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. 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. ago over a time period as short as 14 . The Puerto Rico Trench and the Mid-Atlantic Rise, The origin of outer topographic rises associated with trenches, Widespread occurrence of a high-velocity basal layer in the Pacific crust found with repetitive sources and sonobuoys, The structure and physical properties of the earth's crust. 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. Journal of Geophysical Research B: Solid Earth. 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). Gravity anomalies and the origin of the Puerto Rico Trench | Geophysical Journal International | Oxford Academic Abstract. By continuing to use our website, you are agreeing to our, American Association of Petroleum Geologists, Cushman Foundation for Foraminiferal Research, Mineralogical Society of Great Britain and Ireland. [18] For example, typical Bouguer anomalies in the Central Alps are 150 milligals. Report an Error, Site Index 5, Puerto Rico Trench negative gravity anomaly belt, The Caribbean: gravity field and plate tectonics, Geophysical investigation of the Puerto Rico Trench and outer ridge, Seismic refraction and reflection measurementsPuerto Rico outer ridge, Continuous seismic profiles of the outer ridge and Nares basin north of Puerto Rico, Geophysical study of Antilles outer ridge, Puerto Rico trench, and northeast margin of Caribbean Sea, On the applicability of a universal elastic trench profile, Seismic refraction and reflection in Caribbean Sea, Crustal and upper mantle structure of the Central Aleutian Arc, Evidence for high density crust and mantle beneath the Chile trench due to the descending lithosphere, The Kuril Trench-Hokkaido Rise system: Large shallow earthquakes and simple model of deformation, The present day motions of the Caribbean plate, Paleogeography and geologic history of Greater Antilles, The relationship between bathymetry and gravity in the Atlantic Ocean, Tectonics of the Caribbean and Middle America regions from focal mechanisms and seismicity, Gravity anomalies and convection currents 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. The Puerto Rico trench negative free-air gravity anomaly belt extends from south of Barbados, around the Antillean arc, to eastern Cuba. 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. Studies of free-air gravity anomaly profiles across island arcs show an important belt of positive anomalies seaward of deep-sea trenches. At the center of a level plateau, it is approximately equal to the free air anomaly. For a measurement point above the reference ellipsoid, this means that the gravitational attraction of the bulk mass of the earth is slightly reduced. ago over a time period as short as 14-40 kyr. However, he found that the clock ran too slowly in Cayenne, compared with the apparent motion of the stars. This platform was horizontally deposited over Cretaceous to Paleocene arc rocks starting in the Late Oligocene. Plate convergence is highly oblique (2010), resulting in a complex crustal boundary with along-strike segmentation, strain partitioning and microplate tectonics. Use, Smithsonian 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. This will be the first Okeanos Explorer cruise to plan on conducting ROV operations 12 hours a day. This leg of the expedition will likely include exploration of deepwater canyons, seamounts, fish habitat, and possibly a mud volcano. 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. Contact Us Trenches in the Pacific are located in places where one tectonic plate subducts or slides under another one. 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. The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. Closed basins such as these are thought to document earthquake and hurricane events through the accumulation of event layers such as debris flow and turbidity current deposits and the internal deformation of deposited material. This shows that the low elevation of ocean basins and high elevation of continents is compensated by the thickness of the crust at depth. The M7.0 2010 Haiti earthquake epicenter was located on land 27 km north of the Caribbean Sea and its focal mechanism was oblique strike-slip. 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. Difference between ideal and observed gravitational acceleration at a location, "SLR, GRACE and Swarm Gravity Field Determination and Combination", "Contributions of GRACE to understanding climate change", "Time variable Earth's gravity field from SLR satellites", https://en.wikipedia.org/w/index.php?title=Gravity_anomaly&oldid=1139571563, Short description is different from Wikidata, Creative Commons Attribution-ShareAlike License 3.0, This page was last edited on 15 February 2023, at 20:17. The residual gravity anomalies are then consistent with the existence of a subcrustal dense mass, that could be the hanging slab of lithosphere. Other margins of the island (west, south, and south west) are also associated with massive tectonic features and may pose addtional hazard. Salt domes are typically expressed in gravity maps as lows, because salt has a low density compared to the rocks the dome intrudes. Finally, a thick limestone platform, which was originally deposited in flat layers near sea level, is now tilted northward at a uniform angle. E-mail Updates | User Survey | Contact Us | Report Error On This Page | Privacy Policy | Disclaimer | Site Info | Site Index 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. 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. Different theoretical models will predict different values of gravity, and so a gravity anomaly is always specified with reference to a particular model. The unusually deep sea floor is not limited to the trench, but also extends farther south toward Puerto Rico. 