Collaborative Research: Seismic Hazard, Lithosphere Hydration, and Double-Verging Structure of the Puerto Rico Subduction Zone: A Seismic Reflection and Refraction Perspective

The Puerto Rico Trench (PRT) poses major earthquake and tsunami hazards. Tsunamis generated at this subduction zone may also impact the U.S. East Coast. This project supports land and sea seismic experiments across the PRT and Puerto Rico. The experiments will define the detailed seismic structure of the PRT, advance our understanding of the PRT, and improve hazard assessment. The project consists of: (1) Three wide-angle seismic reflection/refraction profiles using ocean bottom seismometers (OBS); (2) Seven multichannel seismic (MCS) reflection profiles, two parallel to and inland from the trench, and five across the trench. (3) An array of 100 short-period land nodal seismometers deployed across the Puerto Rico island. The project will provide support for training several graduate students and an early career scientist, as well as research opportunities for faculty and students at a minority serving institution. This project supports an active-source seismic experiment across the Puerto Rico Trench (PRT), its outer rise, and across the Puerto Rico island arc. The PRT is a highly oblique subduction zone, where old Atlantic plate subducts under the Caribbean plate at a slow rate. The PRT is associated with anomalous and unexplained characteristics, such as the widest trench (below 6,000 m), the lowest gravity anomaly on Earth, and anomalous subsidence of the north coast of Puerto Rico. This project will acquire, analyze, and interpret multiple types of data: Three wide-angle seismic reflection/refraction profiles across the PRT with OBSs, with one of the lines extending to south of the Puerto Rico island and including an array of land nodal seismometers deployed across the Puerto Rico island; seven MCS reflection profiles, two parallel and five perpendicular to the PRT axis; and multibeam bathymetry, 3.5 kHz sub-bottom profiler, gravity, and magnetics. The experiments are designed to address three key questions: (1) What is the shallow geometry of the subducting slab and its lateral continuity along the 500-km section of the trench? (2) What are the degree and spatial extent of hydration of the Atlantic lithosphere entering the Puerto Rico Trench? (3) Does oceanic bivergent thrust system represent double-sided subduction or a crustal retro-wedge of one-sided subduction? The integrated seismic experiments, together with the other ancillary geophysical datasets, will produce two-dimensional seismic reflection images, P-wave and S-wave travel-time tomography 2-D models, and gravity-derived density models of the study region. These results are expected to significantly advance our understanding of the above scientific questions and assessment of the PRT seismic and tsunami hazard. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.