The free-air minimum east of the Lesser Antilles is related to underthrusting of the Caribbean plate by the Atlantic Ocean plate. 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. LockA locked padlock 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. 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. 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. Figure 4. Because of its high population density and extensive development near the coast, Puerto Rico has a significant risk for earthquakes and tsunamis. 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 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. With the exception of the alkali basalts of Grenada, the volcanics of the arc can, The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. The residual gravity anomalies are then consistent with the existence of a subcrustal dense mass, that could be the hanging slab of lithosphere. [27], At scales between entire mountain ranges and ore bodies, Bouguer anomalies may indicate rock types. The Puerto Rico Trench is the deepest part of the Atlantic Ocean, with water depths exceeding 8,400 meters. 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. 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. [11], The remaining gravity anomaly at this point in the reduction is called the free-air anomaly. The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative 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. Because of its high population density and extensive development near the coast, Puerto Rico has a significant risk for earthquakes and tsunamis. [20] Negative isostatic anomalies in Switzerland correlate with areas of active uplift, while positive anomalies are associated with subsidence. Search ADS The large negative gravity anomaly is attributed to a . The Bouguer anomaly includes only the negative correction for the high terrain and so is strongly negative. However, he found that the clock ran too slowly in Cayenne, compared with the apparent motion of the stars. We document the spatial and temporal variability of. Journal of Geophysical Research B: Solid Earth. A .gov website belongs to an official government organization in the You could not be signed in. 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. 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. 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 free-air anomaly is around +70 mgal along the Andes coast, and this is attributed to the subducting dense slab. The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative Geophysical monograph 14, Am. The gravitational attraction of this layer or plate is taken into account by the Bouguer plate correction, which is 0.0419103 h mgal m2 kg1. Astrophysical Observatory. Figure produced in Google Earth Pro. At a minimum, these include the tidal correction gtid, the terrain correction gT, and the free air correction gFA. [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. 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 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. The unusually deep sea floor is not limited to the trench, but also extends farther south toward Puerto Rico. [3], Gravity anomalies were first discovered in 1672, when the French astronomer Jean Richter established an observatory on the island of Cayenne. 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. 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). The terrain correction is calculated from knowledge of the local topography and estimates of the density of the rock making up the high ground. Carl Bowin, 1972. 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 general survey operating area will be in the Caribbean Ocean, south Puerto Rico and St. Croix islands, in the area of Turner Hole Canyon, Saba Valley, and south of the St. Croix Ridge. The difference between the corrected measured gravity and the normal gravity is the gravity anomaly.[6]. 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. 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). 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. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. [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 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. That is, the Bouguer anomaly is:[12], The Bouguer anomaly is positive over ocean basins and negative over high continental areas. Secure .gov websites use HTTPS Download image (jpg, 44 KB). ROV dives will mostly be conducted during the day, while CTD casts, and multibeam, singlebeam, and sub-bottom acoustic mapping will occur at night when the ROV is on deck. Immediately after the 1946 earthquake, a tsunami struck northeastern Hispaniola and moved inland for several kilometers. . Newly-acquired multibeam bathymetry of the entire Puerto Rico trench reveals numerous retrograde slope failures at various scales at the edge of the carbonate platform north of Puerto Rico and the Virgin Islands. The low-density sediments of the Molasse basin produce a negative anomaly. 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. 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 gravitational body force that acts on a flap of The gravitational attraction of the high terrain is balanced by the reduced gravitational attraction of its underlying low-density roots. Please check your email address / username and password and try again. This platform was horizontally deposited over Cretaceous to Paleocene arc rocks starting in the Late Oligocene. 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. This glider will be recovered several months later by NOAA Ship Nancy Foster when she is operating in the area. Conf., Geol. It is postulated that differential shifts between the Caribbean plate and the underthrust Atlantic plate have occurred at least twice, once in late Eocene to early Oligocene, during which the outer island chain of the northern Lesser Antillean arc was formed, and again sometime since the late Miocene, when the Barbados ridge and associated uplifted topography were formed. The normal gravity accounts for the bulk gravitation of the entire Earth, corrected for its idealized shape and rotation. 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. "Puerto Rico Trench Negative Gravity Anomaly Belt", Studies in Earth and Space Sciences, R. Shagam, R. B. Hargraves, W. J. Morgan, F. B. Crossref. 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. 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. 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. From February 24 through the end of April 2015, three NOAA Ship Okeanos Explorer expeditions legs will involve traveling to areas identified as priority regions for exploration by multiple groups within the U.S. Geological Survey, the NOAA National Marine Fisheries Service, the NOAA National Ocean Service, the Caribbean Fisheries Management Council, Puerto Rico Department of Natural Resources, and other territory and federal partners. 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. Its depth is comparable to the deep trenches in the Pacific Ocean. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. 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. 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. Exclusive Economic Zone surrounding Puerto Rico and the U.S. Virgin Islands, and the Puerto Rico Trench. 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. ) or https:// means youve safely connected to the .gov website. 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. Other corrections are added for various gravitational models. 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). 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. Gravity anomalies are modelled assuming that the crustal thicknesses of the Atlantic and Caribbean Oceans are constant (but different . [16], Forward modelling is the process of computing the detailed shape of the compensation required by a theoretical model and using this to correct the Bouguer anomaly to yield an isostatic anomaly.[17]. The Caribbean plate is roughly rectangular, and it slides eastward at about 2 cm/yr relative to the North American plate. 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. 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. Salt domes are typically expressed in gravity maps as lows, because salt has a low density compared to the rocks the dome intrudes. Studies of free-air gravity anomaly profiles across island arcs show an important belt of positive anomalies seaward of deep-sea trenches. Password and try again because salt has a significant risk for earthquakes tsunamis. At scales between entire mountain ranges and ore bodies, Bouguer anomalies indicate. 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