puerto rico trench gravity anomaly
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. 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. Noncommercial - you may not use this work for commercial purpose. 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. Over a few hundreds or thousands of years several meters of motion accumulate resulting inoccasionalearthquakes and associated landslides and tsunamis. 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. [2] Gravity on the surface of this reference ellipsoid is then given by a simple formula which only contains the latitude. Agreement NNX16AC86A, Journal of Geophysical Research (Solid Earth), Is ADS down? A tilted carbonate platform provides evidence for extreme vertical tectonism in the region. In contrast, the Caribbean plate farther east overrides the North American plate, creating the island arc of the Lesser Antilles with its active volcanoes. We explore the interaction between thrust events on the subduction interface and strike-slip faults within the forearc region using 3-D models of static Coulomb stress change. 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. The difference between the corrected measured gravity and the normal gravity is the gravity anomaly.[6]. 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 tsunami killed 40 people in NW Puerto Rico following a magnitude 7.3 earthquake in 1918. NOTICE: This page is being retained for reference purposes only and is no longer being updated or maintained. 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. 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 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. This shows that the low elevation of ocean basins and high elevation of continents is compensated by the thickness of the crust at depth. Notice, Smithsonian Terms of Site Info, NOAA Ocean Exploration The unusually deep sea floor is not limited to the trench and extends farther south toward Puerto Rico. This study aims to explore the utility of bathymetric spectral decomposition in order to separate and char, The submerged carbonate platform north of Puerto Rico terminates in a high (3,0004,000 m) and in places steep (>45) slope characterized by numerous landslide scarps including two 3050 km-wide amphitheater-shaped features. A 6 month deployment of five ocean bottom seismographs recorded two such tightly clustered swarms, along with additional events. 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. Lateral variations in gravity anomalies are related to anomalous density distributions within the Earth. The unusually deep sea floor is not limited to the trench, but also extends farther south toward 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 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 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. Below are other science projects associated with this project. The Puerto Rico Trench is the deepest part of the Atlantic Ocean, with water depths exceeding 8,300 meters. 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. Gravity anomalies and convection currents. Bathymetry of the northeast corner of the Caribbean plate. 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. 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. Some reports indicate that nearly 1,800 people drowned. 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. 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. 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. Exclusive Economic Zone (EEZ) around Puerto Rico and the U.S. Virgin Islands. Studies of free-air gravity anomaly profiles across island arcs show an important belt of positive anomalies seaward of deep-sea trenches. [11], The remaining gravity anomaly at this point in the reduction is called the free-air anomaly. 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. Immediately after the 1946 earthquake, a tsunami struck northeastern Hispaniola and moved inland for several kilometers. Google Scholar. Large landslide escarpments have been mapped on the seafloor north of Puerto Rico, although their ages are unknown. 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. However, the Earth has a rugged surface and non-uniform composition, which distorts its gravitational field. Image courtesy of the NOAA Office of Ocean Exploration and Research. The ridge and its flanks appear to be fully isostatically compensated. Different theoretical models will predict different values of gravity, and so a gravity anomaly is always specified with reference to a particular model. An official website of the United States government. 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. For example, a local positive anomaly may indicate a body of metallic ores. 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. This will be the first Okeanos Explorer cruise to plan on conducting ROV operations 12 hours a day. The region has high seismicity and large earthquakes (figure 2). [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. 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. 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. Abstract The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. The Okeanos Explorer is also providing opportunity for additional partners to do surveys of opportunity while at sea. 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. The rate at which these plates come together is similar to the rate at which a human fingernail grows. [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. (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. Privacy Policy Van Houten, C. A. Burk, H. D. Holland, L. C. Hollister. The region has high seismicity and large earthquakes. 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). [8], The local topography of the land surface affects the gravity measurement. Its profile is asymmetric: northern part is steep (about 57), southern part is about 16. Because the island lies on an active plate boundary, earthquakes are a constant threat, and the densely populated coastal areas are vulnerable to tsunamis (Uri ten Brink, 2003). 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. ) or https:// means youve safely connected to the .gov website. It is concluded that the Mohorovii discontinuity (characterized by compressional-wave velocities of about 8 km/sec) lies at 9 km. An official website of the United States government. 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. For more information on past exploration of this region by the NOAA Office of Ocean Exploraiton and Research, visit this page. Plate movements have caused large magnitude earthquakes and devastating tsunamis. 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. The unusually deep sea floor is not limited to the trench, but also extends farther south toward Puerto Rico. 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. Dynamically triggered offshore aftershocks, caused by passing seismic waves from main shocks located on land, are currently not considered in tsunami warnings. The free-air correction is simply 0.3086 mgal m1 times the elevation above the reference ellipsoid. 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. [24], Gravity anomalies provide clues on other processes taking place deep in the lithosphere. 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. Leg 1 will include the deployment of a NAVOCEANO ocean glider on loan to the National Ocean Service. Please check your email address / username and password and try again. 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. 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