Understanding EarthFifth Edition

Chapter 14:EXPLORING EARTH’S INTERIOR

Copyright © 2007 by W. H. Freeman and Company

Grotzinger • Jordan • Press • Siever

Compressional waveCompressional waveConductionConductionConvectionConvectionCore-mantle boundaryCore-mantle boundaryDepositional remanent magnetismDepositional remanent magnetism

DipoleDipoleGeothermGeothermLower mantleLower mantleLow-velocity zoneLow-velocity zoneMohorovičić discontinuity (Mohorovičić discontinuity (MOHOMOHO))PaleomagnetismPaleomagnetismPhase changePhase changePrinciple of Principle of isostasyisostasySeismic tomographySeismic tomographyShadow zoneShadow zoneShear waveShear waveThermo-remanent magnetizationThermo-remanent magnetization

Concepts we will use in this classConcepts we will use in this classIn bold are the ones I consider most In bold are the ones I consider most

importantimportant

Lecture OutlineLecture Outline

1. Exploring the interior with seismic waves1. Exploring the interior with seismic waves

2. Layering and composition of the interior2. Layering and composition of the interior

3. Earth’s internal heat and temperature3. Earth’s internal heat and temperature

4. 3-Dimensional structure of the mantle4. 3-Dimensional structure of the mantle

5. Earth’s magnetic field5. Earth’s magnetic field

Chapter 14Chapter 14

Exploring Exploring Earth’s Earth’s InteriorInterior

Background facts about Earth’s InteriorBackground facts about Earth’s Interior

• The center of the Earth is about 6400 km The center of the Earth is about 6400 km

below us … the deepest well is 10 km.below us … the deepest well is 10 km.

• Heat inside the Earth drives the core’s Heat inside the Earth drives the core’s

geodynamo and the mantle’s convection. geodynamo and the mantle’s convection.

• Earth’s interior is explored by using Earth’s interior is explored by using

information from seismic waves and their information from seismic waves and their

passage through the body of the Earth.passage through the body of the Earth.

1. Exploring the interior with seismic 1. Exploring the interior with seismic waveswaves

● ● Basic types of wavesBasic types of waves

● ● compressional (P compressional (P waves)waves)

● ● shear (S waves)shear (S waves)

●● Reflection and refractionReflection and refraction

1. Exploring the interior with seismic 1. Exploring the interior with seismic waveswaves

● ● Paths of seismic wavesPaths of seismic waves

● ● wave bending (refraction)wave bending (refraction)

● ● shadow zones (P and S)shadow zones (P and S)

●● reflection at internal reflection at internal boundariesboundaries

P-waveP-wavepathspaths

S-waveS-wavepathspaths

P- andP- andS-waveS-wavepathspathsfrom anfrom anearthquakeearthquake

P-, S-, and surface waveP-, S-, and surface wavepaths: from focus to seismographpaths: from focus to seismograph

P-, S-, and surface wavesP-, S-, and surface wavesrecorded on a seismographrecorded on a seismograph

2. Layering and composition of the 2. Layering and composition of the interiorinterior

(a.k.a. (a.k.a. Seismology model of Seismology model of Earth’s layersEarth’s layers))●● crust and lithospherecrust and lithosphere

●● asthenosphere asthenosphere

●● mantle with internal phasemantle with internal phase change at 400 kmchange at 400 km

2. Layering and composition of the 2. Layering and composition of the interiorinterior

● ● Seismology model of Earth’s Seismology model of Earth’s layerslayers (continued)(continued)

● ● core-mantle boundarycore-mantle boundary

● ● core (inner and outer core)core (inner and outer core)

Earth’sEarth’slayeringlayeringrevealed byrevealed byseismologyseismology

Earth’sEarth’smantlemantlestructurestructurebeneath anbeneath anold oceanold oceanbasin: basin: S-waveS-wavevelocity tovelocity todepth ofdepth of900 km900 km

3. Earth’s internal heat and 3. Earth’s internal heat and temperaturetemperature

● ● Heat flow through Earth’s Heat flow through Earth’s interiorinterior

● ● conduction (lithosphere)conduction (lithosphere)

● ● convection (mantle and convection (mantle and core)core)

TopographyTopographyof mid-oceanof mid-oceanridges in theridges in theAtlantic andAtlantic andPacific oceansPacific oceans

3. Earth’s internal heat and 3. Earth’s internal heat and temperaturetemperature

● ● Temperatures in the EarthTemperatures in the Earth

● ● geothermal gradientgeothermal gradient

● ● normally 20 to 30º C / kmnormally 20 to 30º C / km● ● 1300-14001300-1400ºº C at base of C at base of lithospherelithosphere● ● 3000-60003000-6000ºº C + in core C + in core

An estimateAn estimateof the geotherm:of the geotherm:

temperaturetemperatureincreases with increases with depth in thedepth in theEarthEarth

4. 3-Dimensional structure of the 4. 3-Dimensional structure of the mantlemantle

● ● Seismic Seismic tomographytomography

● ● Earth’s gravity Earth’s gravity fieldfield

● ● The geoidThe geoid

Mantle structureMantle structure

Mantle structureMantle structure

Mantle structureMantle structure

The geoid: The geoid: shape of planet Earthshape of planet Earth

5. Earth’s magnetic field and the 5. Earth’s magnetic field and the dynamodynamo

● ● Earth’s dipole fieldEarth’s dipole field

● ● complexity of the complexity of the magnetic magnetic fieldfield

● ● non-dipole field non-dipole field componentcomponent

● ● secular variations in secular variations in the the fieldfield

● ● magnetic reversalsmagnetic reversals

ChangeChangein thein thelocationlocationof the of the NorthNorthmagneticmagneticpole frompole from1600 to1600 to20002000

Earth’s magnetic field and the geodynamoEarth’s magnetic field and the geodynamo

Earth’s magnetic field and the geodynamoEarth’s magnetic field and the geodynamo

Earth’s Earth’s magnetic magnetic field field and the and the geodynamogeodynamo

Earth’s Earth’s magnetic magnetic field field lineslines

Earth’s Earth’s magnetic magnetic field field reversals:reversals:

Step 1Step 1

Earth’s Earth’s magnetic magnetic field field reversals:reversals:

Step 2Step 2

Earth’s Earth’s magnetic magnetic field field reversals:reversals:

Step 3Step 3

Earth’s Earth’s magnetic magnetic field field reversals:reversals:

Step 4Step 4

5. Earth’s magnetic field and the 5. Earth’s magnetic field and the dynamodynamo

● ● PaleomagnetismPaleomagnetism

● ● records of magnetizationrecords of magnetization

● ● thermo-remanent thermo-remanent ● ● depositional remanentdepositional remanent

● ● magnetic stratigraphymagnetic stratigraphy

ThermoremanentThermoremanent

Depositional remanentDepositional remanent

Depositional remanentDepositional remanent

Magnetic stratigraphyMagnetic stratigraphy

5. Earth’s magnetic field and the 5. Earth’s magnetic field and the dynamodynamo

● ● Magnetic field and the biosphereMagnetic field and the biosphere

● ● magnetic orientationmagnetic orientation

● ● magnetic frame of referencemagnetic frame of reference

● ● field offersfield offers protection fromprotection from

the solar windthe solar wind