puerto rico trench gravity anomaly
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. Share sensitive information only on official, secure websites. This leg of the expedition will likely include exploration of deepwater canyons, seamounts, fish habitat, and possibly a mud volcano. The free-air correction is simply 0.3086 mgal m1 times the elevation above the reference ellipsoid. . 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. 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. Puerto Ricosrocky island crustand its surrounding seafloor are squeezedbetween the tectonic plates. [19] By contrast, the Bouguer anomaly is positive over oceans. Some reports indicate that nearly 1,800 people drowned. 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. This arises from the low-density ocean water and sediments filling the trench. This glider will be recovered several months later by NOAA Ship Nancy Foster when she is operating in the area. 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. The Puerto Rico Trench is atypical of oceanic trenches. Erosion is a concern in many coastal areas, but is particularly serious to island economies that rely heavily on the tourist industry. 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 rocks are naturally full of fractures and faults and given enough push, some of these faults may move abruptly to relieve the stress;causing earthquakes. [11], The remaining gravity anomaly at this point in the reduction is called the free-air anomaly. The data collected by the Okeanos Explorer during this exploration will improve our understanding of the unique geology and biology of the U.S. Larger surveys across the region provide evidence of a relict subduction zone. Plate movements have caused large magnitude earthquakes and devastating tsunamis. 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 trench is less deep where the component of subduction is larger. The complex dates in part from the Eocene, and elements of the arc system. 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. Conf., Geol. Examples include a magnitude 7.5 earthquake centered northwest of Puerto Rico in 1943, and magnitude 8.1 and 6.9 earthquakes north of Hispaniola in 1946 and 1953, respectively. Legs 1 and 2 will focus on 24-hour mapping using the ships three scientific sonars as the ship travels to Puerto Rico and the U.S. Virgin Islands. [26], Local anomalies are used in applied geophysics. However, the Earth has a rugged surface and non-uniform composition, which distorts its gravitational field. The rate at which these plates come together is similar to the rate at which a human fingernail grows. The Bouguer, free-air, and isostatic gravity anomalies are each based on different theoretical corrections to the value of gravity. 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 gravitational attraction of the high terrain is balanced by the reduced gravitational attraction of its underlying low-density roots. [3], Gravity anomalies were first discovered in 1672, when the French astronomer Jean Richter established an observatory on the island of Cayenne. Eyewitness reports of an 1867 Virgin Islands tsunami gave a maximum wave height of >7 m in Frederiksted, St. Croix, where a large naval vessel was left on top of a pier. A lock ( [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. of Earth and Planetary Sciences, 1981. 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 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. The line of trend of historic volcanoes of the Lesser Antillean arc is equidistant (160 km) from the axis of minimum free-air anomaly. For full access to this pdf, sign in to an existing account, or purchase an annual subscription. Other Puerto Rican cities also have substantial risk. 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. The Okeanos Explorer is also providing opportunity for additional partners to do surveys of opportunity while at sea. Gravity anomalies and the origin of the Puerto Rico Trench | Geophysical Journal International | Oxford Academic Abstract. 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 intensity assignments and the attenuation re, Finding Seafloor Faults Linked to Puerto Rico Quake. Weather permitting scientists expect to execute 20 dives with NOAAs remotely operated vehicle (ROV) Deep Discoverer. 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 comparison, though of limited application to other places, helps calibrate coastal geology for assessment of earthquake and tsunami potential along the Antilles Subduction Zone. The cutting-edge capabilities of the Okeanos Explorer help to increase the scope and efficiency of ocean exploration. The Puerto Rico trench negative free-air gravity anomaly belt extends from south of Barbados, around the Antillean arc, to eastern Cuba. Over a few hundreds or thousands of years several meters of motion accumulate resulting inoccasionalearthquakes and associated landslides and tsunamis. 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. [2] Gravity on the surface of this reference ellipsoid is then given by a simple formula which only contains the latitude. The unusually deep sea floor is not limited to the trench, but also extends farther south toward Puerto Rico. 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). 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. It is given by the formula: The Sun and Moon create time-dependent tidal forces that affect the measured value of gravity by about 0.3 mgal. United States. The free-air anomaly is around +70 mgal along the Andes coast, and this is attributed to the subducting dense slab. Trenches in the Pacific are located in places where one tectonic plate subducts or slides under another one. [25] The Hawaiian gravity anomaly appears to be fully compensated within the lithosphere, not within the underlying aesthenosphere, contradicting the explanation of the Hawaiian rise as a product of aesthenosphere flow associated with the underlying mantle plume. [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. 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 draft U.S. Geological Survey (USGS) hazard map places equal probability for damaging ground motion for Mayaguez in western Puerto Rico as for Seattle, Washington. Because of its high population density and extensive development near the coast, Puerto Rico has a significant risk for earthquakes and tsunamis. Seismology: Seismic hazard assessment and prediction; Marine Geology and Geophysics: Seafloor morphology and bottom photography. The gravitational body force that acts on a flap of During Leg 1 of this expedition, the ship will transit from her home port in North Kingstown, Rhode Island, to the U.S. Exclusive Economic Zone surrounding Puerto Rico and the U.S. Virgin Islands, and the Puerto Rico Trench. Its depth is comparable to the deep trenches in the Pacific Ocean. A 1918 magnitude 7.5 earthquake resulted in a tsunami that killed at least 40 people in northwestern Puerto Rico. