M R S . B A K E RC J C B 2 0 1 5

EARTHQUAKES

CAUSES OF EARTHQUAKES

• Earthquake – a shaking of Earth’s crust caused by a release of energy.

• Occur for many reasons:• Eruption of a volcano• Collapse of a cavern• Impact of a meteor• Strain that builds up along faults at or near boundaries

between lithospheric plates. cause of most earthquakes

CAUSES OF EARTHQUAKES

• Elastic-rebound theory• Friction prevents the plates from moving, so strain builds

up, causing the plates to deform.• The strain will become great enough to overcome the

friction and the plates move, causing an earthquake.• The plates then snap back to the shape that they had

before the earthquake, but are in different locations.

CAUSES OF EARTHQUAKES

• Fault – break in the lithosphere along which plate movement has occurred.• Hanging wall—rock on top of fault plane• Footwall—rock below fault plane

• Focus – the point at which the first movement occurs during an earthquake.

• Epicenter – the point on Earth’s surface directly above the focus.

FOUR TYPES OF FAULTS

• Normal

• Reverse

• Thrust (low-angle reverse)

• Strike-slip

FOUR TYPES OF FAULTS

• Normal• Hanging wall moves down relative to footwall• Usually forms from stress at divergent boundary

FOUR TYPES OF FAULTS

• Reverse• Hanging wall moves up relative to footwall• Usually forms from compression at convergent boundary

• Thrust• A low angle (<45 degrees) reverse fault

FOUR TYPES OF FAULTS

• Strike-slip• Movement is horizontal

• Usually forms at a transform boundary

FAULTING, FOLDING, AND MOUNTAINBUILDING

• When large blocks of crust are moved, they may be tilted up to form mountains• Blocks of crust can be pushed straight up to form

mountains• One block may drop relative to another, creating

mountains and valleys• Large scale compression and folding can result in

folded mountains and folded mountain ranges, particularly when two continental plates meet at a convergent boundary.

THREE TYPES OF SEISMIC WAVES

• P waves• S waves• Surface waves

BODY WAVES

• Body waves – waves that travel from the focus of an earthquake through Earth.

• P waves• Primary waves• Compression or longitudinal waves (parallel to motion)• Squeeze and stretch rock materials as they pass through

Earth.• Can travel through any material – solid rock, magma,

ocean water, and air.• Fastest of the wave types; first to be felt and recorded

BODY WAVES

• S waves• shear waves or secondary waves• Cause particles of rock material to move at right

angles to the direction in which the waves are traveling—transverse waves

• Can travel through solid material, but not liquids or gases.

SURFACE WAVES

• Surface waves – earthquake waves that travel along Earth’s surface.

• Travel both up-and-down and side-to-side• Like ripples in a pond

• P and S waves produce surface waves

• Do much damage on Earth’s surface

• Seismograph – an instrument that detects and records waves produced by earthquakes.• Also called a seismometer

• Different types of seismographs record different types of wave motion.

SEISMOGRAPHS

• A common type has a heavy weight attached to a base anchored in bedrock.• The weight stays almost perfectly still even when there is

an earthquake.

• Seismogram – a record sheet that records earthquake movement.

SEISMOGRAPHS

• P waves travel faster than S waves and therefore arrive at a seismograph station first.

• P and S waves produce different patterns on a seismogram.

• As the waves travel farther from the epicenter, the S waves will fall behind the P waves more and more.

• Can be used to know what cities are closer or farther away from the epicenter.

INTERPRETING A SEISMOGRAM

• A seismogram tells the distance between the epicenter and the recording station, but does not give enough information to locate the epicenter.• The distance is calculated using the difference between

the time the p wave is detected and the s wave is detected.

• Information from additional recording stations is required.• Three different seismograph stations are needed to

pinpoint the epicenter “TRIANGULATION”

LOCATING THE EPICENTER

• Knowing the distance a city is from the epicenter, a circle can be drawn with a radius equal to that distance.

• Draw circles for at least three cities and where they intersect is the location of the epicenter.

LOCATING THE EPICENTER

• The magnitude of an earthquake indicates how strong it is.

• The most commonly used scale is the Richter Scale.

• Each increasing number on the Richter Scale indicates 32 times the energy of the number before.

MEASURING AN EARTHQUAKE’S MAGNITUDE

• How much more powerful is a 4 magnitude earthquake than a 3 magnitude?• 32 times

• How much more powerful is an 8 magnitude earthquake than a 5 magnitude?• 32 x 32 x 32 = the difference in energy

MEASURING AN EARTHQUAKE’S MAGNITUDE

MEASURING EARTHQUAKE ACTIVITY

• Mercalli Scale- measures relative intensity of earthquakes by observing the effects on Earth’s surface• Scale goes from I (barely felt, if at all) to XII

(total destruction)• Intensity is not a measure of energy (like

magnitude) but of effect on Earth’s surface

EARTHQUAKE ACTIVITYAND PLATE TECTONICS

Plate Boundaries Earthquake Activity

Earthquakes are concentrated at plate tectonic boundaries• Deepest earthquakes along subduction zones

EARTHQUAKE ACTIVITYAND PLATE TECTONICS

• The most earthquakes occur along the Ring of Fire, the area around the edge of the Pacific Plate• The Pacific Plate is the most active tectonic plate

EARTHQUAKES IN THE UNITED STATES

• Every state within the United States has had some type of seismic movement.