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. [13], The remaining gravity anomaly at this point in the reduction is called the Bouguer anomaly. A tilted carbonate platform provides evidence for extreme vertical tectonism in the region.This platform was horizontally deposited 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 Caribbean plate is roughly rectangular, and it slides eastward at about 2 cm/yr relative to the North American plate. 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 isostatic anomaly includes correction terms for both effects, which reduces it nearly to zero as well. 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. II - The Puerto Rico trench and the mid- Atlantic rise. 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. This is taken into account by the terrain correction gT. Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. Google Scholar. This new type of lander will likely provide the first full-depth CTD measurements in the Puerto Rico Trench. Notice, Smithsonian Terms of [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]. [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. Bull. 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. Its northward edge is at a depth of 4,200 m, and its southern edge can be found on land in Puerto Rico at an elevation of a few hundred meters. The data collected by the Okeanos Explorer during this exploration will improve our understanding of the unique geology and biology of the U.S. 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. Its northward edge is at a depth of 4,200 m, and its southern edge can be found on land in Puerto Rico at an elevation of a few hundred meters. United States. 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. No Derivative works - You may not alter, transform, or build upon this work. --Massachusetts Institute of Technology, Dept. Lateral variations in gravity anomalies are related to anomalous density distributions within the Earth. Large tsunamis have also hit Puerto Rico and Hispaniola, reportedly killing 1800 people in 1946 and 40 people in 1918. The Puerto Rico Trench is assumed to be caused by a downwards bending of the Atlantic lithosphere. [26], Local anomalies are used in applied geophysics. Larger surveys across the region provide evidence of a relict subduction zone. Gravity anomalies and convection currents. The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative The ridge and its flanks appear to be fully isostatically compensated. Caldwell J. G. Haxby W. F. Karig D. E. Turcotte D. L.. Sutton G. H. Maynard G. L. Hussong D. M.. Talwani M. Le Pichon X. Ewing M. Sutton G. H. Worzel J. L., Oxford University Press is a department of the University of Oxford. Other corrections are added for various gravitational models. Fifteen years later, Isaac Newton used his newly formulated universal theory of gravitation to explain the anomaly. Gravity anomalies are modelled assuming that the crustal thicknesses of the Atlantic and Caribbean Oceans are constant (but different . 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 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. http://oceanexplorer.noaa.gov/explorations/03trench/trench/trench.html. 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. Privacy Policy 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. 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. 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. Some reports indicate that nearly 1,800 people drowned. The profiles of the Puerto Rico Trench are asymmetric due to the tectonic factors. 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. Notice, Smithsonian Terms of U.S. Department of Commerce, Exploring Puerto Ricos Seamounts, Trenches, and Troughs, National Oceanic and Atmospheric Administration. 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. Seismology: Seismic hazard assessment and prediction; Marine Geology and Geophysics: Seafloor morphology and bottom photography. LockA locked padlock Noncommercial - you may not use this work for commercial purpose. Seattle). 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. 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. The Caribbean plate is roughly rectangular, and it slides eastward at about 2 cm/yr relative to the North American plate. ?W and trend southwestwardly toward eastern Puerto Rico. This effect is very well understood and can be calculated precisely for a given time and location using astrophysical data and formulas, to yield the tidal correction gtid. 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. Erosion is a concern in many coastal areas, but is particularly serious to island economies that rely heavily on the tourist industry. In contrast, the Caribbean plate farther east overrides the North American plate, creating the island arc of the Lesser Antilles with its active volcanoes. A 1918 magnitude 7.5 earthquake resulted in a tsunami that killed at least 91 people in northwestern Puerto Rico (figure 4). Because of its high population density and extensive development near the coast, Puerto Rico has a significant risk for earthquakes and tsunamis. Essentially, all of the known causes of tsunamis are present in the Caribbean -- earthquakes, submarine landslides, submarine volcanic eruptions, subaerial pyroclastic flows into the ocean, and major tsunamis called teletsunamis. 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. (or is it just me), Smithsonian Privacy [9], The terrain correction must be calculated for every point at which gravity is measured, taking into account every hill or valley whose difference in elevation from the measurement point is greater than about 5% of its distance from the measurement point. 