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 ]). This platform was horizontally deposited over Cretaceous to Paleocene arc rocks starting in the Late Oligocene. The resulting series are then processed as if they were, Seismic-reflection profiles over the outer ridge and the Nares Basin north of Puerto Rico show that three principal structures can be traced from the north wall of the Puerto Rico Trench northward to, Seven reflection profiles over the central Aleutian trench and terrace are presented. The Bouguer anomaly over continents is generally negative, especially over mountain ranges. Figure 3. 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. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. 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). 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). ?W and trend southwestwardly toward eastern Puerto Rico. 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. ) or https:// means youve safely connected to the .gov website. The hazard from tsunamis is also apparent. Figure 1. United States. Trenches in the Pacific are located in places where one tectonic plate subducts or slides under another one. To explore along with the expedition team, visit this page. Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. Search ADS Please check your email address / username and password and try again. Correcting for these effects removed most of this anomaly. 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. 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. 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. Seismology: Seismic hazard assessment and prediction; Marine Geology and Geophysics: Seafloor morphology and bottom photography. 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. [20] Negative isostatic anomalies in Switzerland correlate with areas of active uplift, while positive anomalies are associated with subsidence. 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. 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. 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. [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. Notice, Smithsonian Terms of The result, a refinement of previous work, was, Summary 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. 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. The isostatic anomaly includes correction terms for both effects, which reduces it nearly to zero as well. However, he found that the clock ran too slowly in Cayenne, compared with the apparent motion of the stars. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide, This PDF is available to Subscribers Only. 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. The trench is less deep where the component of subduction is larger. Other Puerto Rican cities also have substantial risk.The hazard from tsunamis is also apparent. [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. Immediately after the 1946 earthquake, a tsunami struck northeastern Hispaniola and moved inland for several kilometers. Summary. The seabed of the Cayman Trough is flat at the segment (80.0W and 17.7N to 78.5W and 19.5N). Search for other works by this author on: Some aspects of the gravity field and tectonics of the northern Caribbean region, Trans, Fifth Carib. Contact Us Its profile is asymmetric: northern part is steep (about 57), southern part is about 16. The Bouguer, free-air, and isostatic gravity anomalies are each based on different theoretical corrections to the value of gravity. (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. In both of these cases the driving mass has an optimum depth of about 100 km. 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. For example, a mass of dense ore below the surface will give a positive anomaly due to the increased gravitational attraction of the ore. (or is it just me), Smithsonian Privacy Undeformed trench turbidites terminate abruptly against the inner wall which is acoustically opaque for the next, 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. No Derivative works - You may not alter, transform, or build upon this work. [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. Bathymetry of the northeast corner of the Caribbean plate. [8], The local topography of the land surface affects the gravity measurement. The free-air minimum east of the Lesser Antilles is related to underthrusting of the Caribbean plate by the Atlantic Ocean plate. A 6 month deployment of five ocean bottom seismographs recorded two such tightly clustered swarms, along with additional events. 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. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. Salt domes are typically expressed in gravity maps as lows, because salt has a low density compared to the rocks the dome intrudes. 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 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. U.S. Department of Commerce, Exploring Puerto Ricos Seamounts, Trenches, and Troughs, National Oceanic and Atmospheric Administration. The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. 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. This site uses cookies. The gravitational attraction of the high terrain is balanced by the reduced gravitational attraction of its underlying low-density roots. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. 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. The higher terrain is held up by the buoyancy of thicker crust "floating" on the mantle. 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 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. [29][30] The lowest-degree parameters, including the Earth's oblateness and geocenter motion are best determined from Satellite laser ranging.[31]. Location of earthquakes as a function of depth and size in the northeastern Caribbean. Office of Ocean Exploration and Research | National Oceanic and Atmospheric Administration | Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. 