puerto rico trench gravity anomaly
Simple Bouguer gravity anomalies onshore were reduced to a sea level datum. 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. Seismology: Seismic hazard assessment and prediction; Marine Geology and Geophysics: Seafloor morphology and bottom photography. 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. Some reports indicate that nearly 1,800 people drowned. The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. 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. Use, Smithsonian Different theoretical models will predict different values of gravity, and so a gravity anomaly is always specified with reference to a particular model. 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. This is taken into account by the terrain correction gT. These are indications of strong dynamic effects in subduction zones. 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. In the 20th century alone there have been several very large earthquakes north of Puerto Rico (Ms 7.3 in 1918; Ms 7.8 in 1943; Ms 8.0 in 1946 and four major aftershocks of Ms 7.6, 7.0, 7.3, 7.1 between 1946 and 1953). [19] By contrast, the Bouguer anomaly is positive over oceans. 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. A tilted carbonate platform provides evidence for extreme vertical tectonism in the region.This platform was horizontally deposited Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. 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 unusually deep sea floor is not limited to the trench, but also extends farther south toward Puerto Rico. 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 seabed of the Cayman Trough is flat at the segment (80.0W and 17.7N to 78.5W and 19.5N). 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. This site uses cookies. Further refinements of the model field are usually expressed as corrections added to the measured gravity or (equivalently) subtracted from the normal gravity. Click image for larger view and image credit. Some reports indicate that nearly 1,800 people drowned. Trenches in the Pacific are located in places where one tectonic plate subducts or slides under another one. [20] Negative isostatic anomalies in Switzerland correlate with areas of active uplift, while positive anomalies are associated with subsidence. Gravity anomalies are modelled assuming that the crustal thicknesses of the Atlantic and Caribbean Oceans are constant (but different . Click image for larger view and image credit. 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 ]). Privacy Policy geophys. A positive anomaly is associated with the Ivrea body, a wedge of dense mantle rock caught up by an ancient continental collision. [21], Over mid-ocean ridges, the free-air anomalies are small and correlate with the ocean bottom topography. The rise may instead be a result of lithosphere thinning: The underlying aesthenosphere is less dense than the lithosphere and it rises to produce the swell. This comparison, though of limited application to other places, helps calibrate coastal geology for assessment of earthquake and tsunami potential along the Antilles Subduction Zone. Its depth is comparable to the deep trenches in the Pacific Ocean. 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. Nevertheless, a tsunami recorded on a Caribbean Deep-Ocean Assessment and Reporting of Tsunami (D, The North American (NOAM) plate converges with the Caribbean (CARIB) plate at a rate of 20.00.4mm/yr. Studies of free-air gravity anomaly profiles across island arcs show an important belt of positive anomalies seaward of deep-sea trenches. This new type of lander will likely provide the first full-depth CTD measurements in the Puerto Rico Trench. [18], More generally, the Airy isostatic anomaly is zero over regions where there is complete isostatic compensation. Dynamically triggered offshore aftershocks, caused by passing seismic waves from main shocks located on land, are currently not considered in tsunami warnings. [11], The remaining gravity anomaly at this point in the reduction is called the free-air anomaly. [3], Gravity anomalies were first discovered in 1672, when the French astronomer Jean Richter established an observatory on the island of Cayenne. [15], The Bouger anomaly map of the Alps shows additional features besides the expected deep mountain roots. 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. 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 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. The hazard from tsunamis is also apparent. (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. Correcting for these effects removed most of this anomaly. This gravity anomaly can reveal the presence of subsurface structures of unusual density. Disclaimer Journal of Geophysical Research B: Solid Earth. Google Scholar. Geol. 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. 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 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. The normal gravity accounts for the bulk gravitation of the entire Earth, corrected for its idealized shape and rotation. 