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04- Das Erdinnere II Thursday, 12 November 2009 Module BP 11 - 04 Examples of seismic waves P PKiKP PcP PP PKP PKIKP inner core FOCUS outer core mantle ScS SKIKS SS R. Bousquet 2009-2010 S SKS P-wave S-wave Seismic wave paths of some important refracted and reflected Pwave and S-wave phases from an earthquake with focus at the Earth’s surface. Thursday, 12 November 2009 Module BP 11 - 04 30 SKIKS SKS PKP Travel-time, t (min) 20 PKIKP PKIKP PKiKP dP e t ac ScS fr dif S 10 PcP P core shadow-zone for direct P-waves R. Bousquet 2009-2010 core shadow-zone for direct S-waves 0 0 Thursday, 12 November 2009 30 60 90 120 Epicentral distance, 6 ($) 150 180 Travel-time versus epicentral distance (t–∆) curves for some important seismic phases (modified from Jeffreys and Bullen, 1940) Module BP 11 - 04 Fault plane solution D C Ground surface Compression Secondary plane Dilatation H Dilatation R. Bousquet 2009-2010 Fault plane Thursday, 12 November 2009 Compression Module BP 11 - 04 Fault plane solution Sensor C 1st peak upwards Dilatation Fault plane Compression Compression Epicenter Dilatation R. Bousquet 2009-2010 Secondary plane Thursday, 12 November 2009 Sensor D 1st peak downwards Module BP 11 - 04 Fault plane solution N (a) focal sphere H P1 ltfau ne pla S1 S2 P2 P2 P1 R. Bousquet 2009-2010 (b) first motions P T (c) focal mechanism Method of determining the focal mechanism of an earthquake. (a) The focal sphere surrounding the earthquake focus, with two rays S1 and S2 that cut the sphere at P1 and P2, respectively. (b) The points P1 and P2 are plotted on a lowerhemisphere stereogram as first-motion pushes (solid points) or tugs (open points). (c) The best-fitting great circles define regions of compression (shaded) and tension (unshaded). The P- and T-axes are located on the bisectors of the angles between the fault-plane and auxiliary plane. Thursday, 12 November 2009 Module BP 11 - 04 Fault plane solution (a) normal fault The different types of fault plane solution m 3' m 1' P T (b) reverse fault m 1' m 3' T P (c) strike–slip fault R. Bousquet 2009-2010 m 1' Thursday, 12 November 2009 T P m 3' Module BP 11 - 04 Example of Fault plane solution: Atlantic ridge 60$W 75$N 40$W 20$W 0$ 75$N May 31 1971 60$N September 20 1969 April 3 1972 60$N Fault-plane solutions for earthquakes along the MidAtlantic Ridge, showing the prevalence of extensional tectonics with normal faulting in the axial zone of the spreading center (based on data from Huang et al., 1986). April 22 1979 40$N 40$N November 16 1965 June 6 1972 June 28 1977 (1) R. Bousquet 2009-2010 20$N January 29 1982 June 3 1962 May 12 1983 June 2 1965 June 28 1979 January 28 1979 0$ Thursday, 12 November 2009 60$W 20$N June 28 1977 (2) 40$W 20$W 0$ 0$ Romanche fault Module BP 11 - 04 Example of Fault plane solution: Romanche fault n of motio plate n Africa ST. PAUL HE AN C ROM N CHA I R. Bousquet 2009-2010 motion of American plate Fault-plane solutions for earthquakes on the St. Paul, Romanche and Chain transform faults in the Central Atlantic ocean (after Engeln et al., 1986). Most focal mechanisms show right lateral (dextral) motions on these faults, corresponding to the relative motion between the African and American plates. Thursday, 12 November 2009 ridge dextral transform fault shallow reverse fault no relative motion oceanic plate inactive fracture zone, negligible seismicity R. Bousquet 2009-2010 oblique normal fault sinistral transform fault continental plate normal fault subduction zone Module BP 11 - 04 Example of Fault plane solution steep reverse fault Fault-plane solutions for hypothetical earthquakes at an ocean ridge and transform fault system. Note that the sense of movement on