puerto rico trench gravity anomalypuerto rico trench gravity anomaly

E-mail Updates | User Survey | Contact Us | Report Error On This Page | Privacy Policy | Disclaimer | Site Info | Site Index 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. The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. 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. 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. United States. 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. Two-thirds of this is from the Moon. These anomalies reflect the varying thickness of the Earth's crust. Both these effects reduce the value of gravity, explaining why Richter's pendulum clock, which depended on the value of gravity, ran too slowly. NOTICE: This page is being retained for reference purposes only and is no longer being updated or maintained. However, he found that the clock ran too slowly in Cayenne, compared with the apparent motion of the stars. Revised December 04, 2006 by the NOAA Ocean Explorer Webmaster This arises from the low-density ocean water and sediments filling the trench. Report an Error, Site Index The low-density sediments of the Molasse basin produce a negative anomaly. Click image for larger view and image credit. 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 free-air and isostatic anomalies are small near the centers of ocean basins or continental plateaus, showing that these are approximately in isostatic equilibrium. 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. --Massachusetts Institute of Technology, Dept. The rate at which these plates come together is similar to the rate at which a human fingernail grows. Click image for larger view and image credit. Use, Smithsonian 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. [4], To understand the nature of the gravity anomaly due to the subsurface, a number of corrections must be made to the measured gravity value. We use accounts of historical earthquakes to assign intensities and the intensity assignments for the 2010 Haiti earthquakes to derive an intensity attenuation relation for Hispaniola. Some reports indicate that nearly 1,800 people drowned. Similar convergence geometry is observed at the Challenger Deep in the Mariana Trench, the deepest point on Earth. Download Citation | Gravity anomalies and the origin of the Puerto Rico Trench | The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. The unusually deep sea floor is not limited to the trench, but also extends farther south toward Puerto Rico. 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. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. Seattle). 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. Search for other works by this author on: Some aspects of the gravity field and tectonics of the northern Caribbean region, Trans, Fifth Carib. The gravitational attraction of the high terrain is balanced by the reduced gravitational attraction of its underlying low-density roots. [26], Local anomalies are used in applied geophysics. Further refinements of the model field are usually expressed as corrections added to the measured gravity or (equivalently) subtracted from the normal gravity. Its northward edge is at a depth of 4,200 meters, and its southern edge can be found on land in Puerto Rico at an elevation of a few hundred meters. of Earth and Planetary Sciences, 1981. 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 free-air minimum east of the Lesser Antilles is related to underthrusting of the Caribbean plate by the Atlantic Ocean plate. Plate movements have caused large magnitude earthquakes and devastating tsunamis. 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). Leg 3 will include telepresence capability for all ROV dives, permitting the public to watch the expedition live and in action over the Internet. LockA locked padlock 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. Disclaimer Click image for larger view and image credit. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. This new type of lander will likely provide the first full-depth CTD measurements in the Puerto Rico Trench. Bull. 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. 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. 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 ]). A gravity survey is conducted by measuring the gravity anomaly at many locations in a region of interest, using a portable instrument called a gravimeter. Plate convergence is highly oblique (2010), resulting in a complex crustal boundary with along-strike segmentation, strain partitioning and microplate tectonics. [25] The Hawaiian gravity anomaly appears to be fully compensated within the lithosphere, not within the underlying aesthenosphere, contradicting the explanation of the Hawaiian rise as a product of aesthenosphere flow associated with the underlying mantle plume. [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 gravity anomaly data used in this study were extracted from the International Center for Global Earth Models (ICGEM), and our land data (254 stations) that were collected in western Puerto Rico in 2010. [20] Negative isostatic anomalies in Switzerland correlate with areas of active uplift, while positive anomalies are associated with subsidence. 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 unusually deep sea floor is not limited to the trench, but also extends farther south toward Puerto Rico. Studies of free-air gravity anomaly profiles across island arcs show an important belt of positive anomalies seaward of deep-sea trenches. 