Earth’s Interior. Essential Questions What are the layers of the Earth? What is the lithosphere, asthenosphere, and mesosphere? What is an earthquake?

Earth’s Interior

Essential Questions

• What are the layers of the Earth?• What is the lithosphere, asthenosphere, and

mesosphere?• What is an earthquake?• What is the way to detect an earthquake?• What are the ways to prepare for an

earthquake?

What are the layers of the Earth?

Bill Nye…..

• While watching the video complete your movie worksheet. This is to be put into your portfolio.

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• 24mins

Layers of the EarthOceanic crustContinental crust

Upper mantle

Transition region

Lower mantle

D“

Outer core

Inner core

Layers of the Earth continued…• Inner core: – 1.7% of the Earth's mass– depth of 5,150-6,370 kilometers – unattached to the mantle, suspended in the

molten outer core– is solid iron-nickel alloy – is hotter than the outer core, may have a

temperature up to about 13,000°F (7,200°C = 7,500 K), but the intense pressure keeps it solid

• Outer core: – 30.8% of Earth's mass– depth of 2,890-5,150 kilometers – is composed of an iron-nickel alloy– is a hot, electrically conducting liquid

Layers of the Earth continued…• D":

– 3% of Earth's mass– depth of 2,700-2,890 kilometers Although it is often identified as part of the lower mantle, seismic

discontinuities suggest the D" layer might differ chemically from the lower mantle lying above it.

• Lower mantle: – 49.2% of Earth's mass– depth of 650-2,890 kilometers– is probably composed mainly of silicon, magnesium, and oxygen. It

probably also contains some iron, calcium, and aluminum. • Transition region:

– 7.5% of Earth's mass– depth of 400-650 kilometers – is dense when cold because of the garnet. It is buoyant when hot

because these minerals melt easily to form basalt which can then rise through the upper layers as magma.

Layers of the Earth continued…• Upper mantle:

– 10.3% of Earth's mass– depth of 10-400 kilometers

• Oceanic crust: – 0.099% of Earth's mass– depth of 0-10 kilometers – the majority of the Earth's crust was made through volcanic activity.

• Continental crust: – 0.374% of Earth's mass– depth of 0-50 kilometers – is the outer part of the Earth composed essentially of crystalline rocks.

Time to pause….

• In your portfolio answer the following question:– We often hear the Earth referred to as solid.

With the information you now have explain if this is true or false.

What is the lithosphere, asthenosphere, and mesosphere?

Earth’s Structural Zones

• The Earth is divided into 5 structural zones:– Lithosphere– Asthenosphere– Mesosphere– Outer Core– Inner Core

• We have already reviewed the outer and inner core.

Lithosphere• It's very stiff, and fractures if you push too hard

• The lithosphere is part of the crust and the upper mantle.

• The prefix "lithos" is Greek for "stone" or "rock." • This layer is solid and the most rigid of the other

layers. • It is about 15 to 300 kilometers thick.

Asthenosphere• It's hot and flows like molasses

• The asthenosphere lies below the lithosphere. • Its prefix "asthenes" is Greek for the word "weak.“– Keep in mind; it is not as weak as a brittle piece of wood.

However, it is weaker than the other layers.

• This layer is about 200 kilometers thick • It contains hotter, softer rock that flows like lava.

Mesosphere

• The mesosphere or "middle layer" is found at the lower part of the mantle.

• Scientists believe it is solid rock.

So how do scientists know this?• Geophysical surveys: seismic, gravity,

magnetics, electrical, geodesy– Acquisition: land, air, sea and satellite– Geological surveys: fieldwork, boreholes, mines

• What are seismic waves?• When a sudden break or shift occurs in the earth's

crust, the energy radiates out as seismic waves.• There are 2 categories of seismic waves:

– Body waves– Surface waves

What is an earthquake?