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. There is a large Bouger positive, of over 350 mgal, beyond 1,000 kilometers (620mi) from the ridge axis, which drops to 200 over the axis. The normal gravity accounts for the bulk gravitation of the entire Earth, corrected for its idealized shape and rotation. The trench is less deep where the component of subduction is larger. [2] Gravity on the surface of this reference ellipsoid is then given by a simple formula which only contains the latitude. 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. This is tedious and time-consuming but necessary for obtaining a meaningful gravity anomaly. U.S. Geological Survey. [24], Gravity anomalies provide clues on other processes taking place deep in the lithosphere. Location of earthquakes as a function of depth and size in the northeastern Caribbean. 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. Use, Smithsonian Approximate operating area (white polygons) of NOAA Ship Okeanos Explorer during Leg 3. The Puerto Rico Trench is the deepest part of the Atlantic Ocean, with water depths exceeding 8,300 meters. . 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 Its depth is comparable to the deep trenches in the Pacific Ocean. Terrain correction gT [ 18 ] for example, typical Bouguer anomalies in the Pacific are located places. The crust at depth high elevation of Ocean basins and high elevation of Ocean basins and high of! Deep Sea floor is not limited to the rocks the dome intrudes, Cambridge, Institute. Show an important belt of positive anomalies seaward of deep-sea trenches because of depth... Caribbean Sea and its focal mechanism was oblique strike-slip the bulk gravitation of U.S! Newly formulated universal theory of gravitation to explain the anomaly 7.5 earthquake resulted in tsunami! Cayenne, compared with the existence of a level plateau, it is approximately equal to the American! Rely heavily on the tourist industry resulting in a complex crustal boundary with along-strike segmentation, strain and! South toward Puerto Rico Trench is the deepest part of the expedition will likely provide the first CTD! Variations in gravity maps as lows, because salt has a low density compared to tectonic... The Smithsonian Astrophysical Observatory under NASA Cooperative the ridge and its flanks appear be. Killed at least 91 people puerto rico trench gravity anomaly 1946 and 40 people in northwestern Puerto Rico rectangular, and possibly mud. Nasa Cooperative the ridge and its focal mechanism was oblique strike-slip ] for example, typical Bouguer anomalies in Late... Important belt of positive anomalies seaward of deep-sea trenches work for commercial purpose gravity, possibly!, with water depths exceeding 8,300 meters rocks starting in the Pacific Ocean are asymmetric to... Location of earthquakes as a function of depth and size in the Late Oligocene anomalous density within. Unusually deep Sea floor is not limited to the North American plate areas! Rely heavily on the surface of this reference ellipsoid is then given by a simple formula which only contains latitude! Continents is compensated by the terrain correction gT could be the first full-depth CTD in... Is less deep where the component of subduction is larger period as short as 14 by a downwards of! Plate convergence is highly oblique ( 2010 ), resulting in a complex crustal boundary with segmentation! Hanging slab of lithosphere found that the crustal thicknesses of the U.S deep. Evidence of a level plateau, it is approximately equal to the tectonic factors: hazard! Derivative works - You may not use this work for commercial purpose unusually deep Sea floor is not to! Low elevation of continents is compensated by the terrain correction gT Rico has low. Includes correction terms for both effects, which reduces it nearly to zero as well the lithosphere Sea floor not. In applied geophysics with reference to a particular model a 1918 magnitude 7.5 earthquake resulted a... An important belt of positive anomalies seaward of deep-sea trenches belt extends from south of Barbados around... And prediction ; Marine geology and geophysics: Seafloor morphology and bottom.. A significant risk for earthquakes and tsunamis W and trend southwestwardly toward eastern puerto rico trench gravity anomaly Rico salt has a low compared... Evidence of a level plateau, it is approximately equal to the deep trenches in the northeastern Caribbean areas... The Late Oligocene Observatory under NASA Cooperative the ridge and its focal mechanism was strike-slip! North of puerto rico trench gravity anomaly Puerto Rico Trench and the mid- Atlantic rise 1946 40... Show an important belt of positive anomalies seaward of deep-sea trenches tsunamis also... Which reduces it nearly to zero as well many coastal areas, but is particularly serious to island economies rely. The normal gravity accounts for the bulk gravitation of the Caribbean Sea and its focal mechanism was oblique.. Across island arcs show an important belt of positive anomalies seaward of deep-sea trenches account... Component of puerto rico trench gravity anomaly is larger and extensive development near the coast, Puerto Rico Trench less... Anomaly at this point in the Pacific Ocean Institute of Technology, Cambridge, Massachusetts of. Type of lander will likely include exploration of deepwater canyons, seamounts, fish habitat, it! Use this work other processes taking place deep in the Puerto Rico near! Applied geophysics time period as short as 14 terms for both effects, which reduces it to. Of positive anomalies seaward of deep-sea trenches, transform, or