Lesson 1:

What are earthquakes and where do they

occur

Where do Earthquakes Occur?

• Earthquakes can occur near the Earth’s surface or far below the surface.

• Most earthquakes occur at plate boundaries, but some happen at faults located in the middle of tectonic plates.

PLATE BOUNDARIES

Earthquake Locations Around the World

What Causes Earthquakes?• Earthquakes are caused by movement along

faults.• When stress is placed on rocks it deforms, or

changes.• Rock is stretched and bent until it can no longer

take the stress.• When enough stress builds up in the rock it, it

slips and energy is released.• This energy is felt as an earthquake.

Earthquakes in St Louis??Earthquakes in St Louis??

Do we live near a plate boundary?Do we live near a plate boundary?

Do we live near a fault?Do we live near a fault?

The New Madrid FaultThe New Madrid Fault If there is no plate boundary in the middle of the If there is no plate boundary in the middle of the

United States, why did these earthquakes take place? United States, why did these earthquakes take place? Geologists are beginning to understand the answer. Geologists are beginning to understand the answer.

The New Madrid Fault Zone is part of an The New Madrid Fault Zone is part of an ancientancient plate plate boundary. In this area, the North American Plate tried boundary. In this area, the North American Plate tried to form a divergent plate boundary about 500 million to form a divergent plate boundary about 500 million years ago. The splitting stopped before new plates years ago. The splitting stopped before new plates could form. The faults in the New Madrid Zone are could form. The faults in the New Madrid Zone are remnants of this old event. Earthquakes occur because remnants of this old event. Earthquakes occur because the North American Plate is still "settling down". The the North American Plate is still "settling down". The faults in the New Madrid Zone do not reach the Earth’s faults in the New Madrid Zone do not reach the Earth’s surface. They are buried beneath thousands of feet of surface. They are buried beneath thousands of feet of rock and sediment deposited by the Mississippi River. rock and sediment deposited by the Mississippi River. Geologists have located them by looking at the Geologists have located them by looking at the patterns of earthquakes in the zone. patterns of earthquakes in the zone.

Several of the Several of the largest earthquakes largest earthquakes ever recorded in the ever recorded in the

United States United States occurred in the occurred in the

Midwest, far from Midwest, far from any plate boundary. any plate boundary. These earthquakes These earthquakes

took place in an area took place in an area called the New called the New

Madrid Fault Zone, Madrid Fault Zone, named after the named after the

town of New Madrid, town of New Madrid, Missouri.Missouri.

New Madrid FaultNew Madrid Fault

Over a three-month period in the Over a three-month period in the winter of 1811 to 1812, the New winter of 1811 to 1812, the New Madrid Fault Zone was struck by Madrid Fault Zone was struck by three huge earthquakes estimated to three huge earthquakes estimated to be greater than magnitude 8.0 be greater than magnitude 8.0

The New Madrid Fault is what causes The New Madrid Fault is what causes Alabama to experience earthquakes.Alabama to experience earthquakes.

3 Types of Faults associated with Earthquakes

PLATE MOTION FAULT TYPE

Transform Strike –Slip Fault

Convergent Reverse Fault

Divergent Normal Fault

Strike-Slip Fault occurs at a Transform Boundary

Reverse Fault occurs at a Convergent Boundary

Normal Faults occur at Divergent Boundaries

How do Earthquake Waves Travel?How do Earthquake Waves Travel?

Energy releasedEnergy released from moving from moving plates and faultsplates and faults travels travels through through the Earth the Earth as wavesas waves..

These waves are These waves are called seismic called seismic waveswaves..

Types of Seismic WavesTypes of Seismic Waves

1. 1. BODY WAVESBODY WAVES:: Seismic waves that travel Seismic waves that travel through the Earth.through the Earth.

2. 2. SURFACE WAVESSURFACE WAVES:: Seismic waves that travel Seismic waves that travel along the surface.along the surface.

WAVES TRAVEL:WAVES TRAVEL:

1.1.At different speedsAt different speeds and and

2 2 In different waysIn different ways

Depending on what kind of material Depending on what kind of material they are moving through.they are moving through.

