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Is the Source of the 1918 Puerto Rico Tsunami a Landslide or a Fault Rupture? a View From the Sea Floor

Description: 

The October 11, 1918, devastating tsunami in northwest Puerto Rico, had been used as an example for earthquake-induced landslide tsunami hazard. Three pieces of evidence pointed to a landslide as the origin of the tsunami: the discovery of a large submarine landslide scar from bathymetry data collected by shipboard high-resolution multibeam sonar, reported breaks of submarine cable within the scar, and the fit of tsunami models to flooding observations. Newly processed seafloor imagery collected by remotely-operated-vehicle (ROV) show, however, pervasive Fe-Mn crust (patina) on the landslide walls and floor, indicating that the landslide scar is at least several hundred years old. ¹⁴C dates of sediment covering the landslide floor verify this interpretation. Although we have not searched the region systematically for an alternative tsunami source, we propose a possible source, a two-segment normal fault rupture along the eastern wall of Mona Rift. The proposed fault location matches published normal faults with steep bathymetry and is close to the ISC-GEM catalog locations of the 1918 main shock and aftershocks. ROV observations further show fresh vertical slickensides and rock exposure along the proposed fault trace. Hydrodynamic models from a Mw7.2 earthquake rupture along the eastern wall of the rift faithfully reproduce the reported tsunami amplitudes, polarities, and arrival times. Our analysis emphasizes the value of close-up observations and physical samples to augment remote sensing data in natural hazard studies.

Session: Active Faults in the Caribbean and Central America [Poster]

Type: Poster

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Uri S. ten Brink

Student Presenter: No

Invited Presentation: No

Authors