the fault is not given by the apparent offset of the ridge. The focal mechanisms of earthquakes on the transform fault reflect the relative motion between the plates. Note that in this and similar figures the sector with compressional first motions is shaded. Thursday, 12 November 2009 Module BP 11 - 04 Examples of seismic waves P PKiKP PcP PP PKP PKIKP inner core FOCUS outer core mantle ScS SKIKS SS R. Bousquet 2009-2010 S SKS P-wave S-wave Seismic wave paths of some important refracted and reflected Pwave and S-wave phases from an earthquake with focus at the Earth’s surface. Thursday, 12 November 2009 Module BP 11 - 04 Simple model of the earth Surface outcrop Seismic reflection & refraction Crust Drillholes (up to ~20 km) Mantle Core R. Bousquet 2009-2010 Gravity, magnetics, heat flow dimishing resolution Earthquakes Seismic Waves (penetrate entire Earth) Thursday, 12 November 2009 center of Earth (6375 km) Magma (fro up to ~200 km) Module BP 11 - 04 Seismic velocities model for the Earth Body-wave velocity (km s –1) 0 10 15 crust 35 660 1000 Depth (km) 3000 4000 R. Bousquet 2009-2010 5 410 2000 Thursday, 12 November 2009 0 5000 6000 VS ` upper mantle VP _ lower mantle 2889 outer core 5154 inner core Module BP 11 - 04 Relation Seismic waves - density Birch’s law (1964) 0.6 GPa Vp Vp 1.0 GPa Vp Vs Vs Velocity (km.s-1) Velocity (km.s-1) 0.2 GPa extended Birch’s law Vs R. Bousquet 2009-2010 Density (g.cm-3) V=aρ+b where a & b are parameters characterizing the rocks and V & ρ are respectively the seismic velocity and the density of the rocks Thursday, 12 November 2009 Density (g.cm-3) Ludwig et al., 1970 Module BP 11 - 04 Simple model of the earth Density differentiation due to changes in chemical composition Crust 2-3 t/m3 3-3 t/m3 Silicates Mantle 5.8 t/m3 Core Iron R. Bousquet 2009-2010 10.8 t/m3 Thursday, 12 November 2009 Silicates rich in Fe & Mg Module BP 11 - 04 Density-pressure inside the Earth 15 6000 Radius (km) 4000 2000 6000 0 400 Gravity (m s – 2) 10 300 200 5 mantle 5 0 0 Thursday, 12 November 2009 outer core 2000 4000 Depth (km) outer core inner core inner core 6000 100 0 0 2000 4000 Depth (km) 6000 0 Pressure (GPa) Density (103 kg m– 3 ) 10 mantle R. Bousquet 2009-2010 0 Radius (km) 4000 2000 Hard solid Solid Hard solid Crust 29 R. Bousquet 2009-2010 Lithosphere Thursday, 12 November 2009 Asthenosphere Liquid Solid Inner Core km gT&P 51 00 increasi n 00 km Outer Core upper mantle 10 0-2 0 65 0- 0 70 km m k 0 Module BP 11 - 04 Physical state due to increasing T and P with Depth Lower mantle Module BP 11 - 04 Isothermen in der Erde “Real” geotherm 1000 400 km 13 670 km 24 GP a GP a Mantle 2000 135 3000 outer core 2900 km GP a 4000 5000 329 5100 km GP a inner core 6000 R. Bousquet 2009-2010 1000 2000 3000 Lithosphere Thursday, 12 November 2009 4000 5000 Asthenosphere 6000 Geotherm if the heat tranfer is only due to the conduction Module BP 11 - 04 Model of the Earth CONTINENT LITHOSPHERE rigid 100–150 km thick OCEAN Crust 38–40 km thick Crust 6–8 km thick UPPER MANTLE 0 220 400 670 MESOSPHERE (LOWER MANTLE) semi-solid, plastic Depth (km) 2891 R. Bousquet 2009-2010 OUTER CORE fluid Thursday, 12 November 2009 5150 CORE rigid 6371 LITHOSPHERE rigid 70–100 km thick ASTHENOSPHERE partially molten phase transition olivine –> spinel phase transition spinel –> oxides, perovskite Module BP 11 - 04 Description of the Earth: the crust CONTINENT LITHOSPHERE rigid 100–150 km thick OCEAN Crust 38–40 km thick Crust 6–8 km thick UPPER MANTLE 0 220 400 670 MESOSPHERE (LOWER MANTLE) semi-solid, plastic Depth (km) 2891 OUTER CORE fluid 5150 CORE rigid R. Bousquet 2009-2010 6371 Thursday, 12 November 2009 LITHOSPHERE rigid 70–100 km thick ASTHENOSPHERE partially molten phase transition olivine –> spinel