anguilla indicates a tsunamigenic Mw 8.7 megathrust earthquake is required to account for the pre-Columbian tsunami deposits observed in the Lesser Antilles. Pre-Columbian tsunami deposits from NW Puerto Rico suggests a plausible rupture length of 400 km, which would result in a greater magnitude earthquake and a tsunami that would effect both Caribbean and Atlantic coasts. Future work using the inland extent and elevation of correlated tsunami deposits and tsunami modeling will better constrain the pre-Columbian earthquake and tsunami in the Caribbean.

Session: Active Faults in the Caribbean and Central America

Type: Oral

Date: 4/20/2023

Presentation Time: 10:45 AM (local time)

Presenting Author: Bruce Jaffe

Student Presenter: No

Invited Presentation: 

Authors