Dynamic Earth

Part 1. Uplift

A. Rising of the Earth’s crust

B. Evidence1. Fossils of seashells in rocks on a

mountain

2. Observing sedimentary rock layers

I. Uplift

Faulted Layers

Tilted Layers

Folded Layers

Normal Layers

Part 2. Earthquake

A. Vibrating, shaking or rapid motion of the Earth’s crust

B. Terms1. Focus – point where the break (fault)

happens

2. Epicenter – point on surface directly OVER the focus; EQ is strongest here

II. Earthquake3. Intensity – measure of the damage

caused by EQ

4. Magnitude – total energy released by EQ

5. Seismic Waves – energy waves sent through Earth during an EQ

6. Seismograph – used to record seismic waves and determine the magnitude of the EQ

II. Earthquake

II. EarthquakeC. Richter Scale – used to measure

energy of an EQ1. Each number shows increase of 10 times

EarthquakeD. Seismic Waves

1. P-Waves – primary waves; fastest moving; travel through solids AND liquids; particles move in same direction of travel

2. S-Waves – shear or secondary waves; slower than P; CANNOT travel through liquids; particles move in right angles to direction

3. The more dense the

material, the faster

the waves move

II. Earthquake

Notice the vertical axis

This represents TIME (in minutes!)

Let’s enlarge a small section

Prepared by Mr. DeMarco

Between each minute, we notice that there are 3 segments.

If there are 60 seconds in a minute, each one of these segments must be ________seconds.

Prepared by Mr. DeMarco

What would this time be?

Prepared by Mr. DeMarco

Notice the horizontal axis

This represents DISTANCE (in thousands of

Kilometers!)

Let’s enlarge a small section

Prepared by Mr. DeMarco

Prepared by Mr. DeMarco

There are also two curves on this chart that display the way different earthquake waves behave.

Prepared by Mr. DeMarco

Prepared by Mr. DeMarco

This chart can be used for answering many different questions!

How long does it take an S-Wave to travel 5,000km?

Prepared by Mr. DeMarco

Prepared by Mr. DeMarco

The recording station tells us it took 6 minutes and 20 seconds for the P-Wave to reach them. How far away from the epicenter of the earthquake must they be?

Prepared by Mr. DeMarco

Prepared by Mr. DeMarco

I know that there was a 7 minute difference in the arrival of my P and S waves. How far away from the epicenter must I be?

Prepared by Mr. DeMarco

Mark off 7 minutes on scrap paper…

Slide your scrap paper up until the tick marks match up with the curves…

Prepared by Mr. DeMarco

Part 3. Finding Epicenter Distance

A. P-Wave arrives at 3:21

B. S-Wave arrives at 3:25

C. Difference in arrival times = 4 minutes

D. Using EQ chart…1. Epicenter Distance = 2.6x103 = 2600 km

Part 4. Finding Origin Time

A. Origin Time – when EQ happens1. Find Epicenter Distance first (2600 km)

2. Use EQ chart to find a P-Wave travels 2600 km in 5 minutes

3. P-Wave Time – Travel Time = Origin Time

4. 3:21 – 5 minutes = 3:16 Origin Time

IV. Finding Origin Time

A. Example1. P-Wave arrived @ 5:35

2. S-Wave arrived @ 5:41

3. What time did EQ happen?

4. Difference = 6 minutes

5. Epicenter Dist = 4400 km

6. P-wave Travel Time = 7 min 40 sec

7. 5:35:00 – 00:07:40 = ?

8. 5:27:20

V. Locating an Epicenter

A. 3 seismographs are needed to locate an epicenter.

V. Locating an EpicenterB. Example

1. Station A = 2500 km

2. Station B = 1500 km

3. Station C = 500 km

A

C

B

Epicenter

Part 1. Layers of Earth

A. Using Seismic waves, models have been made for Earth’s interior

1. Between 5 and 60 miles there is a sudden increase in speed of the waves

a. So density increases between 5 and 60 miles

b. This boundary is called Mohorovicic Discontinuity (Moho)

Layers of Earth

B. Crust (Lithosphere)1. Less dense rock above the Moho; 5-60

miles thicka. Continental Crust – THICKEST under

continents; less dense; granite rock

b. Oceanic Crust – THINNEST under oceans; more dense; basalt rock

Layers of Earth

Layers of Earth

C. Mantle1. More dense rock below the Moho;

extends to 2900 km deepa. Asthenosphere – upper level of mantle;

moves and contains convection currents

b. Stiffer mantle – more dense and solid under the asthenosphere

Layers of Earth

D. Core1. Outer Core – probably liquid; S-Waves

do NOT travel through this region

2. Inner Core – very center of Earth; acts like a solid due to extreme pressure

3. Core mainly made of iron and nickela. Learned from studying meteorites

Layers of Earth

Convection Currents

Depth in km

Pressure (1atm is pressure at surface)

Temperature

Densities

(continental < oceanic)

Melting Occurs HERE!

What is the pressure found at 3000 km?

1.5 million atm

What is the temperature found at 2000 km?

4200 ° C

Part 2. Shifting of the CrustA. Continental Drift Theory

1. Proposed by Alfred Wegner in 1912

2. Continents had been moving for millions of years

Shifting of the Crust3. Evidence

a. Continents seem to fit together (Pangea)b. Rock layers match on edges of continentsc. Similar fossils found along continental edges

4. Did NOT explain WHY they moved

Shifting of the Crust

B. Sea Floor Spreading 1. Chain of underwater mountains found

near center of Atlantic Ocean (mid-Atlantic Ridge)a. Rock at center is YOUNGER than outside

rock

b. Higher temps found in rock along ridge

Shifting of the Crust

Shifting of the Crust

c. Center of ridge is a deep, steeply walled valley

d. Molten rock is pushed to surface, causing sea floor to spread (widen) as ocean is pushed apart along the ridge

Shifting of the Crust

2. Paleo-magnetism – the switching of the magnetic poles follows a pattern that matches up on each side of the ocean ridges

Shifting of the Crust

Part 3. Plate Tectonics

A. Plates – rigid moving pieces that make up the crust of Earth; 12 major plates

B. As plates move, continents are carried with them

C. Plates are moved by convection currents within upper mantle (asthenosphere)

Plate Tectonics

Plate Tectonics

D. Plate Boundaries1. Types

a. Divergent – plates moving away from each other; mid-ocean ridges

b. Convergent – plates colliding with one plate sinking under the other; ocean trenches (subduction)

c. Transform – plates sliding past each other; San Andreas Fault

2. Most active areas of the crust (location of most EQs, volcanoes and mountain building)

Plate Tectonics