puerto rico trench gravity anomaly
For a measurement point above the reference ellipsoid, this means that the gravitational attraction of the bulk mass of the earth is slightly reduced. Because of its high population density and extensive development near the coast, Puerto Rico has a significant risk for earthquakes and tsunamis. 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. 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 seabed of the Cayman Trough is flat at the segment (80.0W and 17.7N to 78.5W and 19.5N). The unusually deep sea floor is not limited to the trench, but also extends farther south toward Puerto Rico. Transit line down to Puerto Rico (red line) and two survey area boxes within the region around Puerto Rico and the U.S. Virgin Islands. E-mail Updates | User Survey | Contact Us | Report Error On This Page | Privacy Policy | Disclaimer | Site Info | Site Index Abstract The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. The free-air minimum east of the Lesser Antilles is related to underthrusting of the Caribbean plate by the Atlantic Ocean plate. http://oceanexplorer.noaa.gov/explorations/03trench/trench/trench.html. Official websites use .gov Well-documented slab tears that are associated with high rates of intermediate-depth seismicity are considered here: Gibraltar arc, the southern and northern ends of the Lesser Antilles arc, and the northern end of Tonga trench. Search ADS 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). 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. 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. Different theoretical models will predict different values of gravity, and so a gravity anomaly is always specified with reference to a particular model. 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. The trench itself is very negative,[23] with values more negative than 250 mgal. Vertical motions of the Puerto Rico Trench and Puerto Rico and their cause ten Brink, Uri Abstract 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. Notice, Smithsonian Terms of A lock ( Its depth is comparable to the deep trenches in the Pacific Ocean. [20] Negative isostatic anomalies in Switzerland correlate with areas of active uplift, while positive anomalies are associated with subsidence. Subsequent cooling thickens the lithosphere again and subsidence takes place. 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. An official website of the United States government. The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. For Earth, the reference ellipsoid is the International Reference Ellipsoid, and the value of gravity predicted for points on the ellipsoid is the normal gravity, gn. However, the Earth has a rugged surface and non-uniform composition, which distorts its gravitational field. 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 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 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 ]). The region has high seismicity and large earthquakes (figure 2). [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. The gravitational body force that acts on a flap of lithosphere, hanging in the aesthenosphere and, The results of marine geophysical surveys by NOAA, Miami and the University of Durham with the Royal Navy in the eastern Caribbean region are presented as maps of the bathymetry, free-air gravity, Basalts recovered during leg 15 of the Deep Sea Drilling Project in the central Caribbean are finegrained plagioclase tholeiites which were erupted in the Late Cretaceous, at a time when North, Since the pioneering pendulum gravity measurements of Vening-Meinesz and Wright (1930) and Hess (1933, 1938), the Caribbean Sea, with its multitude of geologic problems, has received intensive study, By clicking accept or continuing to use the site, you agree to the terms outlined in our. Cayenne, being nearer the equator than Paris, would be both further from the center of Earth (reducing the Earth's bulk gravitational attraction slightly) and subject to stronger centrifugal acceleration from the Earth's rotation. 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. 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 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. Studies of free-air gravity anomaly profiles across island arcs show an important belt of positive anomalies seaward of deep-sea trenches. The geologic settings of Puerto Rico and the Virgin Islands have created or contributed to several pressing societal issues related to human safety, environmental health, and economic development. Trenches in the Pacific are located in places where one tectonic plate subducts or slides under another one. Subduction is highly oblique (10-20) to the trench axis with a large component of left-lateral strike-slip motion. The unusually deep sea floor is not limited to the trench, but also extends farther south toward Puerto Rico. 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 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. The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. Figure produced in Google Earth Pro. Large-scale gravity anomalies can be detected from space, as a by-product of satellite gravity missions, e.g., GOCE. geophys. The multi-colored lines denote the approximate locations of the EEZ boundaries. The trench is less deep where the component of subduction is larger. "Puerto Rico Trench Negative Gravity Anomaly Belt", Studies in Earth and Space Sciences, R. Shagam, R. B. Hargraves, W. J. Morgan, F. B. [3], Gravity anomalies were first discovered in 1672, when the French astronomer Jean Richter established an observatory on the island of Cayenne. 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. Large tsunamis have also hit Puerto Rico and Hispaniola, reportedly killing 1800 people in 1946 and 40 people in 1918. 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. 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). Because the island lies on an active plate boundary, earthquakes are a constant threat, and the densely populated coastal areas are vulnerable to tsunamis. 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. [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. 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. Notice, Smithsonian Terms of ) or https:// means youve safely connected to the .gov website. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide, This PDF is available to Subscribers Only. This brings the free-air anomaly, which omits the correction terms for either, close to zero. 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 Other Puerto Rican cities also have substantial risk. ago over a time period as short as 14-40 kyr. 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 sphere and cylinder sinking beneath the surface of a viscous fluid, Gravity anomalies and convection currents 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 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. Dynamically triggered offshore aftershocks, caused by passing seismic waves from main shocks located on land, are currently not considered in tsunami warnings. 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. 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. Astrophysical Observatory. A .gov website belongs to an official government organization in the United States. 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. The free-air anomaly is around +70 mgal along the Andes coast, and this is attributed to the subducting dense slab. The low-density sediments of the Molasse basin produce a negative anomaly. 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 trench is less deep where the component of subduction is larger. For example, the northeast-southwest trending high across central New Jersey represents a graben of Triassic age largely filled with dense basalts. The higher terrain is held up by the buoyancy of thicker crust "floating" on the mantle. 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 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. Other margins of the island (west, south, and south west) are also associated with massive tectonic features and may pose addtional hazard. 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. Revised December 04, 2006 by the NOAA Ocean Explorer Webmaster 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. A 1918 magnitude 7.5 earthquake resulted in a tsunami that killed at least 40 people in northwestern Puerto Rico. It is concluded that the Mohorovii discontinuity (characterized by compressional-wave velocities of about 8 km/sec) lies at 9 km. The Puerto Rico trench negative free-air gravity anomaly belt extends from south of Barbados, around the Antillean arc, to eastern Cuba. 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. The hazard from tsunamis is also apparent. 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. Click image for larger view and image credit. 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. 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. Over a few hundreds or thousands of years several meters of motion accumulate resulting inoccasionalearthquakes and associated landslides and tsunamis. Lateral variations in gravity anomalies are related to anomalous density distributions within the Earth. [26], Local anomalies are used in applied geophysics. This belt of positive anomalies is called the Outer Gravity High. Some reports indicate that nearly 1,800 people drowned. 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