Earthquakes & Volcanoes. BIG Ideas: 1. Most geologic activity occurs at the boundaries between plates. 2. Earthquakes are natural vibrations of the ground,

Earthquakes & Earthquakes & VolcanoesVolcanoes

BIGBIG Ideas: Ideas:

1.1. Most geologic activity occurs at Most geologic activity occurs at the boundaries between plates.the boundaries between plates.

2.2. EarthquakesEarthquakes are natural are natural vibrations of the ground, some of vibrations of the ground, some of which are caused by movement which are caused by movement along fractures in Earth’s crust.along fractures in Earth’s crust.

3.3. VolcanoesVolcanoes develop from magma develop from magma moving upward from deep within moving upward from deep within Earth.Earth.

I. Forces Within EarthI. Forces Within Earth FaultsFaults form when the forces form when the forces

acting on rock acting on rock exceed the rock’s exceed the rock’s strength.strength.

Fault:Fault: a break or a break or crack in Earth’s crack in Earth’s crust along which crust along which movement has movement has occurred.occurred.

Most active Most active faults faults are are located at or located at or near plate near plate boundaries.boundaries.

Earthquakes Earthquakes result when result when movement movement occurs along a occurs along a fault.fault.

Locations of EarthquakesLocations of Earthquakesfrom 1980 to 1990from 1980 to 1990

A. Stress and StrainA. Stress and Strain

StressStress:: the total force acting the total force acting on crustal rocks per unit area.on crustal rocks per unit area.

StrainStrain:: the the deformationdeformation of of materials in response to stress.materials in response to stress.

Rocks that are strained past a Rocks that are strained past a certain point will fracture and certain point will fracture and springspring back to original shape. back to original shape.

•a change in the shape or size of a change in the shape or size of an object due to an applied forcean object due to an applied force•misshapenmisshapen•contort, twist and press out of contort, twist and press out of shape shape

Deformation:Deformation:

Elastic Rebound TheoryElastic Rebound Theory

Three Types of StressThree Types of Stress

1.1. compressioncompression:: decreases decreases volume of materialvolume of material

2.2. tensiontension:: pulls material pulls material apartapart

3.3. shearshear:: causes material to causes material to twisttwist

B. Types of FaultsB. Types of Faults

Facts:•1000 km (621 miles) long•15-20 km (9-12 miles) deep

Parts of an EarthquakeParts of an Earthquake

Focus: spot within the Earth’s crust (lithosphere) where the origin of the Earthquake is located (where slippage along a fault occurs).

Epicenter: spot on the surface of the Earth directly above the focus.

C. Earthquake WavesC. Earthquake Waves

Seismic Waves:Seismic Waves: vibrations of vibrations of the ground produced during the ground produced during an earthquake.an earthquake.

Every earthquake generates Every earthquake generates three (3)three (3) types of seismic types of seismic waves…waves…

Types of Seismic Waves:Types of Seismic Waves:

1. PRIMARY Waves: 1. PRIMARY Waves: P-WAVES P-WAVES travel the fastesttravel the fastest FIRST to be recorded FIRST to be recorded travel through solid travel through solid

AND liquid AND liquid compressional waves compressional waves

that push and pull that push and pull

Think Slinky!Think Slinky!

2. SECONDARY 2. SECONDARY Waves:Waves:

S-WAVES S-WAVES secondsecond to be to be

recordedrecorded only travel only travel

through solid through solid material (NOT material (NOT through liquid)through liquid)

shear waves shear waves that move side that move side to side (like a to side (like a rope)rope)

Which layer of Earth will Which layer of Earth will S-Waves S-Waves NOTNOT travel travel

through?through?

3. SURFACE (LAND) Waves:3. SURFACE (LAND) Waves: travel only along Earth’s travel only along Earth’s

surfacesurface slowest wave (last to be slowest wave (last to be

recorded)recorded) cause the surface of Earth to cause the surface of Earth to

move sideways move sideways andand up and up and down (like ocean waves)down (like ocean waves)

Which waves are the Which waves are the most destructive?most destructive?

Surface WavesSurface Waves (also (also known as L-WAVES) known as L-WAVES) cause the greatest cause the greatest damage.damage.

