Tectonophysics: Dynamics of lithosphere and mantle: general (1213); Tectonophysics: Dynamics: gravity and tectonics; Tectonophysics: Subduction zone processes (1031; Marine Geology and Geophysics: Subduction zone processes (1031; Geodesy and Gravity: Gravity anomalies and Earth structure (0920. 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). Correcting for these effects removed most of this anomaly. 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 Bouguer anomaly over continents is generally negative, especially over mountain ranges. (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. 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. You could not be signed in. The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. The free-air anomaly is around +70 mgal along the Andes coast, and this is attributed to the subducting dense slab. The rate at which these plates come together is similar to the rate at which a human fingernail grows. Summary. Because the island lies on an active plate boundary, earthquakes are a constant threat, and the densely populated coastal areas are vulnerable to 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. subducts, or slides, under another one. 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. These are indications of strong dynamic effects in subduction zones. 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 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. A tilted carbonate platform provides evidence for extreme vertical tectonism in the region. The main topographic features of this area include: the Lesser Antilles volcanic arc, the old inactive volcanic arc of the Greater Antilles (Virgin Islands to Hispaniola), and the Caribbean and North American oceanic plates. The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative [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. Click image for larger view and image credit. A 1918 magnitude 7.5 earthquake resulted in a tsunami that killed at least 40 people in northwestern Puerto Rico. [13], The remaining gravity anomaly at this point in the reduction is called the Bouguer anomaly. In contrast, the Caribbean plate farther east overrides the North American plate, creating the island arc of the Lesser Antilles with its active volcanoes. You do not have access to this content, please speak to your institutional administrator if you feel you should have access. It is concluded that the Mohorovii discontinuity (characterized by compressional-wave velocities of about 8 km/sec) lies at 9 km. Trenches in the Pacific are located in places where one tectonic plate subducts or slides under another one. 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. Local measurements of the gravity of Earth help us to understand the planet's internal structure. Other Puerto Rican cities also have substantial risk. 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). 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. (or is it just me), Smithsonian Privacy 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. Secure .gov websites use HTTPS 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. For example, a local positive anomaly may indicate a body of metallic ores. 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. 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. 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. 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. The data collected by the Okeanos Explorer during this exploration will improve our understanding of the unique geology and biology of the U.S. ) or https:// means youve safely connected to the .gov website. Event l, Active tectonic regions where plate boundaries transition from subduction to strike slip can take several forms, such as triple junctions, acute, and obtuse corners. 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. Figure 1. Results of the seismic investigation of the Puerto Rico trench and outer ridge, carried out in 1959 by Lamont Geological Observatory, Woods Hole Oceanographic Institution, A. and M. College of Texas, New seismic and magnetic information from the Antilles Outer Ridge and Trench region has been combined with previous geophysical observations to provide an explanation for the origin of the crust, A crustal section across the Puerto Rico Trench, from 450 km north to 250 km south of San Juan, was deduced from seismic refraction and gravity data. 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. Semantic Scholar is a free, AI-powered research tool for scientific literature, based at the Allen Institute for AI. Location of earthquakes as a function of depth and size in the northeastern Caribbean. 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. For full access to this pdf, sign in to an existing account, or purchase an annual subscription. This belt of positive anomalies is called the Outer Gravity High. Bathymetry of the northeast corner of the Caribbean plate. Over a few hundreds or thousands of years several meters of motion accumulate resulting inoccasionalearthquakes and associated landslides and tsunamis. Notice, Smithsonian Terms of The low-density sediments of the Molasse basin produce a negative anomaly. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. [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). 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. [3], Gravity anomalies were first discovered in 1672, when the French astronomer Jean Richter established an observatory on the island of Cayenne. 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). This platform was horizontally deposited over Cretaceous to Paleocene arc rocks starting in the Late Oligocene. Probability for damaging ground motion at San Juan and Mayaguez in comparison to other seismic high-risk areas in the U.S. (e.g. Plate convergence is highly oblique (2010), resulting in a complex crustal boundary with along-strike segmentation, strain partitioning and microplate tectonics. Crossref. 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. Atlantic puerto rico trench gravity anomaly Rico Trench is assumed to be caused by a downwards bending of gravity... Rocks starting in the northeastern Caribbean the Bouguer anomaly do not have access tectonic subducts! 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