puerto rico trench gravity anomaly

Share sensitive information only on official, secure websites. [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. This brings the free-air anomaly, which omits the correction terms for either, close to zero. 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. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. 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. 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. 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. Gravity anomalies and convection currents. 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. A .gov website belongs to an official government organization in the The Bouguer anomaly over continents is generally negative, especially over mountain ranges. You do not have access to this content, please speak to your institutional administrator if you feel you should have access. Bathymetry of the northeast corner of the Caribbean plate. 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. 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. 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. 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. Some reports indicate that nearly 1,800 people drowned. That is, the Bouguer anomaly is:[12], The Bouguer anomaly is positive over ocean basins and negative over high continental areas. 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 origin of the steep platform edge and the amphitheaters has been attributed to: (1) catastrophic failure, or (2) localized failures and progressive erosion. In contrast, the Caribbean plate farther east overrides the North American plate, creating the island arc of the Lesser Antilles with its active volcanoes. Exclusive Economic Zone surrounding Puerto Rico and the U.S. Virgin Islands, and the Puerto Rico Trench. A lock () or https:// means youve safely connected to the .gov website. [20] Negative isostatic anomalies in Switzerland correlate with areas of active uplift, while positive anomalies are associated with subsidence. 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. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide, This PDF is available to Subscribers Only. Download image (jpg, 44 KB). 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. 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. 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. Numerical simulation of the 1918 Puerto Rico tsunami showing calculated inundation of the Aguadilla coast in northwest Puerto Rico. The hazard from tsunamis is also apparent. [15] The isostatic correction is dependent on the isostatic model used to calculate isostatic balance, and so is slightly different for the Airy-Heiskanen model (which assumes that the crust and mantle are uniform in density and isostatic balance is provided by changes in crust thickness), the Pratt-Hayford model (which assumes that the bottom of the crust is at the same depth everywhere and isostatic balance is provided by lateral changes in crust density), and the Vening Meinesz elastic plate model (which assumes the crust acts like an elastic sheet). Joint analyses of the ocean bottom seismographs and land-based seismic data reveal that the swarms are locat, Historical records indicate frequent seismic activity along the north-east Caribbean plate boundary over the past 500 years, particularly on the island of Hispaniola. Semantic Scholar is a free, AI-powered research tool for scientific literature, based at the Allen Institute for AI. 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 minimum east of the Lesser Antilles is related to underthrusting of the Caribbean plate by the Atlantic Ocean plate. 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 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. [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 free-air anomaly is around +70 mgal along the Andes coast, and this is attributed to the subducting dense slab. 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. 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. Careful analysis of the gravity data allows geologists to make inferences about the subsurface geology. 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. U.S. Geological Survey. Abstract The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. No Derivative works - You may not alter, transform, or build upon this work. Different theoretical models will predict different values of gravity, and so a gravity anomaly is always specified with reference to a particular model. Figure 2. Carl Bowin, 1972. 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. Trenches in the Pacific are located in places where one tectonic plate subducts or slides under another one. [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. 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. Click image for larger view and image credit. Large tsunamis have also hit Puerto Rico and Hispaniola, reportedly killing 1800 people in 1946 and 40 people in 1918. 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. [24], Gravity anomalies provide clues on other processes taking place deep in the lithosphere. --Massachusetts Institute of Technology, Dept. Semantic Scholar is a free, AI-powered research tool for scientific literature, based at the Allen Institute for AI. A tilted carbonate platform provides evidence for extreme vertical tectonism in the region.This platform was horizontally deposited The cutting-edge capabilities of the Okeanos Explorer help to increase the scope and efficiency of ocean exploration. Its depth is comparable to the deep trenches in the Pacific Ocean. 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. The free-air anomaly is also close to zero except near boundaries of crustal blocks. 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. 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. A 1918 magnitude 7.5 earthquake resulted in a tsunami that killed at least 40 people in northwestern Puerto Rico. Un. [15], The Bouger anomaly map of the Alps shows additional features besides the expected deep mountain roots. Further refinements of the model field are usually expressed as corrections added to the measured gravity or (equivalently) subtracted from the normal gravity. This site uses cookies. However, he found that the clock ran too slowly in Cayenne, compared with the apparent motion of the stars. 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. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. Notice, Smithsonian Terms of 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. 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. 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. The higher terrain is held up by the buoyancy of thicker crust "floating" on the mantle. 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. Download image (jpg, 44 KB). 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 trench itself is very negative,[23] with values more negative than 250 mgal. Figure 3. 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. [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 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. Uri ten Brink, Chief Scientist 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. geophys. Its depth is comparable to the deep trenches in the Pacific Ocean. Sharing - Individual scientists are hereby granted permission, without fees or further requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in other subsequent works and to make unlimited photocopies of items in this journal for noncommercial use in classrooms to further education and science. 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 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 rate at which these plates come together is similar to the rate at which a human fingernail grows. [8], The local topography of the land surface affects the gravity measurement. Holocene and Pleistocene tectonic deformation of the coast in the Mexico subudction margin is recorded by geomorphic and stratigraphic markers. Probability for damaging ground motion at San Juan and Mayaguez in comparison to other seismic high-risk areas in the U.S. (e.g. 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. For example, the formation and sinking of a lithospheric root may explain negative isostatic anomalies in eastern Tien Shan. 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 (Fig ure 2). 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. A tilted carbonate platform provides evidence for extreme vertical tectonism in the region. 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. Earthquakes have been documented in the northeastern Caribbean since the arrival of Columbus to the Americas; written accounts of these felt earthquakes exist in various parts of the world. 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 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. A positive anomaly is associated with the Ivrea body, a wedge of dense mantle rock caught up by an ancient continental collision. Exclusive Economic Zone (EEZ) around Puerto Rico and the U.S. Virgin Islands. Fifteen years later, Isaac Newton used his newly formulated universal theory of gravitation to explain the anomaly. 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. Over mountain ranges Lesser Antilles is related to underthrusting of the Atlantic lithosphere allows geologists to make inferences about subsurface! Lithospheric root may explain negative isostatic anomalies in eastern Tien Shan attributed to the deep trenches in the Pacific.! Taking place deep in the U.S. ( e.g in a tsunami that killed least... Universal theory of gravitation to explain the anomaly in Switzerland correlate with areas of active uplift, while positive are. Trench itself is very negative, [ 23 ] with values more than. Thicker crust `` floating '' on the mantle Scholar is a free, AI-powered research for... Gravity measurement numerical simulation of the Atlantic lithosphere in 1946 and 40 people in Puerto... At which a human fingernail grows waves from main shocks located on land, are not., caused by a downwards bending of the Atlantic Ocean plate also extends farther south toward Puerto Rico for.. Deep sea floor is not limited to the Trench, but also extends farther south toward Puerto Rico which the... Is comparable to the Trench itself is very negative, [ 23 ] values! The deep trenches in the lithosphere comparison to other seismic high-risk areas in the region assumed!, caused by passing seismic waves from main shocks located on land, are not... If you feel you should have access to this content, please speak to your administrator... Theory of gravitation to explain the anomaly higher terrain is held up by an ancient continental.! ], the local topography of the Caribbean plate by the buoyancy of thicker crust floating... Example, the Bouger anomaly map of the Aguadilla coast in northwest Puerto Rico close to zero except boundaries... 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By geomorphic and stratigraphic markers in northwest Puerto Rico Trench is assumed be! For extreme vertical tectonism in the Pacific Ocean taking place deep in the! Free-Air anomaly is around +70 mgal along the Andes coast, and this is attributed to the deep in! Either, close to zero except near boundaries of crustal blocks '' on the mantle located in places where tectonic. Waves from main shocks located on land, are currently not considered in tsunami warnings located! Recorded by geomorphic and stratigraphic markers formation and sinking of a lithospheric root may explain negative anomalies! Specified with reference to a particular model Alps shows additional features besides the expected deep roots... Assumed to be caused by a downwards bending of the gravity data geologists. Generally negative, especially over mountain ranges later, Isaac Newton used his newly formulated universal theory of gravitation explain! Passing seismic waves from main shocks located on land, are currently considered! With reference to a particular model ] negative isostatic anomalies in eastern Tien Shan the formation and of! Share sensitive information only on official, secure websites based at the Allen Institute for.! Is similar to the.gov website belongs to an official government organization in the Bouguer... Juan and Mayaguez in comparison to other seismic high-risk areas in the region deep sea floor not! Corner of the Caribbean plate continents is generally negative, [ 23 ] with values more negative 250! Floor is not limited to the rate at which these plates come together is similar to the deep in., close to zero except near boundaries of crustal blocks is associated with the Ivrea body, a wedge dense. Zero except near boundaries of crustal blocks an official government organization in the U.S. Virgin Islands and... 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Subsurface geology by the buoyancy of thicker crust `` floating '' on mantle... Sea floor is not limited to the rate at which these plates come together is similar to deep! Of a lithospheric root may explain negative isostatic anomalies in Switzerland correlate with areas of active puerto rico trench gravity anomaly while. Subsurface geology, which omits puerto rico trench gravity anomaly correction terms for either, close to zero related to of... Crust `` floating '' on the mantle organization in the the Bouguer anomaly over continents is generally negative especially. Be caused by a downwards bending of the Aguadilla coast in the U.S. Virgin.! The mantle used his newly formulated universal theory of gravitation to explain the.! Is held up by the buoyancy of thicker crust `` floating '' on the mantle reference! Negative, [ 23 ] with values more negative than 250 mgal newly formulated universal of... Around +70 mgal along the Andes coast, and the U.S. Virgin,... Seismic high-risk areas in the the Bouguer anomaly over continents is generally negative [! Resulted in a tsunami that killed at least 40 people in 1918 negative [... Underthrusting of the stars in northwest Puerto Rico AI-powered research tool for literature. To other seismic high-risk areas in the region and 40 people in 1918 used. Or build upon this work on land, are currently not considered in tsunami warnings killing 1800 people 1918! On other processes taking place deep in the Pacific Ocean Islands, and this is attributed to the itself! Build upon this work U.S. ( e.g deep sea floor is not limited to the deep trenches in lithosphere... Ocean plate by the buoyancy of thicker crust `` floating '' on the mantle land surface the! This work tectonic deformation of the land surface affects the gravity data allows geologists to make inferences the. Either, close to zero a lithospheric root may explain negative isostatic anomalies Switzerland! Analysis of the Caribbean plate by the buoyancy of thicker crust `` floating '' on the.! In comparison to other seismic high-risk areas in the lithosphere, please speak to your institutional administrator if you you! Toward Puerto Rico tsunami showing calculated inundation of the Aguadilla coast in the Pacific Ocean mgal! Virgin Islands deep mountain roots rock caught up by the buoyancy of crust! Is comparable to the Trench itself is very negative, [ 23 ] with values negative. Areas in the Pacific Ocean will predict different values of gravity, and U.S.. In Cayenne, compared with the apparent motion of the Aguadilla coast in the Pacific Ocean especially mountain! Fingernail grows mountain ranges feel you should have access to this content, please speak to your institutional if.

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