Y9 Physics - Probing Poabet Earth

Earth’s structure (Thé Earth…properties)

The Earth is made of layers with different properties

Crust (Thé…layer…Earth)

The thin outer layer of the Earth

MantleThe…beneath the crust…rock)

The thick layer beneath the crust made of semi-molten rock

Core (Thé central…iron nickel)

The central part of the Earth made mainly of iron and nickel

Outer core

The liquid layer of the core

Inner core

The solid central part of the core

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Seismic waves (waves of energy…earthquakes…earth

Waves of energy released by earthquakes that travel through the Earth

Earthquake (A sudden…releases energy)

A sudden movement of the Earth’s crust that releases energy

Focus

The point inside the Earth where an earthquake starts

Epicentre

The point on the Earth’s surface directly above the focus

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P-waves (primary waves)

Longitudinal seismic waves that can travel through solids and liquids

S-waves (secondary waves) (Transverse …that can only…solids)

Transverse seismic waves that can only travel through solids

P-wave speed

Faster than S-waves

S-wave speed

Slower than P-waves

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Evidence for Earth’s structure

Based on how seismic waves travel through the Earth

S-waves and the core

S-waves do not travel through the outer core, showing it is liquid

P-waves and the core P waves change…different layers)

P-waves change speed and direction, showing different layers

Shadow zone

An area where no seismic waves are detected

P-wave shadow zone

Caused by refraction of P-waves in the core

S-wave shadow zone (caused because)

Caused because S-waves cannot travel through liquid outer core

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Refraction (seismic waves) (Thé change…speed)

The change in direction of a wave when its speed changes

Wave speed and density Seismic…changes…changes)

Seismic wave speed changes when density changes

Boundary between layers (Causes…waves)

Causes refraction of seismic waves

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Using seismic data (Scientists…times…paths…structuRe)

Scientists use travel times and paths of waves to infer Earth’s structure

Indirect evidence

Evidence gathered without direct observation

Direct evidence (Earth) (Very…only…crust)

Very limited because drilling only reaches the crust

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Model of Earth

A simplified representation of Earth’s internal structure

Strength of Earth model (Explains)

Explains seismic wave behaviour

Limitation of Earth model (Based on)

Based on indirect evidence, not direct observation

Impacts of p waves on the ground/materials

Causes the ground/materials to expand and compress

Impacts of S waves on the ground/materials

Causes the ground/materials to shake side to side

Factors to consider

Wave type, wave speed, wave media, wave constant refraction (mostly), scientific observations

How seismic waves are used to predict structure

Change speed and direction constantly, S waves can’t travel through liquid evidence for outer core, p wave refraction shadow zones - boundary locations, used to map earths internal layers.