AREAS OF EARTHQUAKE ACTIVITY

• STRONG ACTIVITY:

California, Oregon, and Washington

• Due to subduction of the Juan de Fuca Plate with the North American Plate

AREAS OF EARTHQUAKE ACTIVITY

• Alaska• due to subduction of

the Pacific Plate

• New Madrid Seismic Zone (MO) • weakness and old faults due to

ancient (failed) rift zone • earthquakes in response to

movement of North American Plate

HAWAII• due to volcanic

activity

HOT SPOT MOVEMENT!

ARE THERE EARTHQUAKES IN VA?

• Yes! • But Virginia is a stable area, NOT on the edge of a tectonic plate

• So earthquakes are irregular and very rarely over a 4.5 on the Richter Scale

• However, stable ground means we feel it far away from epicenter

AND VOLCANOES

HAZARDS ASSOCIATED WITH EARTHQUAKES

VOLCANIC HAZARDS

• Lava Flows• Ash Falls• Volcanic Bombs• Pyroclastic Flows• Lahars• Toxic Gases• Earthquakes• Tsunamis• More…

TEPHRA

- The material that is blown out of a volcano and into the air during a violent eruption.- This is also known as pyroclastic material. There a 5 general categories of tephra that are primarily separated according to size:

Volcanic Dust

Volcanic Ash

Lapilli

Volcanic Blocks

Volcanic Bombs

PYROCLASTIC FLOWS

Pyroclastic flows are high density mixtures of hot, dry rock fragments and hot gases that move away from the vent that erupted them at high speeds(hundreds of miles per hour).

LAHARS

A volcanic mudflow. - lethal mixtures of water and

tephra with consistency of wet concrete

- flow down the slopes of volcanoes or down river valleys at rapid speeds, similar to fast-moving streams of water

- buries all in the way

- can carry huge boulders

TOXIC GASES

Sulfur dioxide (SO2- colorless gas with a pungent odor that irritates skin and the

tissues and mucous membranes of the eyes, nose, and throat

- creates haze that affects global temperatures

- contributes to acid rain

TOXIC GASES

CO2 (carbon dioxide):- may become concentrated

at levels lethal to people and animals.

- heavier than air.

Hydrogen Fluoride (HF)- powerful caustic irritant

- can cause conjunctivitis, skin irritation, bone degeneration and mottling of teeth.

- significant cause of death and injury in livestock during ash eruptions and even afterwards, if eat HF-tainted grass

1986: Lake Nyos, Cameroon - Massive death within 15 miles - CO2 gases due to extinct volcano

EARTHQUAKE HAZARDS

• Collapsing buildings claim the majority of lives, but the destruction is often compounded by

• Tsunamis

• Mud Slides

• Fires

• Floods

EARTHQUAKE DAMAGEHaiti Earthquake-

7.0 Magnitude

January 12, 2010

-230,000 people died

-300,000 people injured

-1,000,000 people homeless

EARTHQUAKE DAMAGE

Loma Prieta Earthquake- “World Series Earthquake”

6.9 Magnitude

October 17, 1989

- Heaviest damage in San Francisco Bay area, 60 miles north of epicenter

-63 deaths, 3,757 injuries

- estimated $6 billion in property damage

LOMA PRIETA EARTHQUAKE DAMAGE

at Stanford University

Room where Mrs. Brause was when it hit

EARTHQUAKE SIDE EFFECTS

• Tsunami – a giant sea wave typically produced by an underwater earthquake.

• Also can be caused by underwater landslides and volcanoes

• Known as a tidal wave.• A tsunami can travel long

distances at speeds up to 500 mph

• In 1946, an 7.8 magnitude earthquake near Alaska caused a 46-foot Tsunami that reached Hawaii

• 80% of tsunamis in Ring of Fire

BOXING DAY TSUNAMIDECEMBER 26, 2004

- Earthquake with epicenter off west coast of Sumatra, - magnitude 9.1–9.3 -- the third largest earthquake ever

recorded on a seismograph.

- longest duration of faulting ever observed, between 8.3 and 10 minutes.

- located in a subduction zone

- Tsunami:- Earthquake triggered a series of devastating tsunamis along the

coasts of most landmasses bordering the Indian Ocean; Indonesia was the hardest-hit country, followed by Sri Lanka, India, Thailand.

- coastal communities inundated with waves up to 98 ft high.

- over 230,000 people killed in fourteen countries; ne of the deadliest natural disasters in recorded history.

JAPAN EARTHQUAKE & TSUNAMI

Japan Earthquake 2011:8.9 Magnitude Earthquake Hits, 30-Foot Tsunami Triggered The earthquake:

- shifted Earth on its axis of rotation

- -shortened the length of a day by about a microsecond

- moved Japan's main island of Honshu eastward by 2.4 m

- most deaths due to Tsunami

• Scientists study buildings after earthquakes to see which types of structures sustain the most and least amount of damage.

• Building codes in earthquake zones are designed to prevent structural collapse.

• Leads to better designs for bridges, buildings, etc.

PREVENTING EARTHQUAKE DAMAGE

• In the United States, many places are obvious because they lie along plate boundaries.• Alaska• California• Western states

• New Madrid Fault – Missouri, not so obvious, not along plate boundaries – but some of the largest earthquakes in U.S. history.

EARTHQUAKE RISK

• Must be able to predict three things:• Where the earthquake will occur.• When the earthquake will occur.• The magnitude of the earthquake that will occur.

• Can make long-term predictions based on past earthquake activity.

• Scientists can also identify seismic gaps which are areas where faults have not moved over a period. May indicate that tension is building and an earthquake might be developing.

PREDICTING EARTHQUAKES