phase transition spinel –> oxides, perovskite Oceanic crust: 0.099% of Earth's mass; depth of 0-10 kilometers The oceanic crust contains 0.147% of the mantle-crust mass. The majority of the Earth's crust was made through volcanic activity. The oceanic ridge system, a 40,000-kilometer network of volcanoes, generates new oceanic crust at the rate of 17 km3 per year, covering the ocean floor with basalt. Hawaii and Iceland are two examples of the accumulation of basalt piles. Continental crust: 0.374% of Earth's mass; depth of 0-50 kilometers. The continental crust contains 0.554% of the mantle-crust mass. This is the outer part of the Earth composed essentially of crystalline rocks. These are low-density buoyant minerals dominated mostly by quartz (SiO2) and feldspars (metal-poor silicates). The crust (both oceanic and continental) is the surface of the Earth; as such, it is the coldest part of our planet. Because cold rocks deform slowly, we refer to this rigid outer shell as the lithosphere (the rocky or strong layer). 0 Depth (km) Module BP 11 - 04 Description of the Earth: the crust 0 5 10 P-wave velocity (km s– 1) 2 4 6 8 Generalized petrological model and P-wave velocity–depth profile for oceanic crust ocean bottom ocean crust ~ 7 km thick Moho 15 0 top of basement Depth (km) oceanic sediments Layer 2 basalt Layer 3 gabbro ultramafics Generalized petrological model and P-wave velocity–depth profile for continental crust near-surface low-velocity layer 10 R. Bousquet 2009-2010 Layer 1 upper mantle P-wave velocity (km s– 1) 4 6 8 sea water Cenozoic sediments Mesozoic & Paleozoic sediments 20 Conrad laminations 30 Thursday, 12 November 2009 Moho zone of positive velocity gradient sialic low-velocity layer middle crustal layer upper crystalline basement granitic laccoliths migmatites high-velocity tooth amphibolites lower crustal layer granulites uppermost mantle ultramafics Module BP 11 - 04 Description of the Earth: the upper mantle CONTINENT LITHOSPHERE rigid 100–150 km thick OCEAN Crust 38–40 km thick Crust 6–8 km thick UPPER MANTLE 0 220 400 670 MESOSPHERE (LOWER MANTLE) semi-solid, plastic Depth (km) 2891 OUTER CORE fluid 5150 CORE rigid R. Bousquet 2009-2010 6371 Thursday, 12 November 2009 LITHOSPHERE rigid 70–100 km thick ASTHENOSPHERE partially molten phase transition olivine –> spinel phase transition spinel –> oxides, perovskite Upper mantle: 10.3% of Earth's mass; depth of 10-400 kilometers The upper mantle contains 15.3% of the mantle-crust mass. Fragments have been excavated for our observation by eroded mountain belts and volcanic eruptions. Olivine (Mg,Fe) 2SiO4 and pyroxene (Mg,Fe)SiO3 have been the primary minerals found in this way. These and other minerals are refractory and crystalline at high temperatures; therefore, most settle out of rising magma, either forming new crustal material or never leaving the mantle. Part of the upper mantle called the asthenosphere might be partially molten. Module BP 11 - 04 Description of the Earth: the upper mantle 0 P-wave velocity (km s–1) 6 7 8 9 10 11 0 crust lid 600 1000 Thursday, 12 November 2009 upper mantle 400 km discontinuity 400 800 R. Bousquet 2009-2010 low-velocity layer 670 km discontinuity lower mantle Depth (km) 200 5 10 Epicentral distance, 6 ($) 15 20 25 30 35 40 Mineral Composition 2 R. Bousquet 2009-2010 Module BP 11 - 04 Description of the Earth: the upper mantle Thursday, 12 November 2009 R. Bousquet 2009-2010 Module BP 11 - 04 Description of the Earth: the upper mantle Phase Transformation Olivine undergoes pressure dependent transformation to the spinel structure (Ringwoodite), and then breaks down to Perovskovite. The transformations correlate with the major seismic discontinuities, and probably generate part