Bill Nye - Earthquakes

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Body waves• Move through the inner part of the earth • There are 2 types of body waves

– Primary waves, also called P waves or compressional waves• P waves arrive first at any surface location• can travel through solid, liquid and gas• are waves that have the same direction of vibration along their direction

of travel, which means that the vibration of the medium (particle) is in the same direction or opposite direction as the motion of the wave

• As they travel through rock, the waves move tiny rock particles back and forth -- pushing them apart and then back together

• http://www.geo.mtu.edu/UPSeis/images/P-wave_animation.gif– Secondary waves, also called S waves or shear waves

• As these waves move, they displace rock particles outward• S waves don't move straight through the earth• only travel through solid material • the ground is displaced perpendicularly to the moves alternately to one

side and then the other • http://www.geo.mtu.edu/UPSeis/images/S-wave_animation.gif

Surface Waves• sometimes called long waves, or simply L wave• are responsible for most of the damage associated

with earthquakes, because they cause the most intense vibrations

• stem from body waves that reach the surface• are something like the waves in a body of water --

they move the surface of the earth up and down• L waves are the slowest moving of all waves

P and S waves

• Both P and S waves refract or reflect at points where layers of differing physical properties meet. They also reduce speed when moving through hotter material. These changes in direction and velocity are the means of locating discontinuities.

• Seismic discontinuities (a surface at which velocities of seismic waves change abruptly) aid in distinguishing divisions of the Earth into inner core, outer core, D", lower mantle, transition region, upper mantle, and crust (oceanic and continental).

Earthquakes

• Did you know…– According to the United States Geological Survey,

more than three million earthquakes occur every year. That's about 8,000 a day, or one every 11 seconds!

What is the way to detect an earthquake?

Detection• Detecting an earthquake is much easier than

predicting one. – a powerful earthquake can be felt by people in the area,

and the damage it causes can be seen.

• A machines, known as seismometers, or seismographs, is used– they can record the movements automatically, – they work on a simple principle; that a heavy weight

suspended on a wire will remain steady as the vibrations pass, whilst the frame holding it will be vibrated.

Reading a Seismogram

• When you look at a seismogram, there will be wiggly lines all across it. These are all the seismic waves that the seismograph has recorded.

• Most of these waves were so small that nobody felt them.

Reading a Seismogram continued• The P wave will be the first wiggle that is bigger than the rest

of the little ones (the microseisms). – Because P waves are the fastest seismic waves, they will usually be the

first ones that your seismograph records. • The next set of seismic waves on your seismogram will be the

S waves. – These are usually bigger than the P waves.– If there aren't any S waves marked on your seismogram, it probably

means the earthquake happened on the other side of the planet. S waves can't travel through the liquid layers of the earth so these waves never made it to your seismograph.

• The surface waves are the other, often larger, waves marked on the seismogram. – They have a lower frequency. – Surface waves travel a little slower than S waves.

Finding the Epicenter• Measure the distance between the first

P wave and the first S wave. In this case, the first P and S waves are 24 seconds apart.

• Find the point for 24 seconds on the left side of the chart below and mark that point. According to the chart, this earthquake's epicenter was 215 kilometers away.

• Measure the amplitude of the strongest wave. The amplitude is the height (on paper) of the strongest wave. On this seismogram, the amplitude is 23 millimeters. Find 23 millimeters on the right side of the chart and mark that point.

• Place a ruler (or straight edge) on the chart between the points you marked for the distance to the epicenter and the amplitude. The point where your ruler crosses the middle line on the chart marks the magnitude (strength) of the earthquake. This earthquake had a magnitude of 5.0.

The Richter Scale• The Richter Scale is the best known scale for

measuring the magnitude of earthquakes. • The energy released by an earthquake increases by

a factor of 30 for every unit increase in the Richter scale.

• An earthquake that measures 4.0 on the Richter scale is 10 times larger than one that measures 3.0

Richter scale no. No. of earthquakes per year

Typical effects of this magnitude

< 3.4 800 000Detected only by

seismometers

3.5 - 4.2 30 000Just about noticeable

indoors

4.3 - 4.8 4 800Most people notice them,

windows rattle.

4.9 - 5.4 1400Everyone notices them,

dishes may break, open doors swing.

5.5 - 6.1 500Slight damage to buildings,

plaster cracks, bricks fall.

6.2  6.9 100Much damage to buildings:

chimneys fall, houses move on foundations.

7.0 - 7.3 15Serious damage: bridges

twist, walls fracture, buildings may collapse.

7.4 - 7.9 4 Great damage, most

buildings collapse.

> 8.0 One every 5 to 10 yearsTotal damage, surface

waves seen, objects thrown in the air.

What are the ways to prepare for an earthquake?