The higher terrain is held up by the buoyancy of thicker crust "floating" on the mantle. 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. For full access to this pdf, sign in to an existing account, or purchase an annual subscription. Google Scholar. (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. Larger surveys across the region provide evidence of a relict subduction zone. 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. [5], The starting point for the model field is the International Reference Ellipsoid, which gives the normal gravity gn for every point on the Earth's idealized shape. This platform was horizontally deposited over Cretaceous to Paleocene arc rocks starting in the Late Oligocene. 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. National Oceanic and Atmospheric Administration. Official websites use .gov This belt of positive anomalies is called the Outer Gravity High. Puerto Ricosrocky island crustand its surrounding seafloor are squeezedbetween the tectonic plates. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. Because the island lies on an active plate boundary, earthquakes are a constant threat, and the densely populated coastal areas are vulnerable to tsunamis. 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). Journal of Geophysical Research B: Solid Earth. 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. The Puerto Rico Trench, the deepest part of the Atlantic Ocean, is located where the North American (NOAM) plate is subducting under the Caribbean plate (Figure 1). 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. This effect is very well understood and can be calculated precisely for a given time and location using astrophysical data and formulas, to yield the tidal correction gtid. The Puerto Rico Trench is atypical of oceanic trenches. Carl Bowin, 1972. 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. A tilted carbonate platform provides evidence for extreme vertical tectonism in the region. Mo, Marine overwash from the north a few centuries ago transported hundreds of angular cobbles and boulders tens to hundreds of meters southward from limestone outcrops in the interior of Anegada, 140 km eastnortheast of Puerto Rico. [14], The isostatic anomaly is defined as the Bouger anomaly minus the gravity anomaly due to the subsurface compensation, and is a measure of the local departure from isostatic equilibrium, due to dynamic processes in the viscous mantle. 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. For example, the northeast-southwest trending high across central New Jersey represents a graben of Triassic age largely filled with dense basalts. Large-scale gravity anomalies can be detected from space, as a by-product of satellite gravity missions, e.g., GOCE. 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. The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative Immediately after the 1946 earthquake, a tsunami struck northeastern Hispaniola and moved inland for several kilometers. The free-air anomaly is also close to zero except near boundaries of crustal blocks. A lock () or https:// means youve safely connected to the .gov website. [1] 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. Erosion is a concern in many coastal areas, but is particularly serious to island economies that rely heavily on the tourist industry. Other corrections are added for various gravitational models. 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. 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. The free-air correction is simply 0.3086 mgal m1 times the elevation above the reference ellipsoid. However, the Earth has a rugged surface and non-uniform composition, which distorts its gravitational field. This takes into account the fact that the measurement is usually at a different elevation than the reference ellipsoid at the measurement latitude and longitude. 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. For example, the formation and sinking of a lithospheric root may explain negative isostatic anomalies in eastern Tien Shan. The complex dates in part from the Eocene, and elements of the arc system. Seattle). Some reports indicate that nearly 1,800 people drowned. Gravity anomalies and convection currents. Share sensitive information only on official, secure websites. The large negative gravity anomaly is attributed to a . Notice, Smithsonian Terms of 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. Official websites use .gov The overwash, after crossing a fringing coral reef and 1.5 km of shallow subtidal flats, cut dozens of breaches through sandy beach ridges, deposited a sheet of sand and shell capped with lime mud, and created inland fields of cobbles and boulders. A tilted carbonate platform provides evidence for extreme vertical tectonism in the region.This platform was horizontally deposited The Caribbean plate is roughly rectangular, and it slides eastward at about 2 cm/yr relative to the North American plate. Astrophysical Observatory. A 1918 magnitude 7.5 earthquake resulted in a tsunami that killed at least 40 people in northwestern Puerto Rico. The gravitational attraction of this layer or plate is taken into account by the Bouguer plate correction, which is 0.0419103 h mgal m2 kg1. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. Its depth is comparable to the deep trenches in the Pacific Ocean. The main topographic features of this area include: the Lesser Antilles volcanic arc, the old inactive volcanic arc of the Greater Antilles (Virgin Islands to Hispaniola), and the Caribbean and North American oceanic plates. 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 origin of the steep platform edge and the amphitheaters has been attributed to: (1) catastrophic failure, or (2) localized failures and progressive erosion. Notice, Smithsonian Terms of The unusually deep sea floor is not limited to the trench and extends farther south toward Puerto Rico. 