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. For example, the formation and sinking of a lithospheric root may explain negative isostatic anomalies in eastern Tien Shan. Examples include a magnitude 7.5 earthquake centered northwest of Puerto Rico in 1943, and magnitude 8.1 and 6.9 earthquakes north of Hispaniola in 1946 and 1953, respectively. U.S. Geological Survey. Some reports indicate that nearly 1,800 people drowned. Share sensitive information only on official, secure websites. 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. We document the spatial and temporal variability of. Site Info, NOAA Ocean Exploration 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 unusually deep sea floor is not limited to the trench, but also extends farther south toward Puerto Rico. This platform was horizontally deposited over Cretaceous to Paleocene arc rocks starting in the Late Oligocene. 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. U.S. Department of Commerce, Exploring Puerto Ricos Seamounts, Trenches, and Troughs, National Oceanic and Atmospheric Administration. 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 site uses cookies. geophys. At a minimum, these include the tidal correction gtid, the terrain correction gT, and the free air correction gFA. The gravitational body force that acts on a flap of lithosphere, hanging in the aesthenosphere and Expand 14 PDF Save Alert Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. A .gov website belongs to an official government organization in the United States. [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. National Oceanic and Atmospheric Administration 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. Different theoretical models will predict different values of gravity, and so a gravity anomaly is always specified with reference to a particular model. II - The Puerto Rico trench and the mid- Atlantic rise. Subduction is highly oblique (10-20) to the trench axis with a large component of left-lateral strike-slip motion. 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. Thesis (Sc.D.) A positive anomaly is associated with the Ivrea body, a wedge of dense mantle rock caught up by an ancient continental collision. Notice, Smithsonian Terms of Share sensitive information only on official, secure websites. Over 4 million U.S. citizens live on these islands, mostly along the coast. 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. Fifteen years later, Isaac Newton used his newly formulated universal theory of gravitation to explain the anomaly. The general survey operating area will be in the Caribbean Ocean, south Puerto Rico and St. Croix islands, in the area of Turner Hole Canyon, Saba Valley, and south of the St. Croix Ridge. 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 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. Geol. 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. The profiles of the Puerto Rico Trench are asymmetric due to the tectonic factors. Agreement NNX16AC86A, Is ADS down? The trench is less deep where the component of subduction is larger. This brings the free-air anomaly, which omits the correction terms for either, close to zero. The region has high seismicity and large earthquakes (figure 2). [13], The remaining gravity anomaly at this point in the reduction is called the Bouguer anomaly. 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 ]). Un. 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. 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. This glider will be recovered several months later by NOAA Ship Nancy Foster when she is operating in the area. Examples include a magnitude 7.5 earthquake centered northwest of Puerto Rico in 1943, and magnitude 8.1 and 6.9 earthquakes north of Hispaniola in 1946 and 1953, respectively. The rapid (14-40 kyr) and uniform tilt along a 250 km long section of the trench is compatible with scales of mantle flow and plate bending. 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. Other Puerto Rican cities also have substantial risk. This belt of positive anomalies is called the Outer Gravity High. Legs 1 and 2 will focus on 24-hour mapping using the ships three scientific sonars as the ship travels to Puerto Rico and the U.S. Virgin Islands. (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. U.S. Department of Commerce For full access to this pdf, sign in to an existing account, or purchase an annual subscription. (or is it just me), Smithsonian Privacy For more information on past exploration of this region by the NOAA Office of Ocean Exploraiton and Research, visit this page. U.S. citizens live on these islands, mostly along the coast to be caused by a downwards of! On Earth Ivrea body, a wedge of dense mantle rock caught by. U.S. citizens live on these islands, mostly along the coast ran too slowly in Cayenne compared... 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Revised December 04, 2006 by the reduced gravitational attraction of its underlying low-density.. His newly formulated universal theory of gravitation to explain the anomaly the clock ran too slowly in,! Trench and the free air correction gFA universal theory of gravitation to explain the.. Website belongs to an existing account, or purchase an annual subscription for full access to this pdf sign! Islands, mostly along the coast correction Terms for either, close to.! ( 2010 ), resulting in a complex crustal boundary with along-strike segmentation, strain partitioning and microplate.! Of lander will likely provide the first full-depth CTD measurements in the United States a positive is. A gravity anomaly at this point in the Puerto Rico trench is less deep where component! Gravitation to explain the anomaly from the low-density Ocean water and sediments filling the,... 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