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. We examined two of several cobble and boulder fields as part of an effort to interpret whether the overwash resulted from a tsunami or a storm in a location where both e, 12201 Sunrise Valley Drive Reston, VA 20192, Region 2: South Atlantic-Gulf (Includes Puerto Rico and the U.S. Virgin Islands), Region 12: Pacific Islands (American Samoa, Hawaii, Guam, Commonwealth of the Northern Mariana Islands), Woods Hole Coastal and Marine Science Center, Significant Earthquakes on a major fault system in Hispaniola, Puerto Rico, the Virgin Islands, and the Lesser Antilles, 15002010: Implications for Seismic Hazard, Coastal and Marine Hazards and Resources Program, Caribbean Tsunami and Earthquake Hazards Studies- Models, Caribbean Tsunami and Earthquake Hazards Studies- Stress Changes and Earthquake Hazard, Caribbean Tsunami and Earthquake Hazards Studies-Tsunami Potential, Caribbean Tsunami and Earthquake Hazards Studies- Seafloor Map, Mysterious tsunami in the Caribbean Sea following the 2010 Haiti earthquake possibly generated by dynamically triggered early aftershocks, Along-strike segmentation in the northern Caribbean plate boundary zone (Hispaniola sector): Tectonic implications, Semi-automated bathymetric spectral decomposition delineates the impact of mass wasting on the morphological evolution of the continental slope, offshore Israel, Effects of 2010 Hurricane Earl amidst geologic evidence for greater overwash at Anegada, British Virgin Islands, Event sedimentation in low-latitude deep-water carbonate basins, Anegada passage, northeast Caribbean, Slope failures and timing of turbidity flows north of Puerto Rico, Seismic hazard from the Hispaniola subduction zone: correction to "Historical perspective on seismic hazard to Hispaniola and the northeast Caribbean region", Slab tears and intermediate-depth seismicity, Seismic evidence for a slab tear at the Puerto Rico Trench, Reply to a comment by Carol S. Prentice, Paul Mann, and Luis R. Pea on: "Historical perspective on seismic hazard to Hispaniola and the northeast Caribbean region" by U. ten Brink et al. Determining wh, Waters from the Atlantic Ocean washed southward across parts of Anegada, east-northeast of Puerto Rico, during a singular event a few centuries ago. 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 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. [27], At scales between entire mountain ranges and ore bodies, Bouguer anomalies may indicate rock types. 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. ?W and trend southwestwardly toward eastern Puerto Rico. Over four million U.S. citizens live on these islands, mostly along the coast. 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. On this Wikipedia the language links are at the top of the page across from the article title. Erosion is a concern in many coastal areas, but is particularly serious to island economies that rely heavily on the tourist industry. Secure .gov websites use HTTPS 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. 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 ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative A crustal section across the Puerto Rico trench, J. geophys. Bull. Because the island lies on an active plate boundary, earthquakes are a constant threat, and the densely populated coastal areas are vulnerable to tsunamis. [8], The local topography of the land surface affects the gravity measurement. The trench is less deep where the component of subduction is larger. The residual gravity anomalies are then consistent with the existence of a subcrustal dense mass, that could be the hanging slab of lithosphere. U.S. Department of Commerce, Exploring Puerto Ricos Seamounts, Trenches, and Troughs, National Oceanic and Atmospheric Administration. 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, a mass of dense ore below the surface will give a positive anomaly due to the increased gravitational attraction of the ore. Because of its high population density and extensive development near the coast, Puerto Rico has a significant risk for earthquakes and tsunamis. Semantic Scholar is a free, AI-powered research tool for scientific literature, based at the Allen Institute for AI. 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. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. The data collected by the Okeanos Explorer during this exploration will improve our understanding of the unique geology and biology of the U.S. A 6 month deployment of five ocean bottom seismographs recorded two such tightly clustered swarms, along with additional events. Contact Us The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. This arises from the low-density ocean water and sediments filling the trench. Motion along its northern boundary (in the plate boundary zone region) is dominantly strike-slip (a geological fault in which an adjacent surface moves horizontally), with a small component of shortening. 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. 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. 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). 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. A sphere and cylinder sinking beneath the surface of a viscous fluid, Gravity anomalies and convection currents 2. The rate at which these plates come together is similar to the rate at which a human fingernail grows. 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. 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. This is consistent with seismic data and suggests the presence of a low-density magma chamber under the ridge axis. The free-air correction is simply 0.3086 mgal m1 times the elevation above the reference ellipsoid. Below are other science projects associated with this project. 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