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. Seattle). Plate convergence is highly oblique (2010), resulting in a complex crustal boundary with along-strike segmentation, strain partitioning and microplate tectonics. 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. 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. Probability for damaging ground motion at San Juan and Mayaguez in comparison to other seismic high-risk areas in the U.S. (e.g. The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative ago over a time period as short as 14-40 kyr. [2] Gravity on the surface of this reference ellipsoid is then given by a simple formula which only contains the latitude. The free-air anomaly is around +70 mgal along the Andes coast, and this is attributed to the subducting dense slab. That is, the free-air anomaly is:[12], The free-air anomaly does not take into account the layer of material (after terrain leveling) outside the reference ellipsoid. 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 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. [13], The remaining gravity anomaly at this point in the reduction is called the Bouguer anomaly. The low-density sediments of the Molasse basin produce a negative anomaly. 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 correction is simply 0.3086 mgal m1 times the elevation above the reference ellipsoid. Abstract The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. These are indications of strong dynamic effects in subduction zones. The data collected by the Okeanos Explorer during this exploration will improve our understanding of the unique geology and biology of the U.S. The normal gravity accounts for the bulk gravitation of the entire Earth, corrected for its idealized shape and rotation. 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. 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. Because of its high population density and extensive development near the coast, Puerto Rico has a significant risk for earthquakes and tsunamis. 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. Lateral variations in gravity anomalies are related to anomalous density distributions within the Earth. For example, a local positive anomaly may indicate a body of metallic ores. Journal of Geophysical Research B: Solid Earth. A crustal section across the Puerto Rico trench, J. geophys. The rate at which these plates come together is similar to the rate at which a human fingernail grows. The slumped material comprises carbonate blocks, which are cohesive and the edge of the carbonate platform is steeper than most continental slopes, resulting in a higher potential runup To help understand the origin of the unusual bathymetry, gravity, and vertical tectonics of the plate boundary and to provide constraints for hazard assessment, the morphology of the entire 770-km-long trench from the Dominican Republic in the west to Anguilla in the east was mapped with multibeam echosounder during three cruises in 2002 and 2003. Thesis (Sc.D.) [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 large negative gravity anomaly is attributed to a . 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. Secure .gov websites use HTTPS The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. of Earth and Planetary Sciences, 1981. Widespread damage in Puerto Rico and Hispaniola from an earthquake in 1787 was estimated to be the result of a magnitude 8 earthquake north of the islands. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. Careful analysis of the gravity data allows geologists to make inferences about the subsurface geology. The Bouguer anomaly includes only the negative correction for the high terrain and so is strongly negative. The unusually deep sea floor is not limited to the trench and extends farther south toward Puerto Rico. [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. Click image for larger view and image credit. [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. For a measurement point above the reference ellipsoid, this means that the gravitational attraction of the bulk mass of the earth is slightly reduced. Secure .gov websites use HTTPS Bathymetry of the northeast corner of the Caribbean plate. Agreement NNX16AC86A, Is ADS down? Agreement NNX16AC86A, Journal of Geophysical Research (Solid Earth), Is ADS down? 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. [22], There are intense isostatic and free-air anomalies along island arcs. 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. Fifteen years later, Isaac Newton used his newly formulated universal theory of gravitation to explain the anomaly. 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. 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. An official website of the United States government. http://oceanexplorer.noaa.gov/explorations/03trench/trench/trench.html. Download image (jpg, 44 KB). U.S. Department of Commerce The Puerto Rico Trench is the deepest part of the Atlantic Ocean, with water depths exceeding 8,400 meters (figure 1). 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. NOTICE: This page is being retained for reference purposes only and is no longer being updated or maintained. The unusually deep sea floor is not limited to the trench, but also extends farther south toward Puerto Rico. 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 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. 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 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. Revised December 04, 2006 by the NOAA Ocean Explorer Webmaster 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. towards 2541. 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. Uri ten Brink, Chief Scientist The Puerto Rico trench negative free-air gravity anomaly belt extends from south of Barbados, around the Antillean arc, to eastern Cuba. The Caribbean plate is roughly rectangular, and it slides eastward at about 2 cm/yr relative to the North American plate. ago over a time period as short as 14 . 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