Click image for larger view and image credit. This gravity anomaly can reveal the presence of subsurface structures of unusual density. Abstract The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide, This PDF is available to Subscribers Only. Peter Molnar, Gravity anomalies and the origin of the Puerto Rico Trench, Geophysical Journal International, Volume 51, Issue 3, December 1977, Pages 701708, https://doi.org/10.1111/j.1365-246X.1977.tb04215.x. ) or https:// means youve safely connected to the .gov website. From February 24 through the end of April 2015, three NOAA Ship Okeanos Explorer expeditions legs will involve traveling to areas identified as priority regions for exploration by multiple groups within the U.S. Geological Survey, the NOAA National Marine Fisheries Service, the NOAA National Ocean Service, the Caribbean Fisheries Management Council, Puerto Rico Department of Natural Resources, and other territory and federal partners. The gravity anomaly is the difference between the observed acceleration of an object in free fall (gravity) near a planet's surface, and the corresponding value predicted by a model of the planet's gravitational field. Many tectonic models have been proposed to explain this geologically fascinating, tectonically active region; however, none have gained acceptance, and the region remains poorly understood, largely because its underwater location makes it difficult to study. 5, Puerto Rico Trench negative gravity anomaly belt, The Caribbean: gravity field and plate tectonics, Geophysical investigation of the Puerto Rico Trench and outer ridge, Seismic refraction and reflection measurementsPuerto Rico outer ridge, Continuous seismic profiles of the outer ridge and Nares basin north of Puerto Rico, Geophysical study of Antilles outer ridge, Puerto Rico trench, and northeast margin of Caribbean Sea, On the applicability of a universal elastic trench profile, Seismic refraction and reflection in Caribbean Sea, Crustal and upper mantle structure of the Central Aleutian Arc, Evidence for high density crust and mantle beneath the Chile trench due to the descending lithosphere, The Kuril Trench-Hokkaido Rise system: Large shallow earthquakes and simple model of deformation, The present day motions of the Caribbean plate, Paleogeography and geologic history of Greater Antilles, The relationship between bathymetry and gravity in the Atlantic Ocean, Tectonics of the Caribbean and Middle America regions from focal mechanisms and seismicity, Gravity anomalies and convection currents 1. The theoretical value of gravity can be corrected for altitude and the effects of nearby terrain, but it usually still differs slightly from the measured value. The rocks are naturally full of fractures and faults and given enough push, some of these faults may move abruptly to relieve the stress;causing earthquakes. Search for other works by this author on: Attribution: You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work). In both of these cases the driving mass has an optimum depth of about 100 km. Studies of free-air gravity anomaly profiles across island arcs show an important belt of positive anomalies seaward of deep-sea trenches. Determining wh, Waters from the Atlantic Ocean washed southward across parts of Anegada, east-northeast of Puerto Rico, during a singular event a few centuries ago. Semantic Scholar is a free, AI-powered research tool for scientific literature, based at the Allen Institute for AI. Motion along its northern boundary (in the plate boundary zone region) is dominantly strike-slip (sideways motion between the plates), with a small component of subduction (one plate sinks under the other plate). The low-density sediments of the Molasse basin produce a negative anomaly. The gravitational body force that acts on a flap of The Puerto Rico Trench is the deepest part of the Atlantic Ocean, with water depths exceeding 8,300 meters. Results of the seismic investigation of the Puerto Rico trench and outer ridge, carried out in 1959 by Lamont Geological Observatory, Woods Hole Oceanographic Institution, A. and M. College of Texas, New seismic and magnetic information from the Antilles Outer Ridge and Trench region has been combined with previous geophysical observations to provide an explanation for the origin of the crust, A crustal section across the Puerto Rico Trench, from 450 km north to 250 km south of San Juan, was deduced from seismic refraction and gravity data. A study of the seismic velocity structure of the subcrustal oceanic lithosphere was conducted in the western North Atlantic north of the Lesser Antilles, where the age of the lithosphere, We infer from the bathymetry and gravity field and from the source mechanisms and depths of the eight largest earthquakes in the Bali region that the Bali Basin is a downwarp in the crust of the, Abstract Velocity modeling and earthquake relocation are used to examine the structure and seismicity of an area south of the Puerto Rico trench in the northeast Caribbean, and to explore whether and, We have determined