The Earth’s IThe Earth’s Internal nternal PPropertiesroperties

I. Seismic WavesI. Seismic Waves

A. = Earthquake-generated waves A. = Earthquake-generated waves traveling through thetraveling through the Earth’s interiorEarth’s interior

B. Give us clues to the composition B. Give us clues to the composition of the Earthof the Earth

C. Types of Seismic WavesC. Types of Seismic Waves

1. Surface waves –

travel on the Earth’s surface

2. Body waves –

travel through the Earth’s interior

Body waves

a.a. P-wavesP-waves (primary waves) (primary waves) Compress and expand rockCompress and expand rock Are the fastest of all seismic Are the fastest of all seismic

waveswaves First waves to register on First waves to register on

seismographseismograph

Body wavesb.b. S-waves S-waves (secondary waves) (secondary waves)

Vibrate up and down Vibrate up and down Second waves to register on Second waves to register on a seismographa seismograph

SeismographSeismograph= = Device which measures Device which measures

seismic wavesseismic waves

II. Earth’s internal layersII. Earth’s internal layers Geologists did research with Geologists did research with

seismic waves seismic waves Concluded that the Earth’s Concluded that the Earth’s

interior is interior is layeredlayered..

Earth’s internal layersEarth’s internal layers

Earth’s internal layersEarth’s internal layersA. A. The The CoreCore-- 1. Composed 1. Composed

mostly of iron mostly of iron and nickeland nickel

2. 2. Inner CoreInner Core very very hothot solidsolid Fe & Ni Fe & Ni

due to due to high high pressurepressure of of the Earththe Earth

The The CoreCore (continued) (continued) 3.3.Outer Core Outer Core

less pressureless pressure from the earth from the earth

liquidliquid Fe & Ni Fe & NiFlow in the Flow in the outer core outer core generates an generates an electric current electric current that powers that powers the Earth’s the Earth’s magnetic field.magnetic field.

B. The B. The MantleMantle

Rocky layerRocky layer About 3000km thickAbout 3000km thick

1. Two parts of mantle1. Two parts of mantle

a. a. Lower mantleLower mantle

b. b. Upper mantle Upper mantle –– two sectionstwo sections

b. b. Upper mantleUpper mantlei.i. Asthenosphere - behaves in a Asthenosphere - behaves in a

semi-fluid semi-fluid mannermanner

b. b. Upper mantleUpper mantleii. ii. LithosphereLithosphere- rigid and brittle- rigid and brittle

C. The C. The CrustCrust

1.1. Uppermost portion of the Uppermost portion of the lithospherelithosphere

2.2. Two types of crustTwo types of crust a. a. Oceanic crustOceanic crust - about 10 km - about 10 km

thickthick

C. The C. The CrustCrust b. b. Continental crustContinental crust – –

about 20-60 km thickabout 20-60 km thick

III. Theory of Continental III. Theory of Continental DriftDrift

A. A. Belief that the earth is a Belief that the earth is a dynamic planet with the dynamic planet with the continents in constant motion continents in constant motion (i.e. continents are moving)(i.e. continents are moving)

III. Theory of Continental III. Theory of Continental DriftDrift

B. All continents B. All continents once joined once joined together into together into supercontinentsupercontinent called called Pangea Pangea

(meaning = all (meaning = all land)land)

C. Theory formulated C. Theory formulated by Alfred by Alfred Wegener Wegener

III. Theory of Continental III. Theory of Continental DriftDrift

D. Evidence that supports theory = D. Evidence that supports theory = 1. Geologic (rock)1. Geologic (rock) 2. Biologic (life)2. Biologic (life)

3. Climatological 3. Climatological (past weather)(past weather)4. Continental Shelves fit together 4. Continental Shelves fit together veryvery wellwell

Tectonic PlatesTectonic Plates= moving sections of the lithosphere = moving sections of the lithosphere on which continents lieon which continents lie

IV.IV. Faults FaultsA.A. faultfault = a fracture along which = a fracture along which

visible displacement can be visible displacement can be detected on one side relative detected on one side relative to the other.to the other.

B.B. Types of faultsTypes of faults 1. 1. FootwallFootwall--Fig 23.17Fig 23.17

(“one on bottom”)(“one on bottom”)

FootwallFootwall

B. Types of faultsB. Types of faults2. 2. Hanging wallHanging wall-- Fig 23.17Fig 23.17

(“one on (“one on top”)top”)

V. Vertical movement V. Vertical movement along a faultalong a fault

1. 1. Reverse FaultReverse Fault-- Fig 23.18Fig 23.18- - Footwall Footwall down down

Examples:Examples: Rocky MountainsRocky Mountains Canadian RockiesCanadian Rockies Appalachian Mts.Appalachian Mts.

V. Vertical movement along V. Vertical movement along a faulta fault

2. 2. Normal FaultNormal Fault-- Fig 23.19Fig 23.19- - Footwall upFootwall up

VI. Horizontal movement VI. Horizontal movement along a fault boundary (Fig. along a fault boundary (Fig.

23.22)23.22)A.A. Transform-fault boundaryTransform-fault boundary – – plates are plates are sliding past one anothersliding past one another (Figs. 23.27 & 28)(Figs. 23.27 & 28)

E.g. San Andreas fault in E.g. San Andreas fault in CaliforniaCalifornia

★ ★ Earthquakes caused by Earthquakes caused by sheering forcessheering forces

B. B. Divergent BoundariesDivergent Boundaries1. two plates are 1. two plates are moving apartmoving apart

(Fig. 23.23) (Fig. 23.23) Plate APlate A Plate BPlate B

2.2. Creates Creates rift valleysrift valleys – – large spreading valleys large spreading valleys at fault lineat fault line 33.. Creates Creates sea floor spreadingsea floor spreading-- a rift valley on sea floora rift valley on sea floor 4. Caused by 4. Caused by tensional forcestensional forces

B. B. Divergent BoundariesDivergent Boundaries

C.C. Convergent Convergent BoundariesBoundaries

1. Two plates 1. Two plates move towards each move towards each otherother (Fig 23.24)(Fig 23.24)

Plate APlate A Plate BPlate B2. Leads to 2. Leads to subductionsubduction- one plate - one plate (usually oceanic crust) (usually oceanic crust) goes goes beneathbeneath the other the other (continental crust). (continental crust).

Caused by Caused by compressional forcescompressional forces

C.C. Convergent Convergent BoundariesBoundaries

C.C. Convergent Convergent BoundariesBoundaries

E. g. Andes Mountains in S. AmericaE. g. Andes Mountains in S. America (Still growing because of (Still growing because of

subduction)subduction)

3. ★3. ★Common place to find volcanoesCommon place to find volcanoes

E.g. Cascade Range E.g. Cascade Range (Mt. St. Helens, (Mt. St. Helens, Mt. Rainier…)Mt. Rainier…)

Tectonic Plate MovementTectonic Plate Movement

Major Tectonic PlatesMajor Tectonic Plates