Moho mohorovicic discontinuity accessscience from mcgraw. Research gutenberg discontinuity world of scientific discovery. What is the mohorovicic discontinuity and where is it found. Learn vocabulary, terms, and more with flashcards, games, and other study tools. The moho lies almost entirely within the lithosphere. Mohorovicic discontinuity moho and provide information on the velocity structure and physical properties of the crust. In geology the word discontinuity is used for a surface at which seismic waves change velocity. The mohorovicic discontinuity moho defines the boundary between the earths crust and mantle. Multiple choice questions for interior of the earth chapter 17. It is defined by the distinct change in velocity of seismological waves as they pass through changing densities of rock.
Mohorovicic discontinuity definition, the discontinuity between the crust and the mantle of the earth, occurring at depths that average about 22 miles 35 km beneath the continents and about 6 miles 10 km beneath the ocean floor. Mohorovicic discontinuity depth analysis beneath north. The name of the discontinuity is now commonly contracted to the moho. The mohorovicic seismic discontinuity, known today as the moho, was discovered in 1909 by andrija mohorovicic. A low seismic velocity zone is located at about 100350 km within the earth. Unit 1 landforms and water forms earth is divided into specific structural zones. He had seismographs installed before the 1909 earthquake had occurred. The mohorovicic discontinuity the moho is the boundary lying between the crust and the mantle of the earth across which seismic waves change velocities. Isostatic constraints demonstrate that in continent. The origin of a seismic discontinuity associated with this interface, known as the gutenberg discontinuity g, remains enigmatic. Jun 24, 2015 the mohorovicic discontinuity moho is the surface that limits the earths crust and mantle. Project mohole was an attempt to retrieve a sample of material from the earths mantle by drilling a hole through the earths crust to the mohorovicic discontinuity, or moho. What is the mohorovicic discontinuity and where is it.
The mohorovicic discontinuity is a discontinuity in the composition of solid rock, but it is indeed solid on both sides. Lithosphere rigid mantle 150 km depth low velocity zone partially melted, 100150 km depth upper mantle merge into the lines given by equations i and 2 without marked discontinuity. Conrad continental crust gutenberg disconitnuidad mantle lehmann upper mantle. Despite the detection of the l, the existence of a global discontinuity at this depth is still under discussion. Wave velocities below the mohorovicic discontinuity. The nature of the mohorovicic discontinuity, a compromise. The uppermost section of the outer core is thought to be about 1, k hotter than the overlying mantle, creating a thermal boundary layer. The project was suggested in march 1957 by walter munk, nas member 1956 and member of the national science foundation nsf earth science panel. One of these surfaces exists at an average depth of 8 kilometers beneath the ocean basin and at an average. Mohorovicic discontinuity synonyms, mohorovicic discontinuity pronunciation, mohorovicic discontinuity translation, english dictionary definition of mohorovicic discontinuity. The mohorovicic discontinuity tends to be a mirror image of surface topography. Most of the regions where the l has been detected belong to continental or island arc regions. Tolstoy, maya lamont doherty earth observatory, columbia university, palisades, new york. Oceanic crust and mantle structure the surface is the top of the mantle the mohorovicic discontinuity, see page 63, and the bottom is the coremantle boundary cmb.
This happens at the mohorovicic discontinuity, where, the pressure and temperature of rocks are high enough that the rocks become plastic, rather than brittle. The marked decrease in amplitude noted by wilson and baykal can be accounted for by the relatively steep slope of our group velocity curve for periods below 18 sec. It was determined that seismic waves with travel paths that were relatively deep in the earth below about 15km oceans and about 30km continents went zipping along quite quickly. Department of geophysics, colorado school of mines, golden, co 80401, usa article info abstract article history. Mohorovicic discontinuity article about mohorovicic. Its significance stems from its clear demarcation of the first boundary of the chemically differentiated solid earth. Wyllie department of geochemistry and minemlogy pennsylvania state universit. The moho, often designated the m discontinuity in papers from that period as in fig. The mohorovicic discontinuity croatian pronunciation. Wave velocities below the mohorovicic discontinuity 351 1953 give about 78 and 4. In 1914, germanamerican geologist beno gutenberg 18891960, proved the existence of the core. If youre behind a web filter, please make sure that the domains.
