Earthquakes and

Volcanoes Amole

Spectra

2013

Earthquakes

What are ?

• The resulting vibrations that occur from rocks sliding past one another at a fault

• Caused by pressure experienced at plate boundaries

• Energy is released as seismic waves• Seismic waves create the “shaking”

The Ring of Fire

Earthquake Features• Focus- exact point

inside Earth where quake originates

• Epicenter- Point on surface directly above focus

• Energy travels outward from these points in the form of waves

Types of Seismic Waves

• Primary or P waves-– Longitudinal– From focus– Fastest (arrives first)

• Secondary or S waves-– Transverse wave– From focus– Slower (arrives second)

• Surface waves or L waves-– Circular motions

• Up and down• Back and forth

– From epicenter– Moves across surface– Slowest (arrives last)– Most destructive

Measuring Earthquakes• Three Seismograph• Difference between arrival

times allows seismologists to calculate the distance to the epicenter

• Draw three circles with radii being the distance to epicenter.

• The overlapping is the location of the epicenter

Measuring Earthquakes• The Richter Scale is used to measure the

energy (magnitude) of the earthquake• Does not predict severity/damage

– Building construction– Depth of focus– Soil composition and saturation– Type of rock

• Mercalli scale rates the quakes effect of surface (intensity)

Magnitude Earthquake Effects Estimated NumberEach Year

2.5 or less Usually not felt, but can be recorded by seismograph.

900,000

2.5 to 5.4Often felt, but only causes minor

damage. 30,000

5.5 to 6.0 Slight damage to buildings and other structures.

500

6.1 to 6.9 May cause a lot of damage in very populated areas.

100

7.0 to 7.9Major earthquake. Serious

damage. 20

8.0 or greaterGreat earthquake. Can totally destroy communities near the

epicenter.

One every 5 to 10 years

Richter Scale

7.8 magnitude (China)

San Francisco, 1906

Alaska Earthquake 1964

Tsunamis are Ocean Earthquakes

Seismic Waves and Earth’s Interior

Fact Observation Theory

Waves change speed and

direction when the density of the

medium changes

Velocity of seismic waves are

different t different locations

The Earth is composed of

different layers containing

different materials

S waves are transverse and

cannot pass through liquids

S waves do not reach the side of

Earth’s core opposite the focus

Part of the Earth’s core must be liquid

• Seismic waves can be used to investigate the Earth’s interior.

http://www.pbs.org/wnet/savageearth/animations/earthquakes/

What is a Volcano?• An opening in Earth’s crust through which

magma has reached the Earth’s surface• Release molten rock, ash, and gases• Often form hills or mountains as lava builds and

cools• Generally have one central vent• Magma that reaches the surface is called lava• Most occur at convergent plate boundaries

The Ring of Fire

Types of Volcanoes

• Shield • Composite• Cinder Cones

• Seamounts• Hot spots

Shield Volcanoes

• Magma rich in iron and magnesium

• Flows great distances

• Mild and frequent eruptions

• Gentle slopes• Some of the largest

Shield Volcanoes

Mauna Loa, Hawaii

Composite Volcanoes• Alternating layers of

ash, cinder, and lava• Magma rich in silica• Trapped gases cause

eruptions that alternate between flows and explosions of cinder and ash

• Steeper slopes

Composite Volcanoes

Mt. Vesuvius, Italy

Mt. Rainer, Washington

Cinder Cone Volcanoes• Smallest and most

abundant• Violent eruptions due

to large amounts of trapped gas

• Only active for short time

• Steepest slopes

Cinder Cone

Paricutin, Mexico

Underwater Volcanoes

• Called seamounts• Look like composite

volcanoes• Occur at divergent

plate boundaries

Hot Spots• Occur in the middle of plates• Mantle plumes melt as the rise from the

mantle and erupt• Mantle plumes under oceans create

islands from ash and lava that builds up and breaks through the surface

• As the plate moves the mantle plume stays creating a chain of extinct volcanic islands

The Hawaiian Islands