Seismic Waves Surface Waves - PowerPoint Presentation

Slide1
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Seismic Waves

Surface Waves

Seismic

Waves

are shock

waves

given off by earthquakes.

There are 2 types:

1. Body Waves originate from the focus (F)travel through the earth. They’re used to locate epicenters (E.)

E

FSlide3

2 Types of Body Waves

Surface Waves

Primary

(P) Waves

–

compression

waves

travel

fastest

through solids first waves to arriveSecondary (S) Waves shear wavescannot travel through liquidssecond to arriveonly half as fast as P waves

E

FSlide4

2 Types of Body Waves

P Waves

–

Compressional (or Longitudinal)

Waves

2) S Waves

– Shear WavesSlide5

Seismic Waves

Surface Waves

Seismic

Waves

are shock

waves

given off by earthquakes.

There are 2 types:

Surface Waves (also called L (Long) Waves) Start forming when body waves reach the surface at the epicenter,They arrive much later than body waves.

E

FSlide6

Seismology

Seismic Body Waves and the Earth’s InteriorSlide7

S Waves do not

travel through

liquids

.Slide8

S Waves do not

travel through the

outer

core.Slide9

The

outer core

must be

liquid

.Slide10

P waves slow down in the

outer

core and then

speed up in the

inner core.Slide11

Bending of P Waves Creates Two

S

mall “Shadow Zones”Slide12

P Wave Travel Paths

P Wave Direction

P Wave

Wave

FrontsSlide13

Conclusion:The inner core

must be

solid

.Slide14

Two Shadow Zones

Note:

S Waves

are totally blocked by the

outer core, so they have a

huge shadow zone.Slide15

Seismic Waves and Earth Layers

Seismic Waves travel

faster

through

cold, dense rock and slow down

traveling through warm, less dense

rock.Slide16

Seismic Waves and Earth Layers

There is a

sharp rise

in

wave speed

between the crust and mantle

and again between the mantle and the outer core. Slide17

Seismic Waves and Earth Layers

These sudden changes in wave speed are due to

sharp changes

in the

type

and density of rock which are called discontinuities. Slide18

Mohorovičić Discontinuity (Moho

)

Andrija

Mohorovičić

Sharp boundary between the

crust

and

upper mantleSlide19

When you get a

CT scan

(

Computerized Tomography Scan

), the machine records your body image in a series of “slices”…Slide20

Computerized Tomography

…which the computer puts together into a detailed

3-D image

of your body’s soft tissue and internal organs.Slide21

Seismic Tomography

Geophysicists use a similar technique with hundreds of seismic stations worldwide to make a

3 – D seismic tomographic image:Slide22

Layers of the Earth

Basic seismology told us that Earth has four main layers.Slide23

4 Earth Layers*

Seismic Tomography allows us to see smaller details in Earth’s structure that we didn’t know about before.Slide24

4 Earth Layers* - Plus One

There are 4 main layers…

*plus

another:

The

D” layer

is a thin layer in the lower 100 km of the lower mantle.

The Core/Mantle boundary is very

rugged and mountainous. Slide25

Anti-Continents and Anti-Oceans

Solid Mantle

Liquid Iron Outer Core

“Anti-Continents”

“Anti-Oceans”Slide26

2 More Boundary Layers (Discontinuities) below the

Moho

1)

2)

3)Slide27

Ultra-Low Velocity Zone (ULVZ)

A soft “squishy “ region found along the D” Core/Mantle Boundary is called the

U

ltra-

L

ow Velocity Zone (ULVZ

).(Seismic waves slow way down.)Slide28

Core-Mantle BoundarySlide29

D” Layer – Bottom 100 km of MantleSlide30

Mantle “Blobs”

Hot Blobs are less dense and rise towards the surface.

Cold Blobs are more dense and sink lower in the mantle.Slide31

Tomogram and Topographic Map - Mantle Blobs

Bring up QuickTimeSlide32

Tomograms of Mid and Deep Mantle

Red

– hot light rock

Blue – cold heavy rockSlide33

Tomograms of Mid and Deep Mantle

Red

– hot light rock

Blue – cold heavy rockSlide34

Mantle Blobs and Gravity Anomalies

Satellite bobs up

Satellite bobs downSlide35

Tomographic Map of Japan and ChinaSlide36

Cross-Section across Japan and China

Blue

- heavy

rock:

Sinking ocean crust

“flattens out” at 500 km and then eventually continues to

sink into the lower mantle.Slide37

Tomogram of Pacific Ocean Crust and Mantle

Brown

=

warm,

light rock Blue = cold, heavy rockSlide38

World Tomogram

Blue

blobs show

heavy sinking slabs of crust.Red

blobs show warm, rising blobs of rock.Slide39

“Convection Plumes”

Hot

, less dense plumes

rise

up, while

cold

, denser plumes sink in a circular motion called convection.Slide40

“Convection Plumes”

Hot

, less dense plumes

rise

up, while cold, denser plumes sink in a circular motion called

convection.Slide41
Slide42

Surface Waves

Love

Waves -

Horizontal

shear

Rayleigh

Waves

–

Vertical shear

The combined effect of horizontal and vertical shear is to wrench buildings and highways apart.