Mapping the moho beneath the southern alps continent. Oct 17, 2012 mohorovicic discontinuity below the central indian ocean basin deformation zone as inferred from gravity modelling. Kennett b a geology section, ign, department of geosciences and natural resource management, university of copenhagen, denmark b research school of earth sciences, the australian national university, canberra act 0200, australia 1. The initial depths of conrad and moho discontinuities are 12 and 30 km, respectively. Geography exam final geog 101 with sahno at unlv school of. May 20, 2016 the mohorovicic discontinuity, also known as the moho, is a discrete jump in seismic wave velocities a seismic discontinuity that has come to define the boundary between the crust and the mantle. Aug 01, 2017 the mohorovicic discontinuity the moho is the boundary lying between the crust and the mantle of the earth across which seismic waves change velocities. It began about 150 degrees from the earthquake epicenter, and formed a bulleye on the side of the earth opposite from the earthquake. The mohorovicic discontinuity was discovered in by andrija mohorovicic, a croatian seismologist. Geography exam final geog 101 with sahno at unlv school. Hales discontinuity contents gutenberg discontinuity the gutenberg the g revenaugh and jordan, 1991b or 8 discontinuity thybo and perchuc, 1997 marks the transition from the lid, which is defined as the uppermost mantle beneath the moho, to the lowvelocityzone lvz, which characterizes the transition to the convecting. Modern instruments have determined that the velocity of seismic wave s increases rapidly at this boundary. Introduction 2 the most important compositional and density boundary in the lithosphere is the moho, which is generally regarded as the boundary that separates intermediate.
Conrad discontinuity upper lower crust boundary mohorovicic discontinuity base of continental crust 3550 km continents. Moho mohorovicic discontinuity moho mohorovicic discontinuity article by. The mohorovicic discontinuity or moho is the boundary between the cryst and the mantle. This discontinuity at a depth of 210 km is also called the lehmann discontinuity the l. Evolution of the archean mohorovicic discontinuity from a synaccretionary 4. This area is generally complex because at these temperatures, the atoms are. The available experimental data and steadystate calculations make it difficult to explain the m discontinuity beneath both oceans and continents on the basis of the same. The nature of the transition between crust and mantle is not always sharp and considerable variety in character and depth has been revealed across the globe. Conrad discontinuity article about conrad discontinuity. May 10, 2016 the mohorovicic discontinuity is a discontinuity in the composition of solid rock, but it is indeed solid on both sides.
This is a weak, easily formed, and flowing zone of plastic rock in which seismic waves slow considerably. Mohorovicic discontinuity boundary between mantle lithosphere, at which earthquake waves. This boundary is located approximately 24 miles below the earths surface and 6 miles below the oceanic floor, a distance which varies from place to place. A the heavier, ultramafic mantle, occurs earthquakes in at a depth of about 35 kilometers under ns in modern the continental shield areas and about r in all direc 10 kilometers below sea level in the possible paths ocean basins. It appears beneath continents, but not usually beneath oceans, and does not readily appear in globally averaged studies. It lies on average 3050 km below the surface on cobtinents, but 5. The mohorovicic seismic discontinuity boundary between crust and mantle or moho if youre seeing this message, it means were having trouble loading external resources on our website. The boundary between the earths crust and the underlying mantle, averaging 8 kilometers in depth under the oceans and 32 kilometers in depth under the. Cartoon of the mechanism leading to a velocity change due to a change of anisotropy structure. Velocities of seismic waves were used to identify this boundary. It was discovered by croatian seismologist andrija mohorovicic. Initial values of station corrections are taken to be zero. Mohorovicic discontinuity, often called moho, is the boundary between earths crust and mantle see the image below.