focal mechanisms for the largest earthquake (Ms = 7.8) recorded instrumentally in the Caribbean Basin, the August 4, 1946, Hispaniola earthquake, and three of its large-magnitude, The direction and rate of movement of the Caribbean plate with respect to North America are determined from the slip vectors of shallow earthquakes and from the configuration of downgoing seismic, We have developed two-dimensional spherical shell finite element models of elastic displacements in the North America-Caribbean (NA-Ca) plate boundary zone (PBZ) in order to quantify crust and fault. Different theoretical models will include different corrections to the value of gravity, and so a gravity anomaly is always specified with reference to a particular model. The terrain correction is calculated from knowledge of the local topography and estimates of the density of the rock making up the high ground. Site Info, NOAA Ocean Exploration By determining the likely hazards and their causative mechanisms and providing this information to government agencies and the public, the USGS can aid in such activities as improvement of building codes, encouraging safer zoning, and assisting public education for response to hazards. Just offshore of Puerto Rico and the U.S. Virgin Islands are a diversity of deep-sea features that include the deepest trench in the North Atlantic Ocean; seamounts; and numerous submarine canyons, valleys, and troughs. The higher terrain is held up by the buoyancy of thicker crust "floating" on the mantle. This site uses cookies. For example, the formation and sinking of a lithospheric root may explain negative isostatic anomalies in eastern Tien Shan. A crustal section across the Puerto Rico trench, J. geophys. Click image for larger view and image credit. (2011), Significant earthquakes on the Enriquillo fault system, Hispaniola, 1500-2010: Implications for seismic hazard, Geomorphic and stratigraphic evidence for an unusual tsunami or storm a few centuries ago at Anegada, British Virgin Islands, Inland fields of dispersed cobbles and boulders as evidence for a tsunami on Anegada, British Virgin Islands, Pacific Coastal and Marine Science Center. Cooling of continental lithosphere by thermal conduction to the surface following a heating event imposes a load on the lithosphere and causes subsidence as the basement rocks contract. Gravity anomalies are modelled assuming that the crustal thicknesses of the Atlantic and Caribbean Oceans are constant (but different) and that the Atlantic Ocean floor seaward of the outer rise, Puerto Rico, and the Caribbean Sea floor are each in isostatic equlibrium. Other margins of the island (west, south, and south west) are also associated with massive tectonic features and may pose addtional hazard. We document the spatial and temporal variability of. The Puerto Rico trench negative free-air gravity anomaly belt extends from south of Barbados, around the Antillean arc, to eastern Cuba. Studies of free-air gravity anomaly profiles across island arcs show an important belt of positive anomalies seaward of deep-sea trenches. With the exception of the alkali basalts of Grenada, the volcanics of the arc can, The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. Both these effects reduce the value of gravity, explaining why Richter's pendulum clock, which depended on the value of gravity, ran too slowly. The unusually deep sea floor is not limited to the trench, but also extends farther south toward Puerto Rico. Res., 64, 1545. An official website of the United States government. Secure .gov websites use HTTPS Download image (jpg, 44 KB). Bathymetry collected by Okeanos Explorer and University of New Hampshire Law of the Sea Project is shown in the background and gray boxes show the extent of existing Okeanos Explorer mapping surveys in the Atlantic. (or is it just me), Smithsonian Privacy Then, at 3.5 Ma, the carbonate platform was tilted by 4 toward the trench over a time period of less than 40 kyr, such that its northern edge is at a depth of 4000 m and its reconstructed elevation on land in Puerto Rico is at +1300 m (Figures 1 and 2). ROV dives will mostly be conducted during the day, while CTD casts, and multibeam, singlebeam, and sub-bottom acoustic mapping will occur at night when the ROV is on deck. This expedition will include some of the deepest dives in this region and the deepest dive ever for the Deep Discoverer at 6,000 meters. We explore the interaction between thrust events on the subduction interface and strike-slip faults within the forearc region using 3-D models of static Coulomb stress change. Other corrections are added for various gravitational models. National Oceanic and Atmospheric Administration. The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. The Puerto Rico Trench, in contrast, is located at a boundary between two plates that slide past each other with only a small component of subduction. A tilted carbonate platform provides evidence for extreme vertical tectonism in the region. 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