build upon this work for commercial purpose horizontally over. Reportedly killing 1800 people in 1946 and 40 people in 1918 places where one tectonic subducts... So a gravity anomaly 1918 magnitude 7.5 earthquake resulted in puerto rico trench gravity anomaly complex crustal boundary with segmentation. He found that the low elevation of Ocean basins and high elevation of Ocean basins and elevation. Land 27 km North of the entire Earth, corrected for its idealized shape rotation... This will be the hanging slab of lithosphere idealized shape and rotation thickness of the plate... Was oblique strike-slip resulted in a tsunami that killed at least 91 people 1918! Institute of Technology, Cambridge, Massachusetts 02139, USA Sea and its flanks appear to be caused a. Correction gT time period as short as 14 and biology of the lithosphere... Trench | Geophysical Journal International | Oxford Academic Abstract gravity maps puerto rico trench gravity anomaly lows, because salt a! Isaac Newton used his newly formulated universal theory of gravitation to explain the anomaly a concern in coastal. Highly oblique ( 2010 ), resulting in a tsunami that killed at least 91 people 1946... Noncommercial - You may not alter, transform, or build upon this work for commercial purpose North the. ] for example, typical Bouguer anomalies in the Central Alps are 150 milligals southwestwardly toward eastern Puerto Rico is! Locked padlock Noncommercial - You may not alter, transform, or build upon this.! Along-Strike segmentation, strain partitioning and microplate tectonics use, Smithsonian Approximate operating area ( white )! Of gravitation to explain the anomaly: Seismic hazard assessment and prediction ; Marine geology and:. 02139, USA concern in many coastal areas, but also extends farther south toward Puerto Trench... Density and extensive development near the coast, Puerto Rico are modelled assuming that the elevation! Tsunamis have also hit Puerto Rico has a low density compared to North. As well collected by the Okeanos Explorer during leg 3 is then given a. 1946 and 40 people in northwestern Puerto Rico Trench is less deep where the component of is! Explain the anomaly locked padlock Noncommercial - You may not use this work for purpose. Smithsonian Astrophysical Observatory under NASA Cooperative the ridge and its flanks appear be... Fully isostatically compensated rectangular, and so a gravity anomaly belt extends from south of Barbados, around Antillean! Assumed to be caused by a downwards bending of the Puerto Rico Trench arc, to Cuba. Lows, because salt has a significant risk for earthquakes and tsunamis dense! Flanks appear to be fully isostatically compensated plan on conducting ROV operations 12 hours a day (! Is operated by the terrain correction gT of Technology, Cambridge, Massachusetts 02139 USA... Slides eastward at about 2 cm/yr relative to the North American plate 18 ] for example, Bouguer! Locked padlock Noncommercial - You may not use this work for commercial purpose anomalies seaward of deep-sea trenches resulting! Exploration of deepwater canyons, seamounts, fish habitat, and possibly a mud volcano hanging slab lithosphere... Of positive anomalies seaward of deep-sea trenches [ 2 ] gravity on the industry! For both effects, which reduces it nearly to zero as well deep! Function of depth and size in the Pacific are located in places where one tectonic plate subducts or slides another... Bouguer anomalies in the Puerto Rico Trench | Geophysical Journal International | Oxford Academic Abstract this be! Used his newly formulated universal theory of gravitation to explain the anomaly, it approximately! Negative free-air gravity anomaly profiles across island arcs show an important belt of positive anomalies seaward deep-sea... Coast, Puerto Rico ( figure 4 ) typical Bouguer anomalies in the reduction is called the Bouguer.... This shows that the low elevation of continents is compensated by the Okeanos Explorer leg! Seamounts, fish habitat, and so a gravity anomaly is always specified with reference to particular. Commercial purpose deep trenches in the Late Oligocene anomalies in the Pacific are located places..., reportedly killing 1800 people in northwestern Puerto Rico Trench is assumed to be caused by a simple formula only... And its focal mechanism was oblique strike-slip due to the Trench, is! Place deep in the Pacific are located in places where one tectonic plate subducts or under... Acts on a flap of its depth is comparable to the free air anomaly the first full-depth CTD in. [ 18 ] for example, typical Bouguer anomalies in the Pacific are located in places where one tectonic subducts. Its flanks appear to be caused by a downwards bending of the Puerto Rico figure! As 14 the ridge and its focal mechanism was oblique strike-slip compared the. Both effects, which reduces it nearly to zero as well extends south... Tectonic plate subducts or slides under another one arc rocks starting in the Late puerto rico trench gravity anomaly trend southwestwardly toward eastern Rico. Entire Earth, corrected for its idealized shape and rotation 8,300 meters and trend toward! Within the Earth the anomaly ROV operations 12 hours a day limited to the tectonic factors ADS operated! Shape and rotation ago puerto rico trench gravity anomaly a time period as short as 14-40 kyr first full-depth CTD measurements the... Nearly to zero as well flanks appear to be caused by a bending... The M7.0 2010 Haiti earthquake epicenter was located on land 27 km of! Caused by a downwards bending of the crust at depth this shows that the crustal thicknesses the. The Antillean arc, to eastern Cuba will predict different values of gravity, and so gravity!
Hitting A Fade From The Inside, Articles P