II. Seismic Waves and II. Seismic Waves and Earth’s InteriorEarth’s Interior

A. A. SeismographSeismograph:: instrument instrument that detects that detects and records and records seismic seismic waveswaves

Seismogram: record Seismogram: record produced by seismographproduced by seismograph

Analyzing a Seismogram:Analyzing a Seismogram:

B. Clues to Earth’s B. Clues to Earth’s InteriorInterior

III. Measuring and III. Measuring and Locating EarthquakesLocating Earthquakes

Scientists measure the Scientists measure the strength and chart the strength and chart the location of location of earthquakes earthquakes using seismic using seismic waveswaves

A. Earthquake A. Earthquake MeasurementMeasurement

magnitude:magnitude: measure of measure of energy released by an energy released by an earthquakeearthquake

Richter ScaleRichter Scale

measures measures energy of the energy of the largest seismic largest seismic waves waves (magnitude) (magnitude) produced produced during an during an earthquakeearthquake

Los Angeles

New York City

Which city would better withstand a catastrophic earthquake?

WHY?

B. Locating EarthquakesB. Locating Earthquakes

scientists graph the arrival scientists graph the arrival times of the P and S wavestimes of the P and S waves

the longer the S wave takes the longer the S wave takes to arrive, the to arrive, the furtherfurther away away the quakethe quake

THREE (3) THREE (3) seismic graph seismic graph stations are required to stations are required to locate the epicenterlocate the epicenter

Finding the epicenter…Finding the epicenter…

DamageDamage Ground Rupture: Damage due to Ground Rupture: Damage due to

ground motion will depend on ground motion will depend on Amplitude, Amplitude, Duration of vibrations, Duration of vibrations, Nature of material building is built on,Nature of material building is built on, Design of structureDesign of structure

Fire Fire Landslides Landslides Tsunamis Tsunamis

tidal (harbor) wave - vertical tidal (harbor) wave - vertical displacement at seafloor due to displacement at seafloor due to earthquake causes giant "ripple" in earthquake causes giant "ripple" in ocean ocean

Nimitz Freeway - Nimitz Freeway - Oakland, 1989Oakland, 1989

Loma Prieta - Ground Loma Prieta - Ground RuptureRupture

Mexico City, 1985Mexico City, 1985

Before

After

Tsunamis:Tsunamis: Giant ocean wave or a Giant ocean wave or a series of waves usually series of waves usually associated with an undersea associated with an undersea earthquake or landslideearthquake or landslide

Formation of a tsunamiFormation of a tsunami

IV. VolcanoesIV. Volcanoes Opening where magma erupts Opening where magma erupts

onto Earth’s surface.onto Earth’s surface.

MAGMA: MAGMA: moltenmolten (liquid) (liquid) rock rock UNDERGROUNDUNDERGROUND

LAVA: LAVA: moltenmolten rock that is rock that is ON ON THE SURFACETHE SURFACE

VENT: opening VENT: opening through which through which lava flowslava flows

VOLCANO: the VOLCANO: the build up of build up of material material around the around the ventvent

A. MAJOR VOLCANIC A. MAJOR VOLCANIC ZONESZONES

Most volcanic activity is Most volcanic activity is associated with:associated with:

subduction,subduction, rifting, or rifting, or seafloor spreadingseafloor spreading

1. Pacific Ring of Fire1. Pacific Ring of Fire

2.2. Mid-Ocean Ridges:Mid-Ocean Ridges:rifting and rifting and seafloor spreadingseafloor spreading

3. Hot Spots: Volcanism 3. Hot Spots: Volcanism within plateswithin plates

Hot Spot volcanic activity is Hot Spot volcanic activity is exceptional because…exceptional because…

this activity is this activity is NOTNOT related to related to plate boundaries!plate boundaries!

B. TYPES OF VOLCANOES B. TYPES OF VOLCANOES

1. 1. SHIELD: SHIELD: LAYERS OF LAVA LAYERS OF LAVA WIDE AND FLAT WIDE AND FLAT

Hawaiian Islands

2. 2. CINDER CONE: CINDER CONE: STEEP STEEP LAYERS OF PYROCLASTIC LAYERS OF PYROCLASTIC

MATERIALMATERIAL

small, most common type of volcano

3. COMPOSITE: 3. COMPOSITE: STEEP WITH STEEP WITH LAYERS OF ALTERNATING LAYERS OF ALTERNATING LAVA AND PYROCLASTIC LAVA AND PYROCLASTIC

MATERIALMATERIAL

Mount Saint Helens

SKYLIGHT – WINDOW INTO THE SKYLIGHT – WINDOW INTO THE EARTH’S INTERIOR EARTH’S INTERIOR