Highfrequency ss precursors sampling below the pacific plate intermittently detect the g as a sharp, negative velocity contrast at 40 to 75kilometer depth. Multiple choice questions for interior of the earth. Basic facts about the nature of the boundary, and changes across it, are described. Jul 10, 2016 the mohorovicic discontinuity or moho is the boundary between the cryst and the mantle. Conrad discontinuity named after the austrian geophysicist v. Evolution of the archean mohorovicic discontinuity from a. Mohorovicic discontinuity below the central indian ocean basin deformation zone as inferred from gravity modelling. While the mantle has liquid further down, its solid at the top just like the crust but with a different mineral composition. It is of paramount importance in understanding and investigating the dynamics of the earths interior. Moho, or mohorovicic discontinuity, boundary between the earths crust and its mantle. Research gutenberg discontinuity world of scientific. Received 22 march 20 received in revised form 18 july 20 accepted 5 august 20 available online xxxx keywords. It is defined by a jump in seismic velocities from 5. In 1909, andrija mohorovicic 18571936 discovered a distinct layer just beneath the crust, the earths mantle.
The mohorovicic discontinuity, or moho, is the boundary between the crust and the mantle. The moho was discovered by old professor mohorovicic in the early 1900s. Mohorovicic discontinuity definition of mohorovicic. The nature of the mohorovicic discontinuity, a compromise 1 peter j. The mohorovic discontinuity is the division between the lithosphere, and asthenosphere. The existence of the mohorovicic discontinuity has been determined from seismic data. The lower boundary of the mantle is with the core, and the upper boundary is with the crust. Above the 210 the material is highly anisotropic v merge into the lines given by equations i and 2 without marked discontinuity. Crustal structure and surfacewave dispersion 275 greater than 20 sec. These new velocitydepth curves for depths greater than 6okm merge into the lines given by equations i and 2 without marked discontinuity.
Department of geology and geophysics, university of wyoming, laramie, wyoming. It is the boundary at which the earth turns from solid to molten, and the velocity of seismic waves is said to increase quickly at this boundary. The mohorovicic discontinuity, or moho, defines a sharp increase in seismic velocities that usually lies 6 to 8 kilometers below the seafloor. The mohorovicic discontinuity, also known as the moho, is a discrete jump in seismic wave velocities a seismic discontinuity that has come to define the boundary between the crust and the mantle. The moho, as it is often called for brevity, is the boundary between the crust and the mantle. The lehmann discontinuity is an abrupt increase of pwave and swave velocities at the depth of 220 km 140 mi, discovered by seismologist inge lehmann. The mohorovicic seismic discontinuity video khan academy. The moho lies at a depth of about 22 mi 35 km below continents and about 4. Because the pnvelocity and moho depth cannot be solved simultaneously, many inversions were carried out with constant pnvelocity being changed gradually from 7. Pronunciation of andrija mohorovicic with 2 audio pronunciations, 2 synonyms, 1 meaning, 2 translations and more for andrija mohorovicic. Geography notes form 1 free download kcse revision. These observations lie near the depth of the lab in. Pronunciation of andrija mohorovicic with 2 audio pronunciations, 2 synonyms, 1 meaning, 2 translations and.
Deals with the study of natural physical environment of human kind. Andrya mohorovicic determined the boundary between the crust and the mantle, which is now named the mohorovicic discontinuity. It is believed it is composed of garnet peridotite with an average density of 5. Hales discontinuity contents gutenberg discontinuity the gutenberg the g revenaugh and jordan, 1991b or 8discontinuity thybo and perchuc, 1997 marks the transition from the lid, which is defined as the uppermost mantle beneath the moho, to the lowvelocityzone lvz, which characterizes the transition to. Introduction in october 1909 an earthquake near pokupsko.
194 1301 1501 649 583 864 805 1296 455 162 215 477 394 182 1160 1387 1430 485 1056 317 1329 259 469 1317 953 628 605 135 302 181 799 450 447 184