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. At the center of a level plateau, it is approximately equal to the free air anomaly. The Puerto Rico Trench, in contrast, is situated at a boundary between two plates that The trench is shallower where the component of subduction is larger. 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. During Leg 3, encompassing most of the month of April, scientists will be exploring the U.S. 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, present-day slope seafloor-morphology is complicated by shaping processes, which are not readily separable through pure bathymetric analysis. In effect, the terrain correction levels the terrain around the measurement point. ago over a time period as short as 14-40 kyr. [24], Gravity anomalies provide clues on other processes taking place deep in the lithosphere. 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 higher continental terrain is supported by thick, low-density crust that "floats" on the denser mantle, while the ocean basins are floored by much thinner oceanic crust. 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. 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. Because the island lies on an active plate boundary, earthquakes are a constant threat, and the densely populated coastal areas are vulnerable to tsunamis. The unusually deep sea floor is not limited to the trench, but also extends farther south toward Puerto Rico. 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. Please check your email address / username and password and try again. This glider will be recovered several months later by NOAA Ship Nancy Foster when she is operating in the area. Crossref. National Oceanic and Atmospheric Administration 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. These anomalies reflect the varying thickness of the Earth's crust. This site uses cookies. You do not have access to this content, please speak to your institutional administrator if you feel you should have access. 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. Viscous fluid model estimates of crustal thickness and free-air anomaly compared with measured free- air anomalies and seismic depths of Puerto Rico trench and mid-Atlantic rise Document ID 19660037496 Document Type 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. 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 cutting-edge capabilities of the Okeanos Explorer help to increase the scope and efficiency of ocean exploration. Uri ten Brink, Chief Scientist We document the spatial and temporal variability of. The risk to life and economic infrastructure is significant due to the fact that over 3 million U.S. citizens live along the coastlines of Puerto Rico and the Virgin Islands. A .gov website belongs to an official government organization in the United States. The frequency of occurrence of earthquakes with different seismic moments is expressed in terms of the rate of slip on a fault and to the largest seismic moment likely to occur in the region. 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. For more information on past exploration of this region by the NOAA Office of Ocean Exploraiton and Research, visit this page. Search ADS Agreement NNX16AC86A, Is ADS down? Lateral variations in gravity anomalies are related to anomalous density distributions within the Earth. The Puerto Rico trench negative free-air gravity anomaly belt extends from south of Barbados, around the Antillean arc, to eastern Cuba. [1] Typically the model is based on simplifying assumptions, such as that, under its self-gravitation and rotational motion, the planet assumes the figure of an ellipsoid of revolution. ago over a time period as short as 14-40 kyr. [27], At scales between entire mountain ranges and ore bodies, Bouguer anomalies may indicate rock types. Note that the Puerto Rico Trench, a deep trough where the North American plate slides past and underneath the Antilles, becomes deeper and wider north of Puerto Rico. 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. geophys. This belt of positive anomalies is called the, Gravity models of oceanic trenches computed prior to the advent of plate tectonic concepts fell into two classes of solutions: (1) if a homogeneous mantle density was assumed, then the gravity models, The free air gravity anomaly and depth are sampled at 2-km intervals along two long, reasonably straight ship tracks across the Atlantic Ocean. The gravitational body force that acts on a flap of lithosphere, hanging in the aesthenosphere and, The authors propose that the Caribbean (Ca)-North American (NA) plate boundary zone (pbz) from the Puerto Rico Trench to the Venezuelan Basin from Mona Canyon east has been in left-transtension over, Summary. Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. Figure 3. Despite the potential for these features to contain valuable and vulnerable ocean resources, very little is known about them, making this an important area to map and explore. This will be the first Okeanos Explorer cruise to plan on conducting ROV operations 12 hours a day. A tsunami killed 40 people in NW Puerto Rico following a magnitude 7.3 earthquake in 1918. Download image (jpg, 50 KB). 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. of Earth and Planetary Sciences, 1981. 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. Subsequent cooling thickens the lithosphere again and subsidence takes place. subducts, or slides, under another one. This new type of lander will likely provide the first full-depth CTD measurements in the Puerto Rico Trench. 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. 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. 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 (figure 1). An official government organization in the area trench and extends farther south Puerto... Pdf, sign in to an official government organization in the United States a rugged puerto rico trench gravity anomaly! 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