The GPS Geodetic Infrastructure in the Puerto Rico and Virgin Islands Region and Its Applications for Faulting, Landslide, and Sea-Level Change Study

The Puerto Rico and Virgin Islands (PRVI) are located within the complex plate boundary zone between the North American and Caribbean plates in the northeastern Caribbean Sea. The interaction of geophysical risk and human settlement makes the region especially vulnerable to natural hazards, such as earthquakes, tsunamis, landslides, hurricanes, and flooding. This region is one of the earliest places that employed high-accuracy Global Positioning System (GPS) technology to study plate tectonics and natural hazards. A dense Continuously Operating Reference Stations (CORS) network with 24 permanent GPS stations is currently jointly operated by academic, government, and local land surveying communities. We summarize the current GPS geodetic infrastructure in the PRVI region: a dense CORS network, a stable local reference frame, and sophisticated GPS data processing software packages. We established a stable Puerto Rico and Virgin Islands reference frame (PRVI14), which is essential to precisely delineate local ground deformation in the space and time domains. The current geodetic infrastructure in the PRVI region can distinguish ground deformation as slow as 0.4 mm/year and 0.5 mm/year in the horizontal and vertical directions, respectively. Our study shows the island of St. Croix is moving away from the PRVI region toward southeast at a steady velocity of 1.7 mm/year; the Lajas Valley in southwestern Puerto Rico is experiencing a north-south extension (1.5 mm/year) and a minor right-lateral strike slip (0.4 mm/year) with respect to PRVI14. We developed a workflow for conducting millimeter-accuracy landslide monitoring without installing any reference stations in the field, which is more efficient than the conventional differential positioning method. We performed a GPS, tide gauge, and satellite altimeter integrated sea-level change study in the PRVI and the whole Caribbean region. Our results show that current absolute sea-level rise rate along PRVI coasts is 1.7±0.3 mm/year, according to the tide gauge dataset from 1955 to 2015. The sea-level change rates have considerable temporal and spatial variabilities, and estimates may be subject to the techniques used and observation periods in the Caribbean Sea. It is expected that our study will promote applications of GPS techniques in natural hazards research and mitigation in the PRVI region and in other areas prone to natural hazards.Earth and Atmospheric Sciences, Department o