Caldwell J. G. Haxby W. F. Karig D. E. Turcotte D. L.. Sutton G. H. Maynard G. L. Hussong D. M.. Talwani M. Le Pichon X. Ewing M. Sutton G. H. Worzel J. L., Oxford University Press is a department of the University of Oxford. The cutting-edge capabilities of the Okeanos Explorer help to increase the scope and efficiency of ocean exploration. In both of these cases the driving mass has an optimum depth of about 100 km. Trenches in the Pacific are located in places where one tectonic plate subducts or slides under another one. A .gov website belongs to an official government organization in the Download image (jpg, 44 KB). A tsunami killed 40 people in NW Puerto Rico following a magnitude 7.3 earthquake in 1918. The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative Click image for larger view and image credit. [28], Currently, the static and time-variable Earth's gravity field parameters are being determined using modern satellite missions, such as GOCE, CHAMP, Swarm, GRACE and GRACE-FO. The free-air minimum east of the Lesser Antilles is related to underthrusting of the Caribbean plate by the Atlantic Ocean plate. The value of this excess mass depends upon more arbitrary assumptions for the crustal mass in the Puerto Rico Trench and its landward wall, but if the other assumptions above are realistic, the dense mass is required and is adequate to bend the surface down at the trench. In contrast, on its eastern boundary, the Caribbean overrides the North American plate, creating the island arc of the Lesser Antilles with its active volcanoes. towards 2541. [9], The terrain correction must be calculated for every point at which gravity is measured, taking into account every hill or valley whose difference in elevation from the measurement point is greater than about 5% of its distance from the measurement point. The free-air anomaly is also close to zero except near boundaries of crustal blocks. What is the thermal history of the arc massif, and its relation to, The Barbados Ridge complex lies east of the Lesser Antilles volcanic arc along the eastern margin of the Caribbean Plate. However, he found that the clock ran too slowly in Cayenne, compared with the apparent motion of the stars. A 6 month deployment of five ocean bottom seismographs recorded two such tightly clustered swarms, along with additional events. [10], The next correction is the free-air correction. Figure produced in Google Earth Pro. Other corrections are added for various gravitational models. Its northward edge is at a depth of 4,200 m, and its southern edge can be found on land in Puerto Rico at an elevation of a few hundred meters. The complex dates in part from the Eocene, and elements of the arc system. 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. Semantic Scholar is a free, AI-powered research tool for scientific literature, based at the Allen Institute for AI. Figure 4. Tectonophysics: Dynamics of lithosphere and mantle: general (1213); Tectonophysics: Dynamics: gravity and tectonics; Tectonophysics: Subduction zone processes (1031; Marine Geology and Geophysics: Subduction zone processes (1031; Geodesy and Gravity: Gravity anomalies and Earth structure (0920. At a minimum, these include the tidal correction gtid, the terrain correction gT, and the free air correction gFA. Earthquakes have been documented in the northeastern Caribbean since the arrival of Columbus to the Americas; written accounts of these felt earthquakes exist in various parts of the world. ago over a time period as short as 14 . Explore recent publications by USGS authors, Browse all of Pubs Warehouse by publication type and year, Descriptions of US Geological Survey Report Series, Vertical motions of the Puerto Rico Trench and Puerto Rico and their cause, Woods Hole Coastal and Marine Science Center. Figure 3. Over 4 million U.S. citizens live on these islands, mostly along the coast. E-mail Updates | User Survey | Contact Us | Report Error On This Page | Privacy Policy | Disclaimer | Site Info | Site Index The gravitational body force that acts on a flap of lithosphere, hanging in the aesthenosphere and more dense than it, pulls the lithosphere down at the trench. 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. The surveyed island, Anegada, is 120 km south of the Puerto Rico Trench and is near the, The Virgin Islands and Whiting basins in the Northeast Caribbean are deep, structurally controlled depocentres partially bound by shallow-water carbonate platforms. The seismogenic northeastern North America-Caribbean oblique-slip plate boundary includes the 8.5-km deep Puerto Rico trench, 120 km north of the densely populated islands of Puerto Rico and the, The results of drilling the Toa Baja hole will help answer some fundamental questions about the evolution of the Puerto Rico area. The proposed shear zone or tear is inferred from seismic, morphological, and gravity observations to start at the trench at 64.5W and trend southwestwardly toward eastern Puerto Rico. Because the island lies on an active plate boundary, earthquakes are a constant threat, and the densely populated coastal areas are vulnerable to tsunamis (Uri ten Brink, 2003). A 1918 magnitude 7.5 earthquake resulted in a tsunami that killed at least 40 people in northwestern Puerto Rico. Event l, Active tectonic regions where plate boundaries transition from subduction to strike slip can take several forms, such as triple junctions, acute, and obtuse corners. Some reports indicate that nearly 1,800 people drowned. 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. Privacy Policy Other Puerto Rican cities also have substantial risk.The hazard from tsunamis is also apparent. This glider will be recovered several months later by NOAA Ship Nancy Foster when she is operating in the area. The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. No. Exclusive Economic Zone surrounding Puerto Rico and the U.S. Virgin Islands, and the Puerto Rico Trench, as well as contribute to national ocean floor mapping priorities. The trench region may pose significant seismic and tsunami hazards to Puerto Rico and the U.S. Virgin Islands, where 4 million U.S. citizens reside. The active island arc of Lesser Antilles marks the junction between the Atlantic and Carribbean lithospheric plates. Essentially, all of the known causes of tsunamis are present in the Caribbean -- earthquakes, submarine landslides, submarine volcanic eruptions, subaerial pyroclastic flows into the ocean, and major tsunamis called teletsunamis. 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). Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative Similar convergence geometry is observed at the Challenger Deep in the Mariana Trench, the deepest point on Earth. Summary. If the Earth were an ideal oblate spheroid of uniform density, then the gravity measured at every point on its surface would be given precisely by a simple algebraic expression. Studies of free-air gravity anomaly profiles across island arcs show an important belt of positive anomalies seaward of deep-sea trenches. A draft U.S. Geological Survey (USGS) hazard map places equal probability for damaging ground motion for Mayaguez in western Puerto Rico as for Seattle, Washington. Historically, other large earthquakes have also struck the area, such as one in 1787 (magnitude~8.1), possibly in the Puerto Rico Trench, and one in 1867 (magnitude~7.5) in the Anegada Trough (figure 1). The M7.0 2010 Haiti earthquake epicenter was located on land 27 km north of the Caribbean Sea and its focal mechanism was oblique strike-slip. The density of crustal rock, , is usually taken to be 2670kg m3 so the Bouguer plate correction is usually taken as 0.3086 mgal m1 h. Here h is the elevation above the reference ellipsoid. Share sensitive information only on official, secure websites. [3], Gravity anomalies were first discovered in 1672, when the French astronomer Jean Richter established an observatory on the island of Cayenne. Download image (jpg, 50 KB). The tensile stresses necessary to deform or tear the slab could have been generated by increased curvature of the trench following a counterclockwise rotation of the upper plate and by the subduction of a large seamount. Because of its high population density and extensive development near the coast, Puerto Rico has a significant risk for earthquakes and tsunamis. 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. Leg 3 will include telepresence capability for all ROV dives, permitting the public to watch the expedition live and in action over the Internet. It is postulated that differential shifts between the Caribbean plate and the underthrust Atlantic plate have occurred at least twice, once in late Eocene to early Oligocene, during which the outer island chain of the northern Lesser Antillean arc was formed, and again sometime since the late Miocene, when the Barbados ridge and associated uplifted topography were formed. This platform was horizontally deposited over Cretaceous to Paleocene arc rocks starting in the Late Oligocene. [22], There are intense isostatic and free-air anomalies along island arcs. Rapid gravity computation for two dimensional bodies with application to the Mendocino submarine fracture zone, A crustal section across the Puerto Rico trench, Comments on paper by W. Jason Morgan, 'Gravity anomalies and convection currents, 2. The trench is less deep where the component of subduction is larger. Notice, Smithsonian Terms of 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. A .gov website belongs to an official government organization in the United States. Historically, other large earthquakes have also struck the area, such as one in 1787 (magnitude~8.1), possibly in the Puerto Rico Trench, and one in 1867 (magnitude~7.5) between St. Thomas ad St. Croixin the Anegada Trough. Thesis (Sc.D.) 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 USGS has an ongoing program to identify and map the faults in this region using various geophysical and geological methods in order to estimate the location and magnitude of potential earthquakes. http://oceanexplorer.noaa.gov/explorations/03trench/trench/trench.html. The unusually deep sea floor is not limited to the trench, but also extends farther south toward Puerto Rico. Click image for larger view and image credit. Noncommercial - you may not use this work for commercial purpose. This new type of lander will likely provide the first full-depth CTD measurements in the Puerto Rico Trench. This site uses cookies. This leg of the expedition will likely include exploration of deepwater canyons, seamounts, fish habitat, and possibly a mud volcano. The increased dip could have been caused by shearing or even by a complete tear of the descending North American slab, although the exact nature of this deformation is unknown. The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. Because the island lies on an active plate boundary, earthquakes are a constant threat, and the densely populated coastal areas are vulnerable to tsunamis. Here the axis of the free-air minimum lies very close to the eastern border of a zone of epicenters which apparently marks the commencement of crustal faulting along the underthrust. [26], Local anomalies are used in applied geophysics. Gravity anomalies and the origin of the Puerto Rico Trench P. Molnar Geology 1977 The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. However, the Earth has a rugged surface and non-uniform composition, which distorts its gravitational field. The proposed shear zone or tear is inferred from seismic, morphological, and gravity observations to start at the trench at 64.5? The Puerto Rico trench (PRT), with water depths of up to 8340 m, is the deepest part of the Atlantic Ocean, yet the relative plate motion along the PRT is predominantly strike slip with only a small component of North America (NOAM) plate subduction (N70E [ Calais et al., 2002; Mann et al., 2002 ]). During Leg 1 of this expedition, the ship will transit from her home port in North Kingstown, Rhode Island, to the U.S. ?W and trend southwestwardly toward eastern Puerto Rico. Dynamically triggered offshore aftershocks, caused by passing seismic waves from main shocks located on land, are currently not considered in tsunami warnings. Eyewitness reports of an 1867 Virgin Islands tsunami gave a maximum wave height of >7 m in Frederiksted, St. Croix, where a large naval vessel was left on top of a pier. Weather permitting scientists expect to execute 20 dives with NOAAs remotely operated vehicle (ROV) Deep Discoverer. There is a large Bouger positive, of over 350 mgal, beyond 1,000 kilometers (620mi) from the ridge axis, which drops to 200 over the axis. This belt of positive anomalies is called the Outer Gravity High. Site Info, NOAA Ocean Exploration Its depth is comparable to the deep trenches in the Pacific Ocean. The line of trend of historic volcanoes of the Lesser Antillean arc is equidistant (160 km) from the axis of minimum free-air anomaly. the Puerto Rico Trench is also characterized by the most negative free-air gravity anomaly on Earth,-380 mGal, located 50 km south of the trench, where water depth is 7950 m (Fig ure 2). Conf., Geol. The trench itself is very negative,[23] with values more negative than 250 mgal. II - The Puerto Rico trench and the mid- Atlantic rise. [15], The Bouger anomaly map of the Alps shows additional features besides the expected deep mountain roots. Agreement NNX16AC86A, Journal of Geophysical Research (Solid Earth), Is ADS down? In addition to continued mapping of the region, Leg 2 will include deployments of a new type of benthic lander, a data collector moored to the ocean floor for an extended period of time. Notice, Smithsonian Terms of The opposite is true for the theoretical case of terrain that is completely uncompensated: The Bouger anomaly is zero while the free-air and Airy isostatic anomalies are very positive. This brings the free-air anomaly, which omits the correction terms for either, close to zero. The residual gravity anomalies are then consistent with the existence of a subcrustal dense mass, that could be the hanging slab of lithosphere. The tensile stresses necessary to deform or tear the slab could have been generated by increased curvature of the trench following a counterclockwise rotation of the upper plate and by the subduction of a large seamount. [2] Gravity on the surface of this reference ellipsoid is then given by a simple formula which only contains the latitude. A tilted carbonate platform provides evidence for extreme vertical tectonism in the region.This platform was horizontally deposited Images of the slope north of Puerto Rico disclose massive slope failure scars, as much as 50 km across, that probably generated tsunamis along the north shore of the island. below sea level under the ocean basin, 12 km under the Caribbean Sea, at about 16 km under the trench, and at slightly shallower depth under Puerto Rico. The free-air anomaly is around +70 mgal along the Andes coast, and this is attributed to the subducting dense slab. The Puerto Rico Trench and the Mid-Atlantic Rise, Gravity anomalies seaward of deep-sea trenches and their implications, Geophysics-steered self-supervised learning for deconvolution, Local estimation of quasi-geostrophic flows in Earths core, Bayesian Detectability of Induced Polarisation in Airborne Electromagnetic Data, Analytical computation of total topographic torque at the Core-Mantle Boundary and its impact on tidally driven Length-of-Day variations, The ground deformation of the south-eastern flank of Mount Etna monitored by GNSS and SAR interferometry from 2016 to 2019, Volume 233, Issue 3, June 2023 (In Progress), Volume 233, Issue 2, May 2023 (In Progress), Volume 233, Issue 1, April 2023 (In Progress), Volume 234, Issue 1, July 2023 (In Progress), Geomagnetism, Rock Magnetism and Palaeomagnetism, Marine Geosciences and Applied Geophysics, https://doi.org/10.1111/j.1365-246X.1977.tb04215.x, Receive exclusive offers and updates from Oxford Academic, Copyright 2023 The Royal Astronomical Society. 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