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The Earth’s Structure from Travel Times Spherically Spherically symmetric symmetric structure: structure: PREM PREM -- Crustal Crustal Structure Structure -- Upper Upper Mantle Mantle structure structure Phase Phase transitions transitions Anisotropy Anisotropy -- Lower Lower Mantle Mantle Structure Structure D” D” -- Structure Structure of of the the Outer Outer and and Inner Inner Core Core 3-D 3-D Structure Structure of of the the Mantle Mantle from from Seismic Seismic Tomography Tomography -- Upper Upper mantle mantle -- Mid Mid mantle mantle -- Lower Lower Mantle Mantle Seismology and the Earth’s Deep Interior The Earth’s Structure Spherically Symmetric Structure Parameters Parameters which which can can be be determined determined for for aa reference reference model model --P-wave P-wavevelocity velocity --S-wave S-wavevelocity velocity --Density Density --Attenuation Attenuation(Q) (Q) --Anisotropic Anisotropicparameters parameters --Bulk Bulkmodulus modulusKKss --rigidity rigidityμμ −−pressure pressure --gravity gravity Seismology and the Earth’s Deep Interior The Earth’s Structure PREM: velocities and density PREM: PREM: Preliminary Preliminary Reference Reference Earth Earth Model Model (Dziewonski (Dziewonski and and Anderson, Anderson, 1981) 1981) Seismology and the Earth’s Deep Interior The Earth’s Structure PREM: Attenuation PREM: PREM: Preliminary Preliminary Reference Reference Earth Earth Model Model (Dziewonski (Dziewonski and and Anderson, Anderson, 1981) 1981) Seismology and the Earth’s Deep Interior The Earth’s Structure Earth’s Regions and Fractional Mass Seismology and the Earth’s Deep Interior The Earth’s Structure The Earth’s Crust: Travel Times Continental Continental crust crust (a) (a) and and oceanic oceanic crust crust (b) (b) with with corresponding corresponding travel-time travel-time curves curves Seismology and the Earth’s Deep Interior The Earth’s Structure The Earth’s Crust: Minerals and Velocities Average Average crustal crustal abundance, abundance, density density and and seismic velocities seismic velocities of of major major crustal crustal minerals. minerals. Seismology and the Earth’s Deep Interior The Earth’s Structure The Earth’s Crust: Crustal Types SS shields, shields, CC Caledonian Caledonian provinces, provinces, VV Variscan Variscan provinces, provinces, RR rifts, rifts, OO orogens orogens Seismology and the Earth’s Deep Interior The Earth’s Structure The Earth’s Crust: Refraction Studies Refraction Refraction profiles profiles across North across North America, America, (reduction velocity (reduction velocity 6km/s) 6km/s) all all the the determination determination of of lateral lateral velocity velocity variations: variations: PmP PmP Moho Moho reflection reflection Pn Pn Moho Moho refraction refraction Pg Pg direct direct crustal crustal wave wave Seismology and the Earth’s Deep Interior The Earth’s Structure The Earth’s crust: Crustal Types Reflection Reflection data data often often show a highly reflective show a highly reflective lower lower crust.This crust.This may may indicate indicate fine fine layering layering or or lamination, lamination, some some transition transition from from crust crust to to upper mantle. upper mantle. TWT TWT two-way two-way traveltimes traveltimes Seismology and the Earth’s Deep Interior The Earth’s Structure The Earth’s crust: Crustal Types Recently Recently compiled compiled world-wide world-wide crustal crustal thickness thickness (km) (km) indicates indicates cratonic cratonic areas areas and and mountain mountain ranges ranges with with active active tectonics. tectonics. These These data data are are important important to to correct correct travel travel times times regionally, regionally, i.e. i.e. calculate calculate the the contribution contribution of of crustal crustal thickness thickness to to aa teleseismic teleseismic travel-time travel-time perturbation. perturbation. Seismology and the Earth’s Deep Interior The Earth’s Structure The Earth’s crust: Crustal Types Left: Left: Crust Crust P-velocity P-velocity profiles profiles for for young young (<20 (<20 million million year) year) oceanic oceanic basin basin structures. structures. Right: Right: Crustal Crustal PP and and SS velocities velocities for for oceanic oceanic regions regions older older than than 20 20 million million years. years. Seismology and the Earth’s Deep Interior The Earth’s Structure The Earth’s Upper Mantle: Athenosphere The The high-velocity high-velocity lid lid above the low velocity above the low velocity zone zone (asthenosphere) (asthenosphere) isis called called the the lithosphere. lithosphere. The The upper-mantle upper-mantle velocity velocity structure structure leads leads to to complex complex ray ray paths. paths. Seismology and the Earth’s Deep Interior The Earth’s Structure Upper Mantle: Phase transitions Upper Upper mantle mantle discontinuities discontinuities (e.g. (e.g. 410km) are caused 410km) are caused by by phase transitions (left: phase transitions (left: low low pressure pressure olivine, olivine, right: right: high high pressure pressure ββspinel) spinel) Various Various upper upper mantle mantle seismic models seismic models and and experimental experimental results results for for minerals minerals and and mineral mineral assemblages. assemblages. Seismology and the Earth’s Deep Interior The Earth’s Structure Upper Mantle: Discontinuities Various Various reflections reflections from upper from upper mantle mantle discontinuities discontinuities are are being being used used to to investigate investigate the the structural structural details details of of the transition