Seismic Wave Arrival• First- P-waves

• Second- S-waves

• Third- Surface Waves

Quiz• 1. Most Earthquakes occur along ________________.• 2. The first seismic waves to arrive are______________.• 3. The second seismic waves to arrive are

_____________.• 4. The last seismic waves to arrive are_______________.• 5. Which seismic waves travel the fastest?___________• 6. Which type of seismic wave can move through a

solid, liquid or a gas?________________• 7. Which seismic wave cannot travel through material

that is completely liquid?______________• 8. Which seismic waves are the slowest and the most

destructive?_______________

Seismograph• A seismograph is an instrument used by scientists to measure

earthquakes.• Seismologists who study earthquakes can determine when an

earthquake started by noting the arrival times of P-waves and S-waves.

• A seismograph records vibrations in the Earth and determines the strength and location of an earthquake.

Ancient Chinese Seismograph. The ball would drop from the dragon to the frog. It told the people which direction the earthquake come from.

SeismogramsSeismograms

Time in Minutes0 1 2 3 4 5 6 7 8

1. How many minutes did it take for the

P-Waves to arrive?

2. How many minutes did it take for the

S-waves to arrive?

3. How long did the surface waves last?

Epicenter• The epicenter is the point on the

Earth’s surface directly above an earthquake’s starting point.

Focus• The focus is the point inside the

Earth where the earthquake begins.

• The epicenter is located directly above the focus.

Volcanoes form around

vents that release magma onto the Earth’s surface.

Vents

Lava

Magma chamber

The Composition of Magma Determines whether it is explosive or not!

High water contentHigh water content• More likely to beMore likely to be !!!!!!

High High content content• More likely to be More likely to be !!!!!!• WhyWhy??

Silica has a thick, stiff consistencySilica has a thick, stiff consistency• Flows slowlyFlows slowly• Tends to Harden in the volcano’s ventTends to Harden in the volcano’s vent

a. What physical event causes explosive a. What physical event causes explosive eruptions?eruptions?

b. Would high water content increase the b. Would high water content increase the likelihood of having an explosive eruption?likelihood of having an explosive eruption?

c. Would high silica content increase the c. Would high silica content increase the likelihood of having an explosive eruption?likelihood of having an explosive eruption?

Quiz Part 2

What Erupts from a Volcano?

Lava can be thick or thin.

Blocky lava

PahoehoeAa

Pillow lava

Types of Volcanoes

Shield volcano

Cinder cone volcano

Composite volcano

What causes volcanoes?

The Formation of Magma• Mantle rock melts when the temperature increases or the pressure decreases.

What causes volcanoes?

Where Volcanoes Form• Tectonic Plate Boundaries!!!

~75% world’s active volcanoes in Ring of Fire

What causes volcanoes?

What causes volcanoes?

Hot Spots

Measuring Small QuakesMeasuring Small Quakes• Before eruption, increase in number & Before eruption, increase in number &

intensityintensity Measuring SlopeMeasuring Slope

• Bulges may form with magma (tiltmeter)Bulges may form with magma (tiltmeter) Measuring Volcanic GasesMeasuring Volcanic Gases

• Outflow of volcanic gasesOutflow of volcanic gases Sulfur dioxide, carbon dioxideSulfur dioxide, carbon dioxide

Measuring Temperature from OrbitMeasuring Temperature from Orbit• Measure changes in temperature over timeMeasure changes in temperature over time

How do volcanologists predict How do volcanologists predict eruptions?eruptions?

You should not be a You should not be a Volcanologist if….Volcanologist if….

You don’t like You don’t like hiking, hiking, backpacking, backpacking, rock climbing, rock climbing, etc.etc.

You are not You are not interested in interested in experiencing experiencing extreme extreme temperatures temperatures and heights.and heights.

If you don’t like If you don’t like to travel to to travel to incredible incredible places and see places and see breathtaking breathtaking views of the views of the world.world.

Robert McGimsey USGS

A. Ozerov