of the Signal. Thursday, 12 November 2009 Module BP 11 - 04 Description of the Earth: the upper mantle € € R. Bousquet 2009-2010 € Olivine Phases (Mg,Fe) 2 SiO4 = (Mg,Fe) 2 SiO4 Olivine Wadsleyite Pressure 13-14 GPa 410 km. (Mg,Fe) 2 SiO4 = (Mg,Fe) 2 SiO4 Wadsleyite Ringwoodite Pressure 18 GPa. 520 km. (Mg,Fe) 2 SiO4 = (Mg,Fe)SiO3 + (Mg,Fe)O Ringwoodite Peroskovite Magnesiowüstite Thursday, 12 November 2009 Pressure 23 GPa. 660 km. Module BP 11 - 04 Description of the Earth: the upper mantle Mineralogy of the mantle: influence of the chemical composition 60 Perovskite (Pv) + Magnesiowüstite (Mw) 1400 50 1200 Pressure (GPa) 40 Pv + Mw + St 1000 2 Magnesio- wüstite (Mw) + Stishovite (St) 30 800 a + Pv + Mw 600 20 a + Mw + St `-Phase (`) Spinel (a) ` + a 400 _ + a 10 _ + ` 200 R. Bousquet 2009-2010 Olivine (_) 0 0 0.8 Mg2SiO4 Thursday, 12 November 2009 0.6 0.4 Composition 0.2 1 Fe2SiO4 Module BP 11 - 04 Description of the Earth: transition zone CONTINENT LITHOSPHERE rigid 100–150 km thick OCEAN Crust 38–40 km thick Crust 6–8 km thick UPPER MANTLE 0 220 400 670 MESOSPHERE (LOWER MANTLE) semi-solid, plastic Depth (km) 2891 OUTER CORE fluid 5150 CORE rigid R. Bousquet 2009-2010 6371 Thursday, 12 November 2009 LITHOSPHERE rigid 70–100 km thick ASTHENOSPHERE partially molten phase transition olivine –> spinel phase transition spinel –> oxides, perovskite Transition region: 7.5% of Earth's mass; depth of 400-650 kilometers The transition region or mesosphere (for middle mantle), sometimes called the fertile layer, contains 11.1% of the mantle-crust mass and is the source of basaltic magmas. It also contains calcium, aluminum, and garnet, which is a complex aluminum-bearing silicate mineral. This layer is dense when cold because of the garnet. It is buoyant when hot because these minerals melt easily to form basalt which can then rise through the upper layers as magma. Module BP 11 - 04 Description of the Earth: transition zone Pyroxene - Garnet Phases Transformation of non-olivine components are also important (30%). This phase changes are gradual and lead to changes of slope of velocity. Pyroxene starts to dissolve into the garnet Structure at 350 - 500 km. R. Bousquet 2009-2010 At about 580 km CaSiO3 perovskovite Exsolves from garnet. Thursday, 12 November 2009 Module BP 11 - 04 Description of the Earth: the lower mantle CONTINENT LITHOSPHERE rigid 100–150 km thick OCEAN Crust 38–40 km thick Crust 6–8 km thick UPPER MANTLE 0 220 400 670 MESOSPHERE (LOWER MANTLE) semi-solid, plastic Depth (km) 2891 OUTER CORE fluid 5150 CORE rigid R. Bousquet 2009-2010 6371 Thursday, 12 November 2009 LITHOSPHERE rigid 70–100 km thick ASTHENOSPHERE partially molten phase transition olivine –> spinel phase transition spinel –> oxides, perovskite Lower mantle: 49.2% of Earth's mass; depth of 650-2’890 kilometers The lower mantle contains 72.9% of the mantle-crust mass and is probably composed mainly of silicon, magnesium, and oxygen. It probably also contains some iron, calcium, and aluminum. Scientists make these deductions by assuming the Earth has a similar abundance and proportion of cosmic elements as found in the Sun and primitive meteorites. D": 3% of Earth's mass; depth of 2’700-2’890 kilometers This layer is 200 to 300 kilometers (125 to 188 miles) thick and represents about 4% of the mantlecrust mass. Although it is often identified as part of the lower mantle, seismic discontinuities suggest the D" layer might differ chemically from the lower mantle lying above it. Scientists theorize that the material either dissolved in the core, or was able to sink through the mantle but not into the core because of its density. Module BP 11 - 04 Description of the Earth: the outer core CONTINENT LITHOSPHERE rigid 100–150 