zones the transition zones (e.g. (e.g. vertical vertical gradients, gradients, thickness thickness of of transition transition zone, zone, topography topography of of discontinuities, discontinuities, etc.) etc.) Seismology and the Earth’s Deep Interior The Earth’s Structure Upper Mantle: Phase transitions The The location location of of seismic seismic source source within within high high velocity velocity anomalies anomalies indicates indicates downgoing downgoing slab structures. slab structures. Where Where do earthquakes seem do earthquakes seem to to happen happen preferentially? preferentially? Seismology and the Earth’s Deep Interior The Earth’s Structure Upper Mantle: Anisotropy Shear Shear wave wave splitting splitting of of the the SKS SKS phase phase indicates indicates seismic seismic anisotropy anisotropy inin the the upper upper mantle. The alignment mantle. The alignment of of the the anisotropic anisotropic symmetry symmetry system system isis thought thought to to be be correlated with correlated with tectonic tectonic plate plate motion. motion. Seismology and the Earth’s Deep Interior The Earth’s Structure Lower Mantle: D” The The mid-mantle mid-mantle shows shows little little lateral lateral heterogeneity. heterogeneity. The The lowermost lowermost mantle mantle (D”) (D”) hast strong (possibly >10%) lateral velocity perturbations. The may originate hast strong (possibly >10%) lateral velocity perturbations. The may originate inin aa thermal thermal boundary boundary layer layer or or from from subducted subducted lithosphere. lithosphere. Seismology and the Earth’s Deep Interior The Earth’s Structure Lower Mantle: Diffracted Waves The The lowermost lowermost mantle mantle structure structure can can be be studies studies using using waves waves diffracted diffracted at at the the core-mantle core-mantle boundary. boundary. Seismology and the Earth’s Deep Interior The Earth’s Structure The Earth’s Core The The Earth’s Earth’s inner inner core shows core shows considerable considerable anisotropy. anisotropy. TimeTimedependent dependent differential differential travel travel times have led times have led to to the the speculation speculation that that the the Earth’s Earth’s inner inner core core isis rotating rotating faster faster than the than the mantle. mantle. Seismology and the Earth’s Deep Interior The Earth’s Structure The Earth’s Core: Multiples Multiple Multiple reflection reflection ray paths ray paths PK PKnnPP inin the the outer outer core core and recording and recording of of PK PK44PP from from an an underground underground nuclear nuclear explosion. explosion. Seismology and the Earth’s Deep Interior The Earth’s Structure Upper mantle: 3-D structure Seismology and the Earth’s Deep Interior The Earth’s Structure Mid-mantle: 3-D structure Seismology and the Earth’s Deep Interior The Earth’s Structure Lower Mantle: 3-D structure Seismology and the Earth’s Deep Interior The Earth’s Structure Global Cut: 3-D structure Seismology and the Earth’s Deep Interior The Earth’s Structure Geodynamic Modelling: Subduction Zones Perturbation Perturbation of of seismic seismic velocity velocity and and density density for for aa subducting subducting plate plate obtained from numerical convection modelling including phase obtained from numerical convection modelling including phase transitions. transitions. Seismology and the Earth’s Deep Interior The Earth’s Structure Geodynamic Modelling: Subduction Zones Snapshots Snapshots through through subducting subducting slab slab model model and and the the wavefield wavefield perturbation due to the slab. The background model perturbation due to the slab. The background model isis PREM. PREM. Seismology and the Earth’s Deep Interior The Earth’s Structure Geodynamic Modelling: Plumes High-resolution High-resolution numerical numerical study study of of plumes plumes and and the the effects effects of of the the mantle viscosity structure. mantle viscosity structure. Seismology and the Earth’s Deep Interior The Earth’s Structure The Earth’s Structure: Summary The The Earth’s Earth’s seismic seismic velocity velocity structure structure can can be be determined determined from from inverting seismic travel times (e.g. using the Wiechertinverting seismic travel times (e.g. using the WiechertHerglotz Herglotz technique technique for for spherically spherically symmetric symmetric media). media). The The Earth’s Earth’s radial radial structure structure is is dominated dominated by by the the core-mantle core-mantle boundary, boundary, the the inner-core inner-core boundary, boundary, the the upper-mantle upper-mantle discontinuities (410km and 670km) and the discontinuities (410km and 670km) and the crust-mantle crust-mantle transition transition (Moho). (Moho). The The 3-D 3-D structure structure of of the the Earth’s Earth’s interior interior can can be be determined determined by by inverting inverting the the travel-time travel-time perturbations perturbations with with respect respect to to aa spherically spherically symmetric symmetric velocity velocity model model (e.g. (e.g. PREM). PREM). The The positive positive and and negative negative velocity velocity perturbations perturbations are are thought thought to to represent represent cold cold (dense) (dense) or or hot hot (buoyant) (buoyant) regions, regions, respectively. respectively. There There is is remarkable remarkable correlation correlation between between fast fast regions regions and and subductin subductin zones zones as as well well as as slow slow regions regions with with hot-spot hot-spot (plume) (plume) activity. activity. Seismology and the Earth’s Deep Interior The Earth’s Structure