Faults, Earthquakes & Volcanoes

Faults

Surface along which rocks move when they pass their elastic limit and break

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Earthquake

Vibrations produced when rocks break along a fault

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Normal Fault

Break in rock caused by tension forces, where rock above the fault surface moves down relative to the rock below

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Reverse Fault

Break in rock caused by compressive forces, where rock above the fault surface moves upward relative to the rock below

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Strike-Slip Fault

Break in rock caused by shear forces, where rocks move past each other without much vertical movement

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Primary (P) – wave

Seismic wave that moves rock particles back-and-forth in the same direction that the wave travels

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Secondary (S) – wave

Seismic wave that moves rock particles at right angles to the direction of the wave

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Whose FAULT is it?

• STRIKE-SLIP– Side-to-side motion– Happens at TRANSFORM boundaries– Ex. San Andreas Fault

Fault Surface

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Whose FAULT is it?

• NORMAL– Hanging wall moves down– Happens at DIVERGENT boundaries

Fault Surface

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Whose FAULT is it?

• REVERSE (aka THRUST)– Hanging wall moves up– Happens at CONVERGENT boundaries

Fault Surface

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Earthquakes!

• A seismic wave is a wave generated by an earthquake. • There are 3 types of waves:–Primary waves (P-waves)–Secondary waves (S-waves)–Surface waves

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Seismic Waves

• http://www.classzone.com/books/earth_science/terc/content/visualizations/es1002/es1002page01.cfm

Earthquakes!

• Focus is the point BELOW the Earth’s surface where seismic waves start• Epicenter is the point on earth’s

SURFACE directly above the focus

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Earthquakes!

• Liquefaction occurs when wet soil acts more like a liquid during an earthquake

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Earthquakes!

• Tsunami is a seismic sea wave that begins over an earthquake focus and can be destructive when it hits the shore

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What is an Earthquake like?

• Earthquake Montage: http://video.nationalgeographic.com/video/environment/environment-natural-disasters/earthquakes/earthquake-montage/

• Earthquake in Japan: http://www.youtube.com/watch?feature=player_embedded&v=x9QNzGY0qxw#

• Japan Tsunami:• http://

nctr.pmel.noaa.gov/honshu20110311/20110311Houshu.mov

Where do they occur?

• http://earthquake.usgs.gov/earthquakes/map/

Earthquake Facts59

Inner core

Outer core

Mantle

CrustFOCUS

EPICENTER

Surface wave

P-wave

S-wave

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Earthquake Facts

• An earthquake is the vibration, sometimes violent, of the Earth’s surface that follows a release of energy in the Earth’s crust

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Earthquake Facts

• P-waves push tiny particles of Earth material directly ahead of them or displace the particles behind their line of travel.

• Only P-waves travel through the Earth’s molten core.

How do we know?

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Earthquake Facts

• S-waves displace materials at right angles.

• They cannot move through the core and are slower than P-waves

How do we know?

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Earthquake Facts

• Surface waves, which travel along the Earth’s surface, create the most noticeable damage (they are the slowest)

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Measuring an Earthquake

• The vibrations produced by earthquakes are detected, recorded, and measured by instruments called a seismograph

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Measuring an Earthquake

• We need 3 seismograph station readings to find the focus and epicenter of an earthquake

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Measuring an Earthquake

• Richter Scale, is a scientific measure of how much energy was released into the Earth

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Measuring an Earthquake

• Modified Mercalli Scale, is an observational measure of how people experience an earthquake

• Mercalli Scale Online

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VOLCANOES!

Two Types of Eruptions

• Violent/Explosive• Quiet/Flowing

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Trapped Gas

• Water vapor and carbon dioxide are trapped in magma.

• At low pressure, they escape quietly when they reach the surface

• At high pressure, they escape violently when they reach the surface

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Magma Composition

• Basaltic – less silica and very fluid, produces quiet eruptions• Granitic – lots of silica, high water

vapor content, and very thick, produces very violent eruptions

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Forms of Volcanoes

• Shield• Cinder Cone• Composite

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Shield Volcanoes

• Formed by quiet eruptions • Basaltic lava builds up in flat layers• Gently sloping slides • For example, Hawaii!

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Cinder Cone Volcano

• Formed by explosive eruptions• Granitic lava thrown high into the air • Lava cools into different sizes of

tephra or ash• Steep-sided,

loose slopes

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Composite Volcano

• A mix of the two types • Quiet or violent• Basaltic or granitic• Steep or gentle slopes• Layered with tephra or ash

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Parts of a Volcano60

Dike

• Magma squeezed into VERTICAL cracks

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Sill

• Magma squeezed into HORIZONTAL cracks

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Ring of Fire

• Region around the Pacific Ocean with frequent earthquakes and volcanoes

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Hot Spot

• Isolated volcano not caused by plate tectonics

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Caldera

• Large crater caused by a violent volcanic eruption

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