km thick OCEAN Crust 38–40 km thick Crust 6–8 km thick UPPER MANTLE 0 220 400 670 MESOSPHERE (LOWER MANTLE) semi-solid, plastic Depth (km) 2891 OUTER CORE fluid 5150 CORE rigid R. Bousquet 2009-2010 6371 Thursday, 12 November 2009 LITHOSPHERE rigid 70–100 km thick ASTHENOSPHERE partially molten phase transition olivine –> spinel phase transition spinel –> oxides, perovskite Outer core: 30.8% of Earth's mass; depth of 2,890-5,150 kilometers The outer core is a hot, electrically conducting liquid within which c o n v e c t i v e mo t i o n o c c u rs . Th i s conductive layer combines with Earth's rotation to create a dynamo effect that maintains a system of electrical currents known as the Earth's magnetic field. It is also responsible for the subtle jerking of Earth's rotation. This layer is not as dense as pure molten iron, which indicates the presence of lighter elements. Scientists suspect that about 10% of the layer is composed of sulfur and/or oxygen because these elements are abundant in the cosmos and dissolve readily in molten iron. Module BP 11 - 04 Description of the Earth: the inner core CONTINENT LITHOSPHERE rigid 100–150 km thick OCEAN Crust 38–40 km thick Crust 6–8 km thick UPPER MANTLE 0 220 400 670 MESOSPHERE (LOWER MANTLE) semi-solid, plastic Depth (km) 2891 OUTER CORE fluid 5150 CORE rigid R. Bousquet 2009-2010 6371 Thursday, 12 November 2009 LITHOSPHERE rigid 70–100 km thick ASTHENOSPHERE partially molten phase transition olivine –> spinel phase transition spinel –> oxides, perovskite Inner core: 1.7% of the Earth's mass; depth of 5,150-6,370 kilometers The inner core is solid and unattached to the mantle, suspended in the molten outer core. It is believed to have solidified as a result of pressurefreezing which occurs to most liquids when temperature decreases or pressure increases. Module BP 11 - 04 Comparison of the different planets The internal structure of the terrestrial planets are similar. They all have Core – High density metal Mantle – Medium density rocky materials, such as silica (SiO2), hot, semi-solid Crust – lowest density rocks, such as granite and basalt (black lava rock…) The layering of different density materials occurs due to differentiation – heavy materials sink to the bottom while lighter material rise to the top… R. Bousquet 2009-2010 Lithosphere: The coolest and most rigid layer of rock near a planet’s surface. Molten lava of Earth exists at a very narrow region beneath the lithosphere Thursday, 12 November 2009 R. Bousquet 2009-2010 Module BP 11 - 04 A nother view of the Earth Thursday, 12 November 2009 Module BP 11 - 04 Origin of the Geoid : density anomalies Geoid over India R. Bousquet 2009-2010 Blue=low gravity Red = high gravity Seismic tomography in the mantle Blue=“cold”=“more dense” Red = “hot” = “less dense” It is very clear that long wavelength Geoid lows are associated to cold and dense material in the mantle. Therefore : Long wavelength Geoid = density anomalies in the mantle short wavelength Geoid = surface topography (i.e. mountains) Thursday, 12 November 2009 Mittelozeanischer Rücken Kontinentale Rift Zone Aktiver Kontinentalrand Ozean. Insel Tiefe km 0 Kruste Spinell Granat phäre os phäre os 100 1000°C 3,5 Li As the th n Module BP 11 - 04 Summary of the structure of the Earth Basalt Su 7,0 SpinellPeridotit n tio uk bd 200 300 Grenat + Pyroxen Majorit Oberer Mantel 400 Olivin Phasen-Übergang Spinell Phase 13 GranatPeridotit 500 Druck GPa 600 Temperatur Spinell Phase Phasen-Übergang R. Bousquet 2009-2010 700 Thursday, 12 November 2009 24 2000°C Perowskit + Magnesiowüstit Unterer Mantel 2900 Post-Perowskit Phasen-Übergang Eisen+ Nickel + geringe Anteile flüssig leichterer Elemente 5080 Kern fest verändert nach STOSCH (2002) 4000°C