TSUNAMI POTENTIAL OFFSHORE NW PUERTO RICO II: REVALUATING THE SOURCE OF THE 1918 PUERTO RICO TSUNAMI

Proposed seafloor deformation mechanisms for generating tsunamis oftentimes produce equivocal, if not controversial, results. Although tsunamis immediately following large earthquakes are routinely associated with the predicted earthquake-induced seafloor deformation, submarine slides, which accompany large earthquakes, may also trigger significant tsunamis. Thus, one of the great challenges in tsunami research today is to accurately determine the origin of the seafloor deformation that best reproduces observed tsunami waves. Previous wave models for the tsunami that inundated northwest Puerto Rico immediately following the great (M 7.3) 1918 earthquake assume the tsunami was caused by seafloor fault motion that accompanied the earthquake. Although these models accurately predict tsunami arrival times and amplitudes at many local sites, some discrepancies exist between observed and predicted wave phase, amplitude, and timing. These discrepancies likely stem from (1) relatively weak constraints on the exact size, location, and offset of regional faults, (2) low bathymetric resolution, and (3) the existence of previously unaccounted-for submarine landslides that may have caused or distorted the tsunami. A recently compiled data set from multiple cruises over the past 12 years enable us to reduce these discrepancies and both identify and constrain the location and size of submarine slides and active faults near the epicenter of the 1918 earthquake (See adjoining poster). We use these data to reassess the shape, size, and magnitude of seafloor deformation caused by the 1918 earthquake and possible submarine slides. Finally, we incorporate these interpretations into several 3D tsunami wave models to estimate what seafloor deformation scheme best replicates the observed tsunami. The analysis highlights how high-resolution multibeam data coupled with side-scan sonar and seismic images can improve our understanding of earthquake-induced seafloor deformation and the resulting tsunami it generates. Ultimately, coring and dating of related sediments will allow us to identify which deposits/faults are associated with the 1918 event.