Puerto Rico–Virgin Islands fault zone

Puerto Rico–Virgin Islands fault zone
Name	Puerto Rico–Virgin Islands fault zone
Location	Caribbean Sea
Country	Puerto Rico, United States Virgin Islands
Plate	North American Plate, Caribbean Plate
Type	Right-lateral strike-slip
Status	Active

Puerto Rico–Virgin Islands fault zone The Puerto Rico–Virgin Islands fault zone is an active fault system located north of Puerto Rico and west of the Leeward Islands, forming a major plate-boundary structure between the North American Plate and the Caribbean Plate. The zone links plate boundary features near the Puerto Rico Trench, the Muertos Trough, and the Anegada Passage, and it influences seismicity across Hispaniola, the British Virgin Islands, and the United States Virgin Islands. This fault zone has been studied in the context of significant events such as the 1918 1918 San Fermín earthquake and tsunami, the 1943 1943 Aceh earthquake (for methodological parallels), and modern investigations by institutions including the United States Geological Survey, Scripps Institution of Oceanography, and the Lamont–Doherty Earth Observatory.

Geography and extent

The fault zone trends east–west and extends from the vicinity of the Puerto Rico Trench westward through the waters north of Puerto Rico to the area of the Anegada Passage, bordering the islands of Culebra, Vieques, and the U.S. Virgin Islands such as Saint Thomas and Saint John. It connects to bathymetric and structural elements including the Mona Canyon, the Mona Rift, and the Muertos Trough, and interacts with the northern margins of Hispaniola near the Cordillera Central. Offshore mapping campaigns by organizations like the National Oceanic and Atmospheric Administration and the Northeastern University investigation teams have used multibeam bathymetry to delineate scarps, submarine channels, and deformational features across the continental slope and the Puerto Rican Shelf.

Tectonic setting and structure

Situated at the boundary between the North American Plate and the Caribbean Plate, the fault zone accommodates relative plate motion through a complex interplay of transform faulting, strike-slip segments, and local thrusts linked to subduction at the Puerto Rico Trench. Structural interpretations identify right-lateral strike-slip faults, en echelon fault arrays, pull-apart basins, and transpressional uplifts akin to structures seen along the San Andreas Fault and the Enriquillo–Plantain Garden fault zone. Geologic features implicated include segmented fault strands that link with the Anegada Passage transfer zone and the offshore continuation toward the Muertos Trough, with measured slip rates constrained by paleoseismology, GPS networks operated by University of Puerto Rico, and marine geophysical profiles from research vessels such as the NOAAS Ronald H. Brown.

Seismicity and historical earthquakes

Seismicity along the zone includes moderate to large earthquakes recorded in instrumental catalogs maintained by the United States Geological Survey, the International Seismological Centre, and regional observatories like the Puerto Rico Seismic Network. Historically notable events affecting the region include the 1918 earthquake and tsunami that struck Aguadilla, Puerto Rico and the Sombrero Island region, the 1787 and 1867 earthquake reports compiled by contemporary chroniclers, and swarm activity reported near the Mona Passage. Probabilistic seismic hazard analyses for San Juan, Puerto Rico and Charlotte Amalie incorporate scenarios from the fault zone and adjacent structures such as the Muertos Trough and the Puerto Rico Trench to estimate ground shaking, liquefaction, and building-code implications studied by FEMA and academic teams at Rensselaer Polytechnic Institute.

Tsunami potential and hazard assessment

Because segments of the fault zone lie beneath shallow shelf areas and link to the deep Puerto Rico Trench, rupture scenarios can generate tsunamis that threaten the Leeward Islands, the northern shores of Puerto Rico, and the U.S. Virgin Islands. Tsunami modeling by the National Tsunami Hazard Mitigation Program and numerical studies using codes developed at Scripps Institution of Oceanography and NOAA examine both coseismic sea-floor displacement and secondary sources such as submarine landslides in the Mona Canyon. Historical tsunami observations from 1918 and inferred paleotsunami deposits studied by teams at the Smithsonian Institution and Florida International University inform evacuation planning, early warning strategies, and inundation maps used by municipal authorities in Mayagüez, Puerto Rico and island emergency managers.

Geologic studies and mapping

Geologic and geophysical investigations combine marine multibeam bathymetry, seismic reflection profiling, sub-bottom coring, and land-based paleoseismology to characterize fault geometry, slip rates, and recurrence intervals; notable projects include collaborative cruises involving NOAA Ship Okeanos Explorer, the R/V Marcus G. Langseth, and university-led efforts from University of Puerto Rico at Mayagüez. Published work in journals such as Bulletin of the Seismological Society of America and Geology documents stratigraphic evidence for past earthquakes, tsunami deposits near Añasco, and tectonic uplift along coastal terraces correlated with radiocarbon dating performed at the Woods Hole Oceanographic Institution. Mapping efforts feed into regional geological maps produced by the United States Geological Survey Caribbean geologic mapping program.

Monitoring and risk mitigation

Monitoring networks include seismic stations of the Puerto Rico Seismic Network, broadband instruments maintained by the Incorporated Research Institutions for Seismology, and continuous GNSS arrays operated by the University of Puerto Rico and international partners like UNAVCO. Risk mitigation measures emphasize building-code updates influenced by studies from the Federal Emergency Management Agency, community preparedness initiatives coordinated with Red Cross chapters, tsunami early warning integration with NOAA Pacific Tsunami Warning Center protocols, and land-use planning informed by hazard maps used by municipal planners in San Juan and Ponce, Puerto Rico. Continued investment in offshore mapping, paleoseismic trenching, and public education by institutions such as the Caribbean Disaster Emergency Management Agency aims to reduce exposure to seismic and tsunami threats across affected islands.

Category:Seismic zones Category:Geology of Puerto Rico Category:Geology of the Caribbean