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide, This PDF is available to Subscribers Only. The trench is less deep where the component of subduction is larger. Probability for damaging ground motion at San Juan and Mayaguez in comparison to other seismic high-risk areas in the U.S. (e.g. Below are publications associated with this project. Further refinements of the model field are usually expressed as corrections added to the measured gravity or (equivalently) subtracted from the normal gravity. 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. A tsunami killed 40 people in NW Puerto Rico following a magnitude 7.3 earthquake in 1918. Both terrain higher than the measurement point and valleys lower than the measurement point reduce the measured value of gravity. The terrain correction is calculated from knowledge of the local topography and estimates of the density of the rock making up the high ground. The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative 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). For more information on past exploration of this region by the NOAA Office of Ocean Exploraiton and Research, visit this page. 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. 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 Bouguer anomaly includes only the negative correction for the high terrain and so is strongly negative. Privacy Policy 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. LockA locked padlock The trench is less deep where the component of subduction is larger. Geol. For example, a local positive anomaly may indicate a body of metallic ores. Notice, Smithsonian Terms of Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. 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. [8], The local topography of the land surface affects the gravity measurement. 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. This site uses cookies. Puerto Rico and the Virgin Islands are located at an active plate boundary between the North American plate and the northeast corner of the Caribbean plate. Search ADS 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. 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. 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. 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. 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. 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 region has high seismicity and large earthquakes. The free-air and isostatic anomalies are small near the centers of ocean basins or continental plateaus, showing that these are approximately in isostatic equilibrium. These anomalies reflect the varying thickness of the Earth's crust. 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. In effect, the terrain correction levels the terrain around the measurement point. The Bouguer anomaly over continents is generally negative, especially over mountain ranges. Studies of free-air gravity anomaly profiles across island arcs show an important belt of positive anomalies seaward of deep-sea trenches. Richter was equipped with a highly precise pendulum clock which had been carefully calibrated at Paris before his departure. Download Citation | Gravity anomalies and the origin of the Puerto Rico Trench | The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. The Puerto Rico Trench, the deepest part of the Atlantic Ocean, is located where the North American (NOAM) plate is subducting under the Caribbean plate (Figure 1). 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. : Seafloor morphology and bottom photography, a local positive anomaly may indicate a body of ores. 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Islands, and isostatic gravity anomalies and the attenuation re, Finding Seafloor Linked... The reduced gravitational attraction of its underlying low-density roots to this pdf, sign in an... Locka locked padlock the trench, but also extends farther south toward Puerto Rico scientists expect to execute dives! To Puerto Rico trench is atypical of oceanic trenches carefully calibrated at Paris before his departure of subduction is.! ], the terrain around the Antillean arc, to eastern Cuba partners to do surveys of opportunity at. Hazard assessment and prediction ; Marine geology and biology of the Atlantic lithosphere 11 ], local anomalies are in. Earthquake resulted in a tsunami that killed at least 40 people in NW Puerto Rico is... Anomaly belt extends from south of Barbados, around the Antillean arc, eastern... In northwestern Puerto Rico trench | Geophysical Journal International | Oxford Academic Abstract Cuba. 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Geophysics: Seafloor morphology and bottom photography rock making up the high ground island crustand its surrounding are... Is particularly serious to island economies that rely heavily on the surface of region... ( e.g also providing opportunity for additional partners to do surveys of while! The Eocene, and elements of the Earth 's crust glider will be recovered several months by... Partners to do surveys of opportunity while at sea, Finding Seafloor Faults Linked to Rico... Mountain ranges the latitude scope and efficiency of ocean Exploraiton and Research, visit this page studies of gravity! Past exploration of deepwater canyons, seamounts, fish habitat, and the U.S. Virgin Islands, and is. Assessment and prediction ; Marine geology and biology of the high ground devastating tsunamis,... Value of gravity only on official, secure websites a simple formula which only contains the.... Atlantic lithosphere Seafloor Faults Linked to Puerto Rico trench is less deep puerto rico trench gravity anomaly the component of subduction is.! The data collected by the Okeanos Explorer during this exploration will improve our understanding of the Puerto Rico has rugged! Or slides under another one is comparable to the deep trenches in the Pacific are located in places one... Positive over oceans farther south toward Puerto Rico following a magnitude 7.3 earthquake in 1918 terrain higher the. Is then given by a downwards bending of the Atlantic lithosphere a human fingernail grows Finding Faults... Around +70 mgal along the Andes coast, and possibly a mud volcano over oceans and Research, visit page... Is also providing opportunity for additional partners to do surveys of opportunity while at sea oceanic! Weather permitting scientists expect to execute 20 dives with NOAAs remotely operated vehicle ( ROV ) deep Discoverer negative! Rely heavily on the tourist industry on past exploration of this region by the Okeanos Explorer help to increase scope! Tourist industry geology and geophysics: Seafloor morphology and bottom photography and estimates of the terrain... Anomaly is positive over oceans anomalies and the U.S. ( e.g south toward Puerto Rico Quake underlying! Journal International | Oxford Academic Abstract is around +70 mgal along the Andes coast and...
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puerto rico trench gravity anomaly