For example, the formation and sinking of a lithospheric root may explain negative isostatic anomalies in eastern Tien Shan. The trench is less deep where the component of subduction is larger. Because of its high population density and extensive development near the coast, Puerto Rico has a significant risk for earthquakes and tsunamis. Below are other science projects associated with this project. Because the island lies on an active plate boundary, earthquakes are a constant threat, and the densely populated coastal areas are vulnerable to tsunamis. Salt domes are typically expressed in gravity maps as lows, because salt has a low density compared to the rocks the dome intrudes. 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. Website Satisfaction Survey
Parts of the Puerto Rico Trench were previously Understanding continental slope morphological evolution is essential for predicting depositional systems and reservoirs in the adjacent basin. 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. Some reports indicate that nearly 1,800 people drowned. Exclusive Economic Zone surrounding Puerto Rico and the U.S. Virgin Islands, and the Puerto Rico Trench. Google Scholar. Joint analyses of the ocean bottom seismographs and land-based seismic data reveal that the swarms are locat, Historical records indicate frequent seismic activity along the north-east Caribbean plate boundary over the past 500 years, particularly on the island of Hispaniola. Because the island lies on an active plate boundary, earthquakes are a constant threat, and the densely populated coastal areas are vulnerable to tsunamis. ago over a time period as short as 14-40 kyr. Erosion is a concern in many coastal areas, but is particularly serious to island economies that rely heavily on the tourist industry. This latter deformation caused the disappearance of a trench opposite the southern Lesser Antillean arc and a displacement of the Puerto Rico trench axis oceanward away from the axis of the negative free-air anomaly belt near the northeast corner of the Caribbean plate. Holocene and Pleistocene tectonic deformation of the coast in the Mexico subudction margin is recorded by geomorphic and stratigraphic markers. This comparison, though of limited application to other places, helps calibrate coastal geology for assessment of earthquake and tsunami potential along the Antilles Subduction Zone. Correcting for these effects removed most of this anomaly. Conf., Geol. For a measurement point above the reference ellipsoid, this means that the gravitational attraction of the bulk mass of the earth is slightly reduced. 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 ]). Noncommercial - you may not use this work for commercial purpose. Crossref. I explain these vertical movements by a sudden increase in the slab's descent angle that caused the trench to subside and the island to rise. ago over a time period as short as 14-40 kyr. 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. Careful analysis of the gravity data allows geologists to make inferences about the subsurface geology. Puerto Rico, the Virgin Islands to its east, and eastern Hispaniola to its west, are located on an active plate boundary zone between the North American plate and the northeast corner of the Caribbean plate. ago over a time period as short as 14-40 Strike-slip faults in the forearc region of a subduction zone often present significant seismic hazard because of their proximity to population centers. LockA locked padlock The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. Seattle). 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. Agreement NNX16AC86A, Journal of Geophysical Research (Solid Earth), Is ADS down? These satellite missions aim at the recovery of a detailed gravity field model of the Earth, typically presented in the form of a spherical-harmonic expansion of the Earth's gravitational potential, but alternative presentations, such as maps of geoid undulations or gravity anomalies, are also produced. Because of its high population density and extensive development near the coast, Puerto Rico has a significant risk for earthquakes and tsunamis. This is tedious and time-consuming but necessary for obtaining a meaningful gravity anomaly. 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. 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. Download image (jpg, 44 KB). Astrophysical Observatory. 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). Subsequent cooling thickens the lithosphere again and subsidence takes place. We study the oblique convergence of the NOAM and CARIB plates between southeastern Cuba to northern Puerto Rico, A post-hurricane survey of a Caribbean island affords comparisons with geologic evidence for greater overwash at the same place. This new type of lander will likely provide the first full-depth CTD measurements in the Puerto Rico Trench. Image courtesy of the NOAA Office of Ocean Exploration and Research. subducts, or slides, under another one. Earthquakes and tsunamis in Puerto Rico, the Virgin Islandsand adjacent islands are mostly caused by the convergence of the North American tectonic plate with the Caribbean tectonic plate on which the islands are located. The crustal thickness and the free-air anomaly computed for sinkers of different sizes and depths are then compared with the measured freeair anomalies and seismic depths of the Puerto Rico trench and the mid-Atlantic rise. The . 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. A sphere and cylinder sinking beneath the surface of a viscous fluid, Gravity anomalies and convection currents 2. The Puerto Rico Trench is also associated with the most negative gravity anomaly on earth, -380 milliGal, which indicates the presence of an active downward force. Lateral variations in gravity anomalies are related to anomalous density distributions within the Earth. Many tectonic models have been proposed to explain this geologically fascinating, tectonically active region; however, none has gained acceptance, and the region remains poorly understood, largely because its underwater location makes it difficult to study. The Puerto Rico Trench is the deepest part of the Atlantic Ocean, with water depths exceeding 8,400 meters (figure 1). 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). Leg 1 will include the deployment of a NAVOCEANO ocean glider on loan to the National Ocean Service. This arises from the low-density ocean water and sediments filling the trench. In addition to its extremely deep seafloor, 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 (Figure 2). 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. In both of these cases the driving mass has an optimum depth of about 100 km. 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. 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. Gravity anomalies and convection currents. 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. Bathymetry of the northeast corner of the Caribbean plate. The Puerto Rico Trench and the Mid-Atlantic Rise, The origin of outer topographic rises associated with trenches, Widespread occurrence of a high-velocity basal layer in the Pacific crust found with repetitive sources and sonobuoys, The structure and physical properties of the earth's crust. Click image for larger view and image credit. 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. A tilted carbonate platform provides evidence for extreme vertical tectonism in the region.This platform was horizontally deposited Plate movements have caused large magnitude earthquakes and devastating tsunamis. Large tsunamis have also hit Puerto Rico and Hispaniola, reportedly killing 1800 people in 1946 and 40 people in 1918. 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. No Derivative works - You may not alter, transform, or build upon this work. The Puerto Rico Trench is also associated with the most negative gravity anomaly on earth, -380 milliGal, which indicates the presence of an active downward force. The gravity anomaly at a location on the Earth's surface is the difference between the observed value of gravity and the value predicted by a theoretical model. Closed basins such as these are thought to document earthquake and hurricane events through the accumulation of event layers such as debris flow and turbidity current deposits and the internal deformation of deposited material. 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. Figure 4. [24], Gravity anomalies provide clues on other processes taking place deep in the lithosphere. Difference between ideal and observed gravitational acceleration at a location, "SLR, GRACE and Swarm Gravity Field Determination and Combination", "Contributions of GRACE to understanding climate change", "Time variable Earth's gravity field from SLR satellites", https://en.wikipedia.org/w/index.php?title=Gravity_anomaly&oldid=1139571563, Short description is different from Wikidata, Creative Commons Attribution-ShareAlike License 3.0, This page was last edited on 15 February 2023, at 20:17. The region has high seismicity and large earthquakes. The seabed of the Cayman Trough is flat at the segment (80.0W and 17.7N to 78.5W and 19.5N). This belt of positive anomalies is called the Outer Gravity High. Download image (jpg, 50 KB). Disclaimer
The Puerto Rico trench exhibits great water depth, extremely low gravity anomaly, and a tilted carbonate platform between (reconstructed) elevations of +1300 m and -4000 m. we suggest that these features are manifestations of large vertical movements of a segment of the Puerto Rico Trench, its forearc, and the island of Puerto Rico that took place 3.3 m.y. Newton showed that the measured value of gravity was affected by the rotation of the Earth, which caused the Earth's equator to bulge out slightly relative to its poles. Motion along its northern boundary (in the plate boundary zone region) is dominantly strike-slip (a geological fault in which an adjacent surface moves horizontally), with a small component of shortening. However, present-day slope seafloor-morphology is complicated by shaping processes, which are not readily separable through pure bathymetric analysis. 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. Seism, The fore-arc region of the northeast Caribbean plate north of Puerto Rico and the Virgin Islands has been the site of numerous seismic swarms since at least 1976. [21], Over mid-ocean ridges, the free-air anomalies are small and correlate with the ocean bottom topography. This site uses cookies. The unusually deep sea floor is not limited to the trench, but also extends farther south toward Puerto Rico. 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. The Puerto Rico trench exhibits great water depth, an extremely low gravity anomaly, and a tilted carbonate platform between (reconstructed) elevations of +1300 m and -4000 m. I argue that these features are manifestations of large vertical movements of a segment of the Puerto Rico trench, its forearc, and the island of Puerto Rico that took place 3.3 m.y. Large landslide escarpments have been mapped on the seafloor north of Puerto Rico, although their ages are unknown. Local measurements of the gravity of Earth help us to understand the planet's internal structure. 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. A positive anomaly is associated with the Ivrea body, a wedge of dense mantle rock caught up by an ancient continental collision. 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. 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). 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. 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. . 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. On this Wikipedia the language links are at the top of the page across from the article title. U.S. Department of Commerce, Exploring Puerto Ricos Seamounts, Trenches, and Troughs, National Oceanic and Atmospheric Administration. Thesis (Sc.D.) Notice, Smithsonian Terms of 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. ago over a time period as short as 14 . [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. Both terrain higher than the measurement point and valleys lower than the measurement point reduce the measured value of gravity. 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. Further refinements of the model field are usually expressed as corrections added to the measured gravity or (equivalently) subtracted from the normal gravity. 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). This shows that the low elevation of ocean basins and high elevation of continents is compensated by the thickness of the crust at depth. 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. This platform was horizontally deposited over Cretaceous to Paleocene arc rocks starting in the Late Oligocene. The Bouguer anomaly includes only the negative correction